path: root/kernel/locking
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authorPeter Zijlstra <peterz@infradead.org>2014-09-30 15:26:00 +0200
committerIngo Molnar <mingo@kernel.org>2014-10-03 06:09:30 +0200
commit8acd91e8620836a56ff62028ed28ba629f2881a0 (patch)
tree4a95b0d1a41b75f6ad4cd8a6c59dcdb9268d1e4b /kernel/locking
parentdebfab74e453f079cd8b12b0604387a8c510ef3a (diff)
locking/lockdep: Revert qrwlock recusive stuff
Commit f0bab73cb539 ("locking/lockdep: Restrict the use of recursive read_lock() with qrwlock") changed lockdep to try and conform to the qrwlock semantics which differ from the traditional rwlock semantics. In particular qrwlock is fair outside of interrupt context, but in interrupt context readers will ignore all fairness. The problem modeling this is that read and write side have different lock state (interrupts) semantics but we only have a single representation of these. Therefore lockdep will get confused, thinking the lock can cause interrupt lock inversions. So revert it for now; the old rwlock semantics were already imperfectly modeled and the qrwlock extra won't fit either. If we want to properly fix this, I think we need to resurrect the work by Gautham did a few years ago that split the read and write state of locks: http://lwn.net/Articles/332801/ FWIW the locking selftest that would've failed (and was reported by Borislav earlier) is something like: RL(X1); /* IRQ-ON */ LOCK(A); UNLOCK(A); RU(X1); IRQ_ENTER(); RL(X1); /* IN-IRQ */ RU(X1); IRQ_EXIT(); At which point it would report that because A is an IRQ-unsafe lock we can suffer the following inversion: CPU0 CPU1 lock(A) lock(X1) lock(A) <IRQ> lock(X1) And this is 'wrong' because X1 can recurse (assuming the above lock are in fact read-lock) but lockdep doesn't know about this. Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Waiman Long <Waiman.Long@hp.com> Cc: ego@linux.vnet.ibm.com Cc: bp@alien8.de Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Link: http://lkml.kernel.org/r/20140930132600.GA7444@worktop.programming.kicks-ass.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/locking')
1 files changed, 0 insertions, 6 deletions
diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 420ba685c4e5..88d0d4420ad2 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3597,12 +3597,6 @@ void lock_acquire(struct lockdep_map *lock, unsigned int subclass,
- /*
- * 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,

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