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Treat mutex->owner as volatile

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When HAVE_MUTEX_OWNER is defined and we are directly accessing
mutex->owner treat is as volative with the ACCESS_ONCE() helper.
Without this you may get a stale cached value when accessing it
from different cpus.  This can result in incorrect behavior from
mutex_owned() and mutex_owner().  This is not a problem for the
!HAVE_MUTEX_OWNER case because in this case all the accesses
are covered by a spin lock which similarly gaurentees we will
not be accessing stale data.

Secondly, check CONFIG_SMP before allowing access to mutex->owner.
I see that for non-SMP setups the kernel does not track the owner
so we cannot rely on it.

Thirdly, check CONFIG_MUTEX_DEBUG when this is defined and the
HAVE_MUTEX_OWNER is defined surprisingly the mutex->owner will
not be cleared on mutex_exit().  When this is the case the SPL
needs to make sure to do it to ensure MUTEX_HELD() behaves as
expected or you will certainly assert in mutex_destroy().

Finally, improve the mutex regression tests.  For mutex_owned() we
now minimally check that it behaves correctly when checked from the
owner thread or the non-owner thread.  This subtle behaviour has bit
me before and I'd like to catch it early next time if it reappears.

As for mutex_owned() regression test additonally verify that
mutex->owner is always cleared on mutex_exit().
This commit is contained in:
Brian Behlendorf
2010-06-28 12:48:20 -07:00
parent 616df2dd8b
commit ede0bdffb6
2 changed files with 116 additions and 22 deletions
Download Patch File Download Diff File Expand all files Collapse all files
include/sys/mutex.h
+28 -10
View File
@@ -34,20 +34,29 @@ typedef enum {
MUTEX_ADAPTIVE = 2
} kmutex_type_t;
#ifdef HAVE_MUTEX_OWNER
#if defined(HAVE_MUTEX_OWNER) && defined(CONFIG_SMP)
typedef struct mutex kmutex_t;
static inline kthread_t *
mutex_owner(kmutex_t *mp)
{
if (mp->owner)
return (mp->owner)->task;
struct thread_info *owner;
owner = ACCESS_ONCE(mp->owner);
if (owner)
return owner->task;
return NULL;
}
#define mutex_owned(mp) (mutex_owner(mp) == current)
#define MUTEX_HELD(mp) mutex_owned(mp)
static inline int
mutex_owned(kmutex_t *mp)
{
return (ACCESS_ONCE(mp->owner) == current_thread_info());
}
#define MUTEX_HELD(mp) mutex_owned(mp)
#undef mutex_init
#define mutex_init(mp, name, type, ibc) \
({ \
@@ -60,13 +69,22 @@ mutex_owner(kmutex_t *mp)
#undef mutex_destroy
#define mutex_destroy(mp) \
({ \
VERIFY(!MUTEX_HELD(mp)); \
VERIFY3P(mutex_owner(mp), ==, NULL); \
})
#define mutex_tryenter(mp) mutex_trylock(mp)
#define mutex_enter(mp) mutex_lock(mp)
#define mutex_exit(mp) mutex_unlock(mp)
#define mutex_tryenter(mp) mutex_trylock(mp)
#define mutex_enter(mp) mutex_lock(mp)
/* mutex->owner is not cleared when CONFIG_DEBUG_MUTEXES is set */
#ifdef CONFIG_DEBUG_MUTEXES
# define mutex_exit(mp) \
({ \
(mp)->owner = NULL; \
mutex_unlock(mp); \
})
#else
# define mutex_exit(mp) mutex_unlock(mp)
#endif /* CONFIG_DEBUG_MUTEXES */
#ifdef HAVE_GPL_ONLY_SYMBOLS
# define mutex_enter_nested(mp, sc) mutex_lock_nested(mp, sc)
@@ -151,7 +169,7 @@ mutex_owner(kmutex_t *mp)
#undef mutex_destroy
#define mutex_destroy(mp) \
({ \
VERIFY(!MUTEX_HELD(mp)); \
VERIFY3P(mutex_owner(mp), ==, NULL); \
})
#define mutex_tryenter(mp) \