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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2009-09-13 12:15:09 -0400
committerIngo Molnar <mingo@elte.hu>2009-09-17 18:06:13 -0400
commitb0e165c035b13e1074fa0b555318bd9cb7102558 (patch)
treec65de438df4e8ad3e9e562663b377d61cc87af57
parentbbe3eae8bb039b5ffd64a6e3d1a0deaa1f3cbae9 (diff)
rcu: Add debug checks to TREE_PREEMPT_RCU for premature grace periods
Check to make sure that there are no blocked tasks for the previous grace period while initializing for the next grace period, verify that rcu_preempt_qs() is given the correct CPU number and is never called for an offline CPU. 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: <12528585111986-git-send-email-> Signed-off-by: Ingo Molnar <mingo@elte.hu>
-rw-r--r--kernel/rcutree.c2
-rw-r--r--kernel/rcutree_plugin.h25
2 files changed, 27 insertions, 0 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index da301e2fd84f..e9a4ae94647f 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -632,6 +632,7 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
632 /* Special-case the common single-level case. */ 632 /* Special-case the common single-level case. */
633 if (NUM_RCU_NODES == 1) { 633 if (NUM_RCU_NODES == 1) {
634 rnp->qsmask = rnp->qsmaskinit; 634 rnp->qsmask = rnp->qsmaskinit;
635 rcu_preempt_check_blocked_tasks(rnp);
635 rnp->gpnum = rsp->gpnum; 636 rnp->gpnum = rsp->gpnum;
636 rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state OK. */ 637 rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state OK. */
637 spin_unlock_irqrestore(&rnp->lock, flags); 638 spin_unlock_irqrestore(&rnp->lock, flags);
@@ -665,6 +666,7 @@ rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
665 for (rnp_cur = &rsp->node[0]; rnp_cur < rnp_end; rnp_cur++) { 666 for (rnp_cur = &rsp->node[0]; rnp_cur < rnp_end; rnp_cur++) {
666 spin_lock(&rnp_cur->lock); /* irqs already disabled. */ 667 spin_lock(&rnp_cur->lock); /* irqs already disabled. */
667 rnp_cur->qsmask = rnp_cur->qsmaskinit; 668 rnp_cur->qsmask = rnp_cur->qsmaskinit;
669 rcu_preempt_check_blocked_tasks(rnp);
668 rnp->gpnum = rsp->gpnum; 670 rnp->gpnum = rsp->gpnum;
669 spin_unlock(&rnp_cur->lock); /* irqs already disabled. */ 671 spin_unlock(&rnp_cur->lock); /* irqs already disabled. */
670 } 672 }
diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index 47789369ea59..b8e4b0384f00 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -86,6 +86,7 @@ static void rcu_preempt_qs(int cpu)
86 86
87 if (t->rcu_read_lock_nesting && 87 if (t->rcu_read_lock_nesting &&
88 (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { 88 (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
89 WARN_ON_ONCE(cpu != smp_processor_id());
89 90
90 /* Possibly blocking in an RCU read-side critical section. */ 91 /* Possibly blocking in an RCU read-side critical section. */
91 rdp = rcu_preempt_state.rda[cpu]; 92 rdp = rcu_preempt_state.rda[cpu];
@@ -103,7 +104,11 @@ static void rcu_preempt_qs(int cpu)
103 * state for the current grace period), then as long 104 * state for the current grace period), then as long
104 * as that task remains queued, the current grace period 105 * as that task remains queued, the current grace period
105 * cannot end. 106 * cannot end.
107 *
108 * But first, note that the current CPU must still be
109 * on line!
106 */ 110 */
111 WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);
107 phase = !(rnp->qsmask & rdp->grpmask) ^ (rnp->gpnum & 0x1); 112 phase = !(rnp->qsmask & rdp->grpmask) ^ (rnp->gpnum & 0x1);
108 list_add(&t->rcu_node_entry, &rnp->blocked_tasks[phase]); 113 list_add(&t->rcu_node_entry, &rnp->blocked_tasks[phase]);
109 smp_mb(); /* Ensure later ctxt swtch seen after above. */ 114 smp_mb(); /* Ensure later ctxt swtch seen after above. */
@@ -259,6 +264,18 @@ static void rcu_print_task_stall(struct rcu_node *rnp)
259#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ 264#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
260 265
261/* 266/*
267 * Check that the list of blocked tasks for the newly completed grace
268 * period is in fact empty. It is a serious bug to complete a grace
269 * period that still has RCU readers blocked! This function must be
270 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
271 * must be held by the caller.
272 */
273static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
274{
275 WARN_ON_ONCE(!list_empty(&rnp->blocked_tasks[rnp->gpnum & 0x1]));
276}
277
278/*
262 * Check for preempted RCU readers for the specified rcu_node structure. 279 * Check for preempted RCU readers for the specified rcu_node structure.
263 * If the caller needs a reliable answer, it must hold the rcu_node's 280 * If the caller needs a reliable answer, it must hold the rcu_node's
264 * >lock. 281 * >lock.
@@ -451,6 +468,14 @@ static void rcu_print_task_stall(struct rcu_node *rnp)
451#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ 468#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
452 469
453/* 470/*
471 * Because there is no preemptable RCU, there can be no readers blocked,
472 * so there is no need to check for blocked tasks.
473 */
474static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
475{
476}
477
478/*
454 * Because preemptable RCU does not exist, there are never any preempted 479 * Because preemptable RCU does not exist, there are never any preempted
455 * RCU readers. 480 * RCU readers.
456 */ 481 */