diff options
| author | Uros Bizjak <ubizjak@gmail.com> | 2022-08-23 17:26:32 +0200 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2022-09-11 21:55:10 -0700 |
| commit | 5fdfa161b2043001f82cbce49e87e8e9f581d510 (patch) | |
| tree | e3326441233ff70650de4244502dd08ea438cdd1 /kernel/task_work.c | |
| parent | 977bbf4385fc64986f22b024858071a35c481a8a (diff) | |
task_work: use try_cmpxchg in task_work_add, task_work_cancel_match and task_work_run
Use try_cmpxchg instead of cmpxchg (*ptr, old, new) == old in
task_work_add, task_work_cancel_match and task_work_run. x86 CMPXCHG
instruction returns success in ZF flag, so this change saves a compare
after cmpxchg (and related move instruction in front of cmpxchg).
Also, atomic_try_cmpxchg implicitly assigns old *ptr value to "old"
when cmpxchg fails, enabling further code simplifications.
The patch avoids extra memory read in case cmpxchg fails.
Link: https://lkml.kernel.org/r/20220823152632.4517-1-ubizjak@gmail.com
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'kernel/task_work.c')
| -rw-r--r-- | kernel/task_work.c | 16 |
1 files changed, 9 insertions, 7 deletions
diff --git a/kernel/task_work.c b/kernel/task_work.c index dff75bcde151..065e1ef8fc8d 100644 --- a/kernel/task_work.c +++ b/kernel/task_work.c @@ -47,12 +47,12 @@ int task_work_add(struct task_struct *task, struct callback_head *work, /* record the work call stack in order to print it in KASAN reports */ kasan_record_aux_stack(work); + head = READ_ONCE(task->task_works); do { - head = READ_ONCE(task->task_works); if (unlikely(head == &work_exited)) return -ESRCH; work->next = head; - } while (cmpxchg(&task->task_works, head, work) != head); + } while (!try_cmpxchg(&task->task_works, &head, work)); switch (notify) { case TWA_NONE: @@ -100,10 +100,12 @@ task_work_cancel_match(struct task_struct *task, * we raced with task_work_run(), *pprev == NULL/exited. */ raw_spin_lock_irqsave(&task->pi_lock, flags); - while ((work = READ_ONCE(*pprev))) { - if (!match(work, data)) + work = READ_ONCE(*pprev); + while (work) { + if (!match(work, data)) { pprev = &work->next; - else if (cmpxchg(pprev, work, work->next) == work) + work = READ_ONCE(*pprev); + } else if (try_cmpxchg(pprev, &work, work->next)) break; } raw_spin_unlock_irqrestore(&task->pi_lock, flags); @@ -151,16 +153,16 @@ void task_work_run(void) * work->func() can do task_work_add(), do not set * work_exited unless the list is empty. */ + work = READ_ONCE(task->task_works); do { head = NULL; - work = READ_ONCE(task->task_works); if (!work) { if (task->flags & PF_EXITING) head = &work_exited; else break; } - } while (cmpxchg(&task->task_works, work, head) != work); + } while (!try_cmpxchg(&task->task_works, &work, head)); if (!work) break; |