locking/lockdep: Restrict the use of recursive read_lock() with qrwlock

Unlike the original unfair rwlock implementation, queued rwlock
will grant lock according to the chronological sequence of the lock
requests except when the lock requester is in the interrupt context.
Consequently, recursive read_lock calls will now hang the process if
there is a write_lock call somewhere in between the read_lock calls.

This patch updates the lockdep implementation to look for recursive
read_lock calls. A new read state (3) is used to mark those read_lock
call that cannot be recursively called except in the interrupt
context. The new read state does exhaust the 2 bits available in
held_lock:read bit field. The addition of any new read state in the
future may require a redesign of how all those bits are squeezed
together in the held_lock structure.

Signed-off-by: Waiman Long <Waiman.Long@hp.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Maarten Lankhorst <maarten.lankhorst@canonical.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Scott J Norton <scott.norton@hp.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1407345722-61615-2-git-send-email-Waiman.Long@hp.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 6 insertions, 0 deletions

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 88d0d4420ad2..420ba685c4e5 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3597,6 +3597,12 @@ void lock_acquire(struct lockdep_map *lock, unsigned int subclass,
         raw_local_irq_save(flags);
         check_flags(flags);
 
+        /*
+         * An interrupt recursive read in interrupt context can be considered
+         * to be the same as a recursive read from checking perspective.
+         */
+        if ((read == 3) && in_interrupt())
+                read = 2;
         current->lockdep_recursion = 1;
         trace_lock_acquire(lock, subclass, trylock, read, check, nest_lock, ip);
         __lock_acquire(lock, subclass, trylock, read, check,