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locking/mutex: Expose __mutex_owner()

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Implementing proxy execution requires that scheduler code be able to
identify the current owner of a mutex. Expose __mutex_owner() for
this purpose (alone!). Includes a null mutex check, so that users
of the function can be simplified.

[Removed the EXPORT_SYMBOL]
[jstultz: Reworked per Peter's suggestions]
Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Connor O'Brien <connoro@google.com>
Signed-off-by: John Stultz <jstultz@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Metin Kaya <metin.kaya@arm.com>
Reviewed-by: Valentin Schneider <vschneid@redhat.com>
Tested-by: K Prateek Nayak <kprateek.nayak@amd.com>
Tested-by: Metin Kaya <metin.kaya@arm.com>
Link: https://lore.kernel.org/r/20241009235352.1614323-4-jstultz@google.com
This commit is contained in:
Juri Lelli 2024-10-09 16:53:36 -07:00 committed by Peter Zijlstra
parent 5ec58525a1
commit 3a9320ecb0
2 changed files with 27 additions and 25 deletions
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25
kernel/locking/mutex.c
View File

@ -56,31 +56,6 @@ __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
}
EXPORT_SYMBOL(__mutex_init);
/*
* @owner: contains: 'struct task_struct *' to the current lock owner,
* NULL means not owned. Since task_struct pointers are aligned at
* at least L1_CACHE_BYTES, we have low bits to store extra state.
*
* Bit0 indicates a non-empty waiter list; unlock must issue a wakeup.
* Bit1 indicates unlock needs to hand the lock to the top-waiter
* Bit2 indicates handoff has been done and we're waiting for pickup.
*/
#define MUTEX_FLAG_WAITERS 0x01
#define MUTEX_FLAG_HANDOFF 0x02
#define MUTEX_FLAG_PICKUP 0x04
#define MUTEX_FLAGS 0x07
/*
* Internal helper function; C doesn't allow us to hide it :/
*
* DO NOT USE (outside of mutex code).
*/
static inline struct task_struct *__mutex_owner(struct mutex *lock)
{
return (struct task_struct *)(atomic_long_read(&lock->owner) & ~MUTEX_FLAGS);
}
static inline struct task_struct *__owner_task(unsigned long owner)
{
return (struct task_struct *)(owner & ~MUTEX_FLAGS);

27
kernel/locking/mutex.h
View File

@ -20,6 +20,33 @@ struct mutex_waiter {
#endif
};
/*
* @owner: contains: 'struct task_struct *' to the current lock owner,
* NULL means not owned. Since task_struct pointers are aligned at
* at least L1_CACHE_BYTES, we have low bits to store extra state.
*
* Bit0 indicates a non-empty waiter list; unlock must issue a wakeup.
* Bit1 indicates unlock needs to hand the lock to the top-waiter
* Bit2 indicates handoff has been done and we're waiting for pickup.
*/
#define MUTEX_FLAG_WAITERS 0x01
#define MUTEX_FLAG_HANDOFF 0x02
#define MUTEX_FLAG_PICKUP 0x04
#define MUTEX_FLAGS 0x07
/*
* Internal helper function; C doesn't allow us to hide it :/
*
* DO NOT USE (outside of mutex & scheduler code).
*/
static inline struct task_struct *__mutex_owner(struct mutex *lock)
{
if (!lock)
return NULL;
return (struct task_struct *)(atomic_long_read(&lock->owner) & ~MUTEX_FLAGS);
}
#ifdef CONFIG_DEBUG_MUTEXES
extern void debug_mutex_lock_common(struct mutex *lock,
struct mutex_waiter *waiter);