Messages in this thread | | | Date | Wed, 20 Mar 2013 11:38:21 -0400 | From | Rik van Riel <> | Subject | Re: [PATCH v2 4/4] ipc: sem: do not hold ipc lock more than necessary |
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On 03/20/2013 10:27 AM, Rik van Riel wrote: > On 03/05/2013 04:36 AM, Davidlohr Bueso wrote: > >> @@ -1476,8 +1539,8 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct >> sembuf __user *, tsops, >> queue.sleeper = current; >> >> sleep_again: >> - current->state = TASK_INTERRUPTIBLE; >> sem_unlock(sma); >> + current->state = TASK_INTERRUPTIBLE; >> >> if (timeout) >> jiffies_left = schedule_timeout(jiffies_left); > > After modifying my test case to start with a semaphore value of 1 on > every semaphore, and do down followed by up (to have only one process > take each semaphore at a time), I started seeing lost wakeups and the > test case being stuck. > > I believe the change above is the cause of that issue. > > By unlocking before setting current->state to TASK_INTERRUPTIBLE, > there is a small window where the next lock holder can grab the > lock and wake us up, before we set ourselves to TASK_INTERRUPTIBLE > and go to sleep. > > I have reverted your change in my code and am building a test kernel > now. > > If things work, I'll clean up the whole patch series for a re-posting > today.
Half a billion semaphore operations later, I am pretty sure the above was the cause of the semaphore hangups we both observed :)
I am currently building a kernel with the cleaned up patch series I put together while building the previous test kernel.
If all goes well, expect a patch series after lunch...
-- All rights reversed
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