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* rcu: Fix accelerated grace periods for last non-dynticked CPUPaul E. McKenney2010-02-27
| | | | | | | | | | | | | | | | | | | | | | It is invalid to invoke __rcu_process_callbacks() with irqs disabled, so do it indirectly via raise_softirq(). This requires a state-machine implementation to cycle through the grace-period machinery the required number of times. Located-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <1267231138-27856-1-git-send-email-paulmck@linux.vnet.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Make rcu_read_lock_sched_held() take boot time into accountPaul E. McKenney2010-02-26
| | | | | | | | | | | | | | | | | | | | Before the scheduler starts, all tasks are non-preemptible by definition. So, during that time, rcu_read_lock_sched_held() needs to always return "true". This patch makes that be so. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <1267135607-7056-2-git-send-email-paulmck@linux.vnet.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Add RCU_CPU_STALL_VERBOSE to dump detailed per-task informationPaul E. McKenney2010-02-25
| | | | | | | | | | | | | | | | | | | | | | When RCU detects a grace-period stall, it currently just prints out the PID of any tasks doing the stalling. This patch adds RCU_CPU_STALL_VERBOSE, which enables the more-verbose reporting from sched_show_task(). Suggested-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <1266887105-1528-21-git-send-email-paulmck@linux.vnet.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Fix deadlock in TREE_PREEMPT_RCU CPU stall detectionPaul E. McKenney2010-02-25
| | | | | | | | | | | | | | | | | | | | | | | | | | Under TREE_PREEMPT_RCU, print_other_cpu_stall() invokes rcu_print_task_stall() with the root rcu_node structure's ->lock held, and rcu_print_task_stall() acquires that same lock for self-deadlock. Fix this by removing the lock acquisition from rcu_print_task_stall(), and making all callers acquire the lock instead. Tested-by: John Kacur <jkacur@redhat.com> Tested-by: Thomas Gleixner <tglx@linutronix.de> Located-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <1266887105-1528-19-git-send-email-paulmck@linux.vnet.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Convert to raw_spinlocksPaul E. McKenney2010-02-25
| | | | | | | | | | | | | | | | | | | | The spinlocks in rcutree need to be real spinlocks in preempt-rt. Convert them to raw_spinlocks. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <1266887105-1528-18-git-send-email-paulmck@linux.vnet.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Stop overflowing signed integersPaul E. McKenney2010-02-25
| | | | | | | | | | | | | | | | | | | | | | | | | The C standard does not specify the result of an operation that overflows a signed integer, so such operations need to be avoided. This patch changes the type of several fields from "long" to "unsigned long" and adjusts operations as needed. ULONG_CMP_GE() and ULONG_CMP_LT() macros are introduced to do the modular comparisons that are appropriate given that overflow is an expected event. Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <1266887105-1528-17-git-send-email-paulmck@linux.vnet.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Accelerate grace period if last non-dynticked CPUPaul E. McKenney2010-02-25
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Currently, rcu_needs_cpu() simply checks whether the current CPU has an outstanding RCU callback, which means that the last CPU to go into dyntick-idle mode might wait a few ticks for the relevant grace periods to complete. However, if all the other CPUs are in dyntick-idle mode, and if this CPU is in a quiescent state (which it is for RCU-bh and RCU-sched any time that we are considering going into dyntick-idle mode), then the grace period is instantly complete. This patch therefore repeatedly invokes the RCU grace-period machinery in order to force any needed grace periods to complete quickly. It does so a limited number of times in order to prevent starvation by an RCU callback function that might pass itself to call_rcu(). However, if any CPU other than the current one is not in dyntick-idle mode, fall back to simply checking (with fix to bug noted by Lai Jiangshan). Also, take advantage of last grace-period forcing, the opportunity to do so noted by Steve Rostedt. And apply simplified #ifdef condition suggested by Frederic Weisbecker. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <1266887105-1528-15-git-send-email-paulmck@linux.vnet.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Fix sparse warningsPaul E. McKenney2010-01-16
| | | | | | | | | | | | | | | | | | | | Rename local variable "i" in rcu_init() to avoid conflict with RCU_INIT_FLAVOR(), restrict the scope of RCU_TREE_NONCORE, and make __synchronize_srcu() static. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12635142581560-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Give different levels of the rcu_node hierarchy distinct lockdep namesPaul E. McKenney2010-01-13
| | | | | | | | | | | | | | | | | | | | | | | | | Previously, each level of the rcu_node hierarchy had the same rather unimaginative name: "&rcu_node_class[i]". This makes lockdep diagnostics involving these lockdep classes less helpful than would be nice. This patch fixes this by giving each level of the rcu_node hierarchy a distinct name: "rcu_node_level_0", "rcu_node_level_1", and so on. This version of the patch includes improved diagnostics suggested by Josh Triplett and Peter Zijlstra. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12626498421830-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Add force_quiescent_state() testing to rcutorturePaul E. McKenney2010-01-13
| | | | | | | | | | | | | | | | | | | | | | Add force_quiescent_state() testing to rcutorture, with a separate thread that repeatedly invokes force_quiescent_state() in bursts. This can greatly increase the probability of encountering certain types of race conditions. Suggested-by: Josh Triplett <josh@joshtriplett.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <1262646551116-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Make force_quiescent_state() start grace period if neededPaul E. McKenney2010-01-13
| | | | | | | | | | | | | | | | | | | | | | | | Grace periods cannot be started while force_quiescent_state() is active. This is OK in that the affected CPUs will try again later, but it does induce needless grace-period delays. This patch causes rcu_start_gp() to record a failed attempt to start a grace period. When force_quiescent_state() prepares to return, it then starts the grace period if there was such a failed attempt. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12626465501854-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Remove redundant grace-period checkPaul E. McKenney2010-01-13
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The rcu_process_dyntick() function checks twice for the end of the current grace period. However, it holds the current rcu_node structure's ->lock field throughout, and doesn't get to the second call to rcu_gp_in_progress() unless there is at least one CPU corresponding to this rcu_node structure that has not yet checked in for the current grace period, which would prevent the current grace period from ending. So the current grace period cannot have ended, and the second check is redundant, so remove it. Also, given that this function is used even with !CONFIG_NO_HZ, its name is quite misleading. Change from rcu_process_dyntick() to force_qs_rnp(). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <1262646550562-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Remove leg of force_quiescent_state() switch statementPaul E. McKenney2010-01-13
| | | | | | | | | | | | | | | | | | | | | | | | | | The comparisons of rsp->gpnum nad rsp->completed in rcu_process_dyntick() and force_quiescent_state() can be replaced by the much more clear rcu_gp_in_progress() predicate function. After doing this, it becomes clear that the RCU_SAVE_COMPLETED leg of the force_quiescent_state() function's switch statement is almost completely a no-op. A small change to the RCU_SAVE_DYNTICK leg renders it a complete no-op, after which it can be removed. Doing so also eliminates the forcenow local variable from force_quiescent_state(). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12626465501781-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Eliminate rcu_process_dyntick() return valuePaul E. McKenney2010-01-13
| | | | | | | | | | | | | | | | | | | | | | | | | | | Because a new grace period cannot start while we are executing within the force_quiescent_state() function's switch statement, if any test within that switch statement or within any function called from that switch statement shows that the current grace period has ended, we can safely re-do that test any time before we leave the switch statement. This means that we no longer need a return value from rcu_process_dyntick(), as we can simply invoke rcu_gp_in_progress() to check whether the old grace period has finished -- there is no longer any need to worry about whether or not a new grace period has been started. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12626465501857-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Eliminate second argument of rcu_process_dyntick()Paul E. McKenney2010-01-13
| | | | | | | | | | | | | | | | | | | | | | | At this point, the second argument to all calls to rcu_process_dyntick() is a function of the same field of the structure passed in as the first argument, namely, rsp->gpnum-1. So propagate rsp->gpnum-1 to all uses of the second argument within rcu_process_dyntick() and then eliminate the second argument. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12626465503786-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Eliminate local variable lastcomp from force_quiescent_state()Paul E. McKenney2010-01-13
| | | | | | | | | | | | | | | | | | | | | | Because rsp->fqs_active is set to 1 across force_quiescent_state()'s switch statement, rcu_start_gp() will refrain from starting a new grace period during this time. Therefore, rsp->gpnum is constant, and can be propagated to all uses of lastcomp, eliminating this local variable. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12626465502985-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Eliminate local variable signaled from force_quiescent_state()Paul E. McKenney2010-01-13
| | | | | | | | | | | | | | | | | | | | | Because the root rcu_node lock is held across entry to the switch statement in force_quiescent_state(), it is no longer necessary to snapshot rsp->signaled to a local variable. Eliminate both the snapshotting and the local variable. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <1262646550602-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Prohibit starting new grace periods while forcing quiescent statesPaul E. McKenney2010-01-13
| | | | | | | | | | | | | | | | | | | | | | | | | Reduce the number and variety of race conditions by prohibiting the start of a new grace period while force_quiescent_state() is active. A new fqs_active flag in the rcu_state structure is used to trace whether or not force_quiescent_state() is active, and this new flag is tested by rcu_start_gp(). If the CPU that closed out the last grace period needs another grace period, this new grace period may be delayed up to one scheduling-clock tick, but it will eventually get started. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <126264655052-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Adjust force_quiescent_state() locking, step 2Paul E. McKenney2010-01-13
| | | | | | | | | | | | | | | | | | | | | | | This patch releases rnp->lock after the end of force_quiescent_state()'s switch statement. This is a second step towards prohibiting starting grace periods while force_quiescent_state() is executing, which will reduce the number and complexity of races that force_quiescent_state() is involved in. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12626465501994-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Adjust force_quiescent_state() locking, step 1Paul E. McKenney2010-01-13
| | | | | | | | | | | | | | | | | | | | | | | This causes rnp->lock to be held on entry to force_quiescent_state()'s switch statement. This is a first step towards prohibiting starting grace periods while force_quiescent_state() is executing, which will reduce the number and complexity of races that force_quiescent_state() is involved in. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12626465501455-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Add expedited grace-period support for preemptible RCUPaul E. McKenney2009-12-03
| | | | | | | | | | | | | | | | | | | | | | | Implement an synchronize_rcu_expedited() for preemptible RCU that actually is expedited. This uses synchronize_sched_expedited() to force all threads currently running in a preemptible-RCU read-side critical section onto the appropriate ->blocked_tasks[] list, then takes a snapshot of all of these lists and waits for them to drain. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <1259784616158-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Enable fourth level of TREE_RCU hierarchyPaul E. McKenney2009-12-03
| | | | | | | | | | | | | | | | | | | | | | | | | | Enable a fourth level of rcu_node hierarchy for TREE_RCU and TREE_PREEMPT_RCU. This is for stress-testing and experiemental purposes only, although in theory this would enable 16,777,216 CPUs on 64-bit systems, though only 1,048,576 CPUs on 32-bit systems. Normal experimental use of this fourth level will normally set CONFIG_RCU_FANOUT=2, requiring a 16-CPU system, though the more adventurous (and more fortunate) experimenters may wish to chose CONFIG_RCU_FANOUT=3 for 81-CPU systems or even CONFIG_RCU_FANOUT=4 for 256-CPU systems. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Josh Triplett <josh@joshtriplett.org> Acked-by: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12597846161257-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Rename "quiet" functionsPaul E. McKenney2009-12-03
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The number of "quiet" functions has grown recently, and the names are no longer very descriptive. The point of all of these functions is to do some portion of the task of reporting a quiescent state, so rename them accordingly: o cpu_quiet() becomes rcu_report_qs_rdp(), which reports a quiescent state to the per-CPU rcu_data structure. If this turns out to be a new quiescent state for this grace period, then rcu_report_qs_rnp() will be invoked to propagate the quiescent state up the rcu_node hierarchy. o cpu_quiet_msk() becomes rcu_report_qs_rnp(), which reports a quiescent state for a given CPU (or possibly a set of CPUs) up the rcu_node hierarchy. o cpu_quiet_msk_finish() becomes rcu_report_qs_rsp(), which reports a full set of quiescent states to the global rcu_state structure. o task_quiet() becomes rcu_report_unblock_qs_rnp(), which reports a quiescent state due to a task exiting an RCU read-side critical section that had previously blocked in that same critical section. As indicated by the new name, this type of quiescent state is reported up the rcu_node hierarchy (using rcu_report_qs_rnp() to do so). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Josh Triplett <josh@joshtriplett.org> Acked-by: Lai Jiangshan <laijs@cn.fujitsu.com> Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12597846163698-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Re-arrange code to reduce #ifdef painPaul E. McKenney2009-11-22
| | | | | | | | | | | | | | | | | | | | | | | Remove #ifdefs from kernel/rcupdate.c and include/linux/rcupdate.h by moving code to include/linux/rcutiny.h, include/linux/rcutree.h, and kernel/rcutree.c. Also remove some definitions that are no longer used. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <1258908830885-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Eliminate unneeded function wrappingPaul E. McKenney2009-11-22
| | | | | | | | | | | | | | | | | | | | | | | | | The functions rcu_init() is a wrapper for __rcu_init(), and also sets up the CPU-hotplug notifier for rcu_barrier_cpu_hotplug(). But TINY_RCU doesn't need CPU-hotplug notification, and the rcu_barrier_cpu_hotplug() is a simple wrapper for rcu_cpu_notify(). So push rcu_init() out to kernel/rcutree.c and kernel/rcutiny.c and get rid of the wrapper function rcu_barrier_cpu_hotplug(). Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12589088302320-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Fix grace-period-stall bug on large systems with CPU hotplugPaul E. McKenney2009-11-22
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | When the last CPU of a given leaf rcu_node structure goes offline, all of the tasks queued on that leaf rcu_node structure (due to having blocked in their current RCU read-side critical sections) are requeued onto the root rcu_node structure. This requeuing is carried out by rcu_preempt_offline_tasks(). However, it is possible that these queued tasks are the only thing preventing the leaf rcu_node structure from reporting a quiescent state up the rcu_node hierarchy. Unfortunately, the old code would fail to do this reporting, resulting in a grace-period stall given the following sequence of events: 1. Kernel built for more than 32 CPUs on 32-bit systems or for more than 64 CPUs on 64-bit systems, so that there is more than one rcu_node structure. (Or CONFIG_RCU_FANOUT is artificially set to a number smaller than CONFIG_NR_CPUS.) 2. The kernel is built with CONFIG_TREE_PREEMPT_RCU. 3. A task running on a CPU associated with a given leaf rcu_node structure blocks while in an RCU read-side critical section -and- that CPU has not yet passed through a quiescent state for the current RCU grace period. This will cause the task to be queued on the leaf rcu_node's blocked_tasks[] array, in particular, on the element of this array corresponding to the current grace period. 4. Each of the remaining CPUs corresponding to this same leaf rcu_node structure pass through a quiescent state. However, the task is still in its RCU read-side critical section, so these quiescent states cannot be reported further up the rcu_node hierarchy. Nevertheless, all bits in the leaf rcu_node structure's ->qsmask field are now zero. 5. Each of the remaining CPUs go offline. (The events in step #4 and #5 can happen in any order as long as each CPU passes through a quiescent state before going offline.) 6. When the last CPU goes offline, __rcu_offline_cpu() will invoke rcu_preempt_offline_tasks(), which will move the task to the root rcu_node structure, but without reporting a quiescent state up the rcu_node hierarchy (and this failure to report a quiescent state is the bug). But because this leaf rcu_node structure's ->qsmask field is already zero and its ->block_tasks[] entries are all empty, force_quiescent_state() will skip this rcu_node structure. Therefore, grace periods are now hung. This patch abstracts some code out of rcu_read_unlock_special(), calling the result task_quiet() by analogy with cpu_quiet(), and invokes task_quiet() from both rcu_read_lock_special() and __rcu_offline_cpu(). Invoking task_quiet() from __rcu_offline_cpu() reports the quiescent state up the rcu_node hierarchy, fixing the bug. This ends up requiring a separate lock_class_key per level of the rcu_node hierarchy, which this patch also provides. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12589088301770-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Eliminate __rcu_pending() false positivesPaul E. McKenney2009-11-14
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Now that there are both ->gpnum and ->completed fields in the rcu_node structure, __rcu_pending() should check rdp->gpnum and rdp->completed against rnp->gpnum and rdp->completed, respectively, instead of the prior comparison against the rcu_state fields rsp->gpnum and rsp->completed. Given the old comparison, __rcu_pending() could return 1, resulting in a needless raise_softirq(RCU_SOFTIRQ). This useless work would happen if RCU responded to a scheduling-clock interrupt after the rcu_state fields had been updated, but before the rcu_node fields had been updated. Changing the comparison from the rcu_state fields to the rcu_node fields prevents this useless work from happening. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12581706991966-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Further cleanups of use of lastcompPaul E. McKenney2009-11-14
| | | | | | | | | | | | | | | | | | | | | | | | Now that a copy of the rsp->completed flag is available in all rcu_node structures, make full use of it. It is still legitimate to access rsp->completed while holding the root rcu_node structure's lock, however. Also, tighten up force_quiescent_state()'s checks for end of current grace period. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <1258170699933-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Simplify association of forced quiescent states with grace periodsPaul E. McKenney2009-11-13
| | | | | | | | | | | | | | | | | | | | | | | | | The force_quiescent_state() function also took a snapshot of the ->completed field, which was as obnoxious as it was in rcu_sched_qs() and friends. So snapshot ->gpnum-1. Also, since the dyntick_record_completed() and dyntick_recall_completed() functions are now simple assignments that are independent of CONFIG_NO_HZ, and since their names are now misleading, get rid of them. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12580941042308-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Accelerate callback processing on CPUs not detecting GP endPaul E. McKenney2009-11-13
| | | | | | | | | | | | | | | | | | | | | | | | | | | | An earlier fix for a race resulted in a situation where the CPUs other than the CPU that detected the end of the grace period would not process their callbacks until the next grace period started. This means that these other CPUs would unnecessarily demand that an extra grace period be started. This patch eliminates this extra grace period and speeds callback processing by propagating rsp->completed to the rcu_node structures in the case where the CPU detecting the end of the grace period sees no reason to start a new grace period. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <1258094104417-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Simplify association of quiescent states with grace periodsPaul E. McKenney2009-11-10
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The rdp->passed_quiesc_completed fields are used to properly associate the recorded quiescent state with a grace period. It is OK to wrongly associate a given quiescent state with a preceding grace period, but it is fatal to associate a given quiescent state with a grace period that begins after the quiescent state occurred. Grace periods are numbered, and the following fields track them: o ->gpnum is the number of the grace period currently in progress, or the number of the last grace period to complete if no grace period is currently in progress. o ->completed is the number of the last grace period to have completed. These two fields are equal if there is no grace period in progress, otherwise ->gpnum is one greater than ->completed. But the rdp->passed_quiesc_completed field compared against ->completed, and if equal, the quiescent state is presumed to count against the current grace period. The earlier code copied rdp->completed to rdp->passed_quiesc_completed, which has been made to work, but is error-prone. In contrast, copying one less than rdp->gpnum is guaranteed safe, because rdp->gpnum is not incremented until after the start of the corresponding grace period. At the end of the grace period, when ->completed has incremented, then any quiescent periods recorded previously will be discarded. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12578890421011-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Rename dynticks_completed to completed_fqsPaul E. McKenney2009-11-10
| | | | | | | | | | | | | | | | | | | | | | | This field is used whether or not CONFIG_NO_HZ is set, so the old name of ->dynticks_completed is quite misleading. Change to ->completed_fqs, given that it the value that force_quiescent_state() is trying to drive the ->completed field away from. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12578890423298-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Fix note_new_gpnum() uses of ->gpnumPaul E. McKenney2009-11-09
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Impose a clear locking design on the note_new_gpnum() function's use of the ->gpnum counter. This is done by updating rdp->gpnum only from the corresponding leaf rcu_node structure's rnp->gpnum field, and even then only under the protection of that same rcu_node structure's ->lock field. Performance and scalability are maintained using a form of double-checked locking, and excessive spinning is avoided by use of the spin_trylock() function. The use of spin_trylock() is safe due to the fact that CPUs who fail to acquire this lock will try again later. The hierarchical nature of the rcu_node data structure limits contention (which could be limited further if need be using the RCU_FANOUT kernel parameter). Without this patch, obscure but quite possible races could result in a quiescent state that occurred during one grace period to be accounted to the following grace period, causing this following grace period to end prematurely. Not good! Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com Cc: <stable@kernel.org> # .32.x LKML-Reference: <12571987492350-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Fix synchronization for rcu_process_gp_end() uses of ->completed counterPaul E. McKenney2009-11-09
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Impose a clear locking design on the rcu_process_gp_end() function's use of the ->completed counter. This is done by creating a ->completed field in the rcu_node structure, which can safely be accessed under the protection of that structure's lock. Performance and scalability are maintained by using a form of double-checked locking, so that rcu_process_gp_end() only acquires the leaf rcu_node structure's ->lock if a grace period has recently ended. This fix reduces rcutorture failure rate by at least two orders of magnitude under heavy stress with force_quiescent_state() being invoked artificially often. Without this fix, unsynchronized access to the ->completed field can cause rcu_process_gp_end() to advance callbacks whose grace period has not yet expired. (Bad idea!) Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com Cc: <stable@kernel.org> # .32.x LKML-Reference: <12571987494069-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Prepare for synchronization fixes: clean up for non-NO_HZ handling of ↵Paul E. McKenney2009-11-09
| | | | | | | | | | | | | | | | | | | | | | | ->completed counter Impose a clear locking design on non-NO_HZ handling of the ->completed counter. This increases the distance between the RCU and the CPU-hotplug mechanisms. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com Cc: <stable@kernel.org> # .32.x LKML-Reference: <12571987491353-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* Merge branch 'core/urgent' into core/rcuIngo Molnar2009-11-09
|\ | | | | | | | | | | Merge reason: Pick up RCU fixlet to base further commits on. Signed-off-by: Ingo Molnar <mingo@elte.hu>
| * rcu: Fix long-grace-period race between forcing and initializationPaul E. McKenney2009-11-02
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Very long RCU read-side critical sections (50 milliseconds or so) can cause a race between force_quiescent_state() and rcu_start_gp() as follows on kernel builds with multi-level rcu_node hierarchies: 1. CPU 0 calls force_quiescent_state(), sees that there is a grace period in progress, and acquires ->fsqlock. 2. CPU 1 detects the end of the grace period, and so cpu_quiet_msk_finish() sets rsp->completed to rsp->gpnum. This operation is carried out under the root rnp->lock, but CPU 0 has not yet acquired that lock. Note that rsp->signaled is still RCU_SAVE_DYNTICK from the last grace period. 3. CPU 1 calls rcu_start_gp(), but no one wants a new grace period, so it drops the root rnp->lock and returns. 4. CPU 0 acquires the root rnp->lock and picks up rsp->completed and rsp->signaled, then drops rnp->lock. It then enters the RCU_SAVE_DYNTICK leg of the switch statement. 5. CPU 2 invokes call_rcu(), and now needs a new grace period. It calls rcu_start_gp(), which acquires the root rnp->lock, sets rsp->signaled to RCU_GP_INIT (too bad that CPU 0 is already in the RCU_SAVE_DYNTICK leg of the switch statement!) and starts initializing the rcu_node hierarchy. If there are multiple levels to the hierarchy, it will drop the root rnp->lock and initialize the lower levels of the hierarchy. 6. CPU 0 notes that rsp->completed has not changed, which permits both CPU 2 and CPU 0 to try updating it concurrently. If CPU 0's update prevails, later calls to force_quiescent_state() can count old quiescent states against the new grace period, which can in turn result in premature ending of grace periods. Not good. This patch adds an RCU_GP_IDLE state for rsp->signaled that is set initially at boot time and any time a grace period ends. This prevents CPU 0 from getting into the workings of force_quiescent_state() in step 4. Additional locking and checks prevent the concurrent update of rsp->signaled in step 6. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <1256742889199-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
| * rcu: Fix TREE_PREEMPT_RCU CPU_HOTPLUG bad-luck hangPaul E. McKenney2009-10-15
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | If the following sequence of events occurs, then TREE_PREEMPT_RCU will hang waiting for a grace period to complete, eventually OOMing the system: o A TREE_PREEMPT_RCU build of the kernel is booted on a system with more than 64 physical CPUs present (32 on a 32-bit system). Alternatively, a TREE_PREEMPT_RCU build of the kernel is booted with RCU_FANOUT set to a sufficiently small value that the physical CPUs populate two or more leaf rcu_node structures. o A task is preempted in an RCU read-side critical section while running on a CPU corresponding to a given leaf rcu_node structure. o All CPUs corresponding to this same leaf rcu_node structure record quiescent states for the current grace period. o All of these same CPUs go offline (hence the need for enough physical CPUs to populate more than one leaf rcu_node structure). This causes the preempted task to be moved to the root rcu_node structure. At this point, there is nothing left to cause the quiescent state to be propagated up the rcu_node tree, so the current grace period never completes. The simplest fix, especially after considering the deadlock possibilities, is to detect this situation when the last CPU is offlined, and to set that CPU's ->qsmask bit in its leaf rcu_node structure. This will cause the next invocation of force_quiescent_state() to end the grace period. Without this fix, this hang can be triggered in an hour or so on some machines with rcutorture and random CPU onlining/offlining. With this fix, these same machines pass a full 10 hours of this sort of abuse. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <20091015162614.GA19131@linux.vnet.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* | rcu: Simplify creating of lockdep class for root rcu_nodePeter Zijlstra2009-10-26
|/ | | | | | | | | | | | | | | | | | | | | Use lockdep_set_class() to simplify the code and to avoid any additional overhead in the !LOCKDEP case. Also move the definition of rcu_root_class into kernel/rcutree.c, as suggested by Lai Jiangshan. Signed-off-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <1256577871443-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Prevent RCU IPI storms in presence of high call_rcu() loadPaul E. McKenney2009-10-15
| | | | | | | | | | | | | | | | | | | | | | | | | As the number of callbacks on a given CPU rises, invoke force_quiescent_state() only every blimit number of callbacks (defaults to 10,000), and even then only if no other CPU has invoked force_quiescent_state() in the meantime. This should fix the performance regression reported by Nick. Reported-by: Nick Piggin <npiggin@suse.de> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com Cc: jens.axboe@oracle.com LKML-Reference: <12555405592133-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Place root rcu_node structure in separate lockdep classPaul E. McKenney2009-10-07
| | | | | | | | | | | | | | | | | | | | | | | | | | | Before this patch, all of the rcu_node structures were in the same lockdep class, so that lockdep would complain when rcu_preempt_offline_tasks() acquired the root rcu_node structure's lock while holding one of the leaf rcu_nodes' locks. This patch changes rcu_init_one() to use a separate spin_lock_init() for the root rcu_node structure's lock than is used for that of all of the rest of the rcu_node structures, which puts the root rcu_node structure's lock in its own lockdep class. Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12548908983277-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Make hot-unplugged CPU relinquish its own RCU callbacksPaul E. McKenney2009-10-07
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | The current interaction between RCU and CPU hotplug requires that RCU block in CPU notifiers waiting for callbacks to drain. This can be greatly simplified by having each CPU relinquish its own callbacks, and for both _rcu_barrier() and CPU_DEAD notifiers to adopt all callbacks that were previously relinquished. This change also eliminates the possibility of certain types of hangs due to the previous practice of waiting for callbacks to be invoked from within CPU notifiers. If you don't every wait, you cannot hang. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <1254890898456-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Move rcu_barrier() to rcutreePaul E. McKenney2009-10-07
| | | | | | | | | | | | | | | | | | | | | | | | Move the existing rcu_barrier() implementation to rcutree.c, consistent with the fact that the rcu_barrier() implementation is tied quite tightly to the RCU implementation. This opens the way to simplify and fix rcutree.c's rcu_barrier() implementation in a later patch. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12548908982563-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Clean up code based on review feedback from Josh Triplett, part 4Paul E. McKenney2009-10-05
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | These issues identified during an old-fashioned face-to-face code review extending over many hours. This group improves an existing abstraction and introduces two new ones. It also fixes an RCU stall-warning bug found while making the other changes. o Make RCU_INIT_FLAVOR() declare its own variables, removing the need to declare them at each call site. o Create an rcu_for_each_leaf() macro that scans the leaf nodes of the rcu_node tree. o Create an rcu_for_each_node_breadth_first() macro that does a breadth-first traversal of the rcu_node tree, AKA stepping through the array in index-number order. o If all CPUs corresponding to a given leaf rcu_node structure go offline, then any tasks queued on that leaf will be moved to the root rcu_node structure. Therefore, the stall-warning code must dump out tasks queued on the root rcu_node structure as well as those queued on the leaf rcu_node structures. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12541491934126-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Clean up code based on review feedback from Josh Triplett, part 3Paul E. McKenney2009-10-05
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Whitespace fixes, updated comments, and trivial code movement. o Fix whitespace error in RCU_HEAD_INIT() o Move "So where is rcu_write_lock()" comment so that it does not come between the rcu_read_unlock() header comment and the rcu_read_unlock() definition. o Move the module_param statements for blimit, qhimark, and qlowmark to immediately follow the corresponding definitions. o In __rcu_offline_cpu(), move the assignment to rdp_me inside the "if" statement, given that rdp_me is not used outside of that "if" statement. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12541491931164-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Fix rcu_lock_map build failure on CONFIG_PROVE_LOCKING=yPaul E. McKenney2009-10-05
| | | | | | | | | Move the rcu_lock_map definition from rcutree.c to rcupdate.c so that TINY_RCU can use lockdep. Reported-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Clean up code to address Ingo's checkpatch feedbackPaul E. McKenney2009-09-23
| | | | | | | | | | | | | | | | | | | Move declarations and update storage classes to make checkpatch happy. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12537246441701-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Clean up code based on review feedback from Josh Triplett, part 2Paul E. McKenney2009-09-23
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | These issues identified during an old-fashioned face-to-face code review extending over many hours. o Add comments for tricky parts of code, and correct comments that have passed their sell-by date. o Get rid of the vestiges of rcu_init_sched(), which is no longer needed now that PREEMPT_RCU is gone. o Move the #include of rcutree_plugin.h to the end of rcutree.c, which means that, rather than having a random collection of forward declarations, the new set of forward declarations document the set of plugins. The new home for this #include also allows __rcu_init_preempt() to move into rcutree_plugin.h. o Fix rcu_preempt_check_callbacks() to be static. Suggested-by: Josh Triplett <josh@joshtriplett.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12537246443924-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu> Peter Zijlstra <peterz@infradead.org>
* rcu: Clean up code based on review feedback from Josh TriplettPaul E. McKenney2009-09-23
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | These issues identified during an old-fashioned face-to-face code review extended over many hours. o Bury various forms of the "rsp->completed == rsp->gpnum" comparison into an rcu_gp_in_progress() function, which has the beneficial side-effect of forcing consistent use of ACCESS_ONCE(). o Replace hand-coded arithmetic with DIV_ROUND_UP(). o Bury several "!list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x01])" instances into an rcu_preempted_readers() function, as this expression indicates that there are no readers blocked within RCU read-side critical sections blocking the current grace period. (Though there might well be similar readers blocking the next grace period.) o Remove a dangling rcu_restart_cpu() declaration that has been dangling for almost 20 minor releases of the kernel. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu Cc: dhowells@redhat.com LKML-Reference: <12537246442687-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
* rcu: Fix whitespace inconsistenciesPaul E. McKenney2009-09-19
| | | | | | | | | | | | | | | | | | | | Fix a number of whitespace ^Ierrors in the include/linux/rcu* and the kernel/rcu* files. Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: laijs@cn.fujitsu.com Cc: dipankar@in.ibm.com Cc: akpm@linux-foundation.org Cc: mathieu.desnoyers@polymtl.ca Cc: josh@joshtriplett.org Cc: dvhltc@us.ibm.com Cc: niv@us.ibm.com Cc: peterz@infradead.org Cc: rostedt@goodmis.org Cc: Valdis.Kletnieks@vt.edu LKML-Reference: <20090918172819.GA24405@linux.vnet.ibm.com> [ did more checkpatch fixlets ] Signed-off-by: Ingo Molnar <mingo@elte.hu>
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