kevin/linux
1
Fork 0
Code

futex: abstract out a __futex_wake_mark() helper

Browse Source 
Move the unqueue and lock_ptr clear into a helper that futex_wake_mark()
calls. Add it to the public functions as well, in preparation for using
it outside the core futex code.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2023-07-12 09:14:52 -06:00
parent 12a4be50af
commit e52c43403c
2 changed files with 24 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
kernel/futex/futex.h
View File

@ -219,6 +219,7 @@ extern int futex_wait_setup(u32 __user *uaddr, u32 val, unsigned int flags,
struct futex_q *q, struct futex_hash_bucket **hb);
extern void futex_wait_queue(struct futex_hash_bucket *hb, struct futex_q *q,
struct hrtimer_sleeper *timeout);
extern bool __futex_wake_mark(struct futex_q *q);
extern void futex_wake_mark(struct wake_q_head *wake_q, struct futex_q *q);
extern int fault_in_user_writeable(u32 __user *uaddr);

35
kernel/futex/waitwake.c
View File

@ -106,6 +106,24 @@
* double_lock_hb() and double_unlock_hb(), respectively.
*/
bool __futex_wake_mark(struct futex_q *q)
{
if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
return false;
__futex_unqueue(q);
/*
* The waiting task can free the futex_q as soon as q->lock_ptr = NULL
* is written, without taking any locks. This is possible in the event
* of a spurious wakeup, for example. A memory barrier is required here
* to prevent the following store to lock_ptr from getting ahead of the
* plist_del in __futex_unqueue().
*/
smp_store_release(&q->lock_ptr, NULL);
return true;
}
/*
* The hash bucket lock must be held when this is called.
* Afterwards, the futex_q must not be accessed. Callers
@ -116,19 +134,12 @@ void futex_wake_mark(struct wake_q_head *wake_q, struct futex_q *q)
{
struct task_struct *p = q->task;
if (WARN(q->pi_state || q->rt_waiter, "refusing to wake PI futex\n"))
return;
get_task_struct(p);
__futex_unqueue(q);
/*
* The waiting task can free the futex_q as soon as q->lock_ptr = NULL
* is written, without taking any locks. This is possible in the event
* of a spurious wakeup, for example. A memory barrier is required here
* to prevent the following store to lock_ptr from getting ahead of the
* plist_del in __futex_unqueue().
*/
smp_store_release(&q->lock_ptr, NULL);
if (!__futex_wake_mark(q)) {
put_task_struct(p);
return;
}
/*
* Queue the task for later wakeup for after we've released