diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2017-01-11 14:17:48 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2017-01-14 11:14:38 +0100 |
| commit | e274795ea7b7caa0fd74ef651594382a69e2a951 (patch) | |
| tree | 345b942f86040c9361e1a2b0bc45f58f7b48bb19 /kernel/fork.c | |
| parent | 52b94129f274937e4c25dd17b76697664a3c43c9 (diff) | |
| download | linux-e274795ea7b7caa0fd74ef651594382a69e2a951.tar.bz2 | |
locking/mutex: Fix mutex handoff
While reviewing the ww_mutex patches, I noticed that it was still
possible to (incorrectly) succeed for (incorrect) code like:
mutex_lock(&a);
mutex_lock(&a);
This was possible if the second mutex_lock() would block (as expected)
but then receive a spurious wakeup. At that point it would find itself
at the front of the queue, request a handoff and instantly claim
ownership and continue, since owner would point to itself.
Avoid this scenario and simplify the code by introducing a third low
bit to signal handoff pickup. So once we request handoff, unlock
clears the handoff bit and sets the pickup bit along with the new
owner.
This also removes the need for the .handoff argument to
__mutex_trylock(), since that becomes superfluous with PICKUP.
In order to guarantee enough low bits, ensure task_struct alignment is
at least L1_CACHE_BYTES (which seems a good ideal regardless).
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 9d659ae14b54 ("locking/mutex: Add lock handoff to avoid starvation")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/fork.c')
| -rw-r--r-- | kernel/fork.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/kernel/fork.c b/kernel/fork.c index 11c5c8ab827c..a90510d0bbf8 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -432,11 +432,13 @@ void __init fork_init(void) int i; #ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR #ifndef ARCH_MIN_TASKALIGN -#define ARCH_MIN_TASKALIGN L1_CACHE_BYTES +#define ARCH_MIN_TASKALIGN 0 #endif + int align = min_t(int, L1_CACHE_BYTES, ARCH_MIN_TASKALIGN); + /* create a slab on which task_structs can be allocated */ task_struct_cachep = kmem_cache_create("task_struct", - arch_task_struct_size, ARCH_MIN_TASKALIGN, + arch_task_struct_size, align, SLAB_PANIC|SLAB_NOTRACK|SLAB_ACCOUNT, NULL); #endif |