diff options
| author | Xie Yongji <xieyongji@baidu.com> | 2018-11-29 20:50:30 +0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-03-05 17:58:00 +0100 |
| commit | 726152d423685a4ae266f360e8bb32567c19f522 (patch) | |
| tree | f737b23b0b0f5d05ae83edf1346e0f3bafbbf3ec /kernel/locking | |
| parent | f618b90b11fc45efd13a159f628f27f06ebb8184 (diff) | |
locking/rwsem: Fix (possible) missed wakeup
[ Upstream commit e158488be27b157802753a59b336142dc0eb0380 ]
Because wake_q_add() can imply an immediate wakeup (cmpxchg failure
case), we must not rely on the wakeup being delayed. However, commit:
e38513905eea ("locking/rwsem: Rework zeroing reader waiter->task")
relies on exactly that behaviour in that the wakeup must not happen
until after we clear waiter->task.
[ peterz: Added changelog. ]
Signed-off-by: Xie Yongji <xieyongji@baidu.com>
Signed-off-by: Zhang Yu <zhangyu31@baidu.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: e38513905eea ("locking/rwsem: Rework zeroing reader waiter->task")
Link: https://lkml.kernel.org/r/1543495830-2644-1-git-send-email-xieyongji@baidu.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Diffstat (limited to 'kernel/locking')
| -rw-r--r-- | kernel/locking/rwsem-xadd.c | 11 |
1 files changed, 9 insertions, 2 deletions
diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c index a90336779375..c75017326c37 100644 --- a/kernel/locking/rwsem-xadd.c +++ b/kernel/locking/rwsem-xadd.c @@ -198,15 +198,22 @@ static void __rwsem_mark_wake(struct rw_semaphore *sem, woken++; tsk = waiter->task; - wake_q_add(wake_q, tsk); + get_task_struct(tsk); list_del(&waiter->list); /* - * Ensure that the last operation is setting the reader + * Ensure calling get_task_struct() before setting the reader * waiter to nil such that rwsem_down_read_failed() cannot * race with do_exit() by always holding a reference count * to the task to wakeup. */ smp_store_release(&waiter->task, NULL); + /* + * Ensure issuing the wakeup (either by us or someone else) + * after setting the reader waiter to nil. + */ + wake_q_add(wake_q, tsk); + /* wake_q_add() already take the task ref */ + put_task_struct(tsk); } adjustment = woken * RWSEM_ACTIVE_READ_BIAS - adjustment; |