From: Oleg Nesterov <oleg@redhat.com> mainline inclusion from mainline-5.7-rc1 commit 6fb614920b38bbf3c1c7fcd944c6d9b5d746103d category: feature bugzilla: https://bugzilla.openeuler.org/show_bug.cgi?id=27 CVE: NA --------------------------- As Peter pointed out, task_work() can avoid ->pi_lock and cmpxchg() if task->task_works == NULL && !PF_EXITING. And in fact the only reason why task_work_run() needs ->pi_lock is the possible race with task_work_cancel(), we can optimize this code and make the locking more clear. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Jens Axboe <axboe@kernel.dk> Signed-off-by: yangerkun <yangerkun@huawei.com> Reviewed-by: zhangyi (F) <yi.zhang@huawei.com> Signed-off-by: Cheng Jian <cj.chengjian@huawei.com> --- kernel/task_work.c | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-) diff --git a/kernel/task_work.c b/kernel/task_work.c index 0fef395662a6..825f28259a19 100644 --- a/kernel/task_work.c +++ b/kernel/task_work.c @@ -97,16 +97,26 @@ void task_work_run(void) * work->func() can do task_work_add(), do not set * work_exited unless the list is empty. */ - raw_spin_lock_irq(&task->pi_lock); do { + head = NULL; work = READ_ONCE(task->task_works); - head = !work && (task->flags & PF_EXITING) ? - &work_exited : NULL; + if (!work) { + if (task->flags & PF_EXITING) + head = &work_exited; + else + break; + } } while (cmpxchg(&task->task_works, work, head) != work); - raw_spin_unlock_irq(&task->pi_lock); if (!work) break; + /* + * Synchronize with task_work_cancel(). It can not remove + * the first entry == work, cmpxchg(task_works) must fail. + * But it can remove another entry from the ->next list. + */ + raw_spin_lock_irq(&task->pi_lock); + raw_spin_unlock_irq(&task->pi_lock); do { next = work->next; -- 2.25.1