Minki/linux
1
0
Fork 1
mirror of https://github.com/torvalds/linux.git synced 2024-11-14 08:02:07 +00:00
Code Issues Packages Projects Releases Wiki Activity

locking/mutexes/mcs: Correct barrier usage

Browse Source 
This patch corrects the way memory barriers are used in the MCS lock
with smp_load_acquire and smp_store_release fucnctions.  The previous
barriers could leak critical sections if mcs lock is used by itself.
It is not a problem when mcs lock is embedded in mutex but will be an
issue when the mcs_lock is used elsewhere.

The patch removes the incorrect barriers and put in correct
barriers with the pair of functions smp_load_acquire and smp_store_release.

Suggested-by: Michel Lespinasse <walken@google.com>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Waiman Long <Waiman.Long@hp.com>
Signed-off-by: Jason Low <jason.low2@hp.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1390347353.3138.62.camel@schen9-DESK
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Waiman Long 2014-01-21 15:35:53 -08:00 committed by Ingo Molnar
parent 270750dbc1
commit aff7385b5a
1 changed files with 13 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

18
kernel/locking/mutex.c
View File

@ -136,9 +136,12 @@ void mspin_lock(struct mspin_node **lock, struct mspin_node *node)
return; return;
} }
ACCESS_ONCE(prev->next) = node; ACCESS_ONCE(prev->next) = node;
smp_wmb(); /*
/* Wait until the lock holder passes the lock down */ * Wait until the lock holder passes the lock down.
while (!ACCESS_ONCE(node->locked)) * Using smp_load_acquire() provides a memory barrier that
* ensures subsequent operations happen after the lock is acquired.
*/
while (!(smp_load_acquire(&node->locked)))
arch_mutex_cpu_relax(); arch_mutex_cpu_relax();
} }
@ -156,8 +159,13 @@ static void mspin_unlock(struct mspin_node **lock, struct mspin_node *node)
while (!(next = ACCESS_ONCE(node->next))) while (!(next = ACCESS_ONCE(node->next)))
arch_mutex_cpu_relax(); arch_mutex_cpu_relax();
} }
ACCESS_ONCE(next->locked) = 1; /*
smp_wmb(); * Pass lock to next waiter.
* smp_store_release() provides a memory barrier to ensure
* all operations in the critical section has been completed
* before unlocking.
*/
smp_store_release(&next->locked, 1);
} }
/* /*