On Sun, 2014-05-25 at 20:21 +0200, Manfred Spraul wrote:
> The actual Linux implementation for semctl(GETNCNT) and semctl(GETZCNT)
> always (since 0.99.10) reported a thread as sleeping on all semaphores
> that are listed in the semop() call.
> The documented behavior (both in the Linux man page and in the Single Unix
> Specification) is that a task should be reported on exactly one semaphore:
> The semaphore that caused the thread to got to sleep.
>
> This patch adds a printk_once() that is triggered if a thread hits
> the relevant case.
>
> Signed-off-by: Manfred Spraul <manf...@colorfullife.com>
> Cc: Davidlohr Bueso <davidlohr.bu...@hp.com>
Acked-by: Davidlohr Bueso <davidl...@hp.com>
With some minor suggestions below.
> Cc: Michael Kerrisk <mtk.manpa...@gmail.com>
> ---
> ipc/sem.c | 12 ++++++++++++
> 1 file changed, 12 insertions(+)
>
> diff --git a/ipc/sem.c b/ipc/sem.c
> index 9106321..3cc2f7b6 100644
> --- a/ipc/sem.c
> +++ b/ipc/sem.c
> @@ -1000,6 +1000,18 @@ static int check_qop(struct sem_array *sma, int
> semnum, struct sem_queue *q,
> {
> struct sembuf *sop = q->blocking;
>
> + /*
> + * Linux always (since 0.99.10) reported a task as sleeping on all
> + * semaphores. This violates SUS, therefore it was changed to the
> + * standard compliant behavior.
> + * Give the administrators a chance to notice that an application
> + * might misbehave because it relies on the Linux behavior.
> + */
> + printk_once(KERN_INFO "semctl(GETNCNT/GETZCNT) is since 3.16 Single " \
> + "Unix Specification compliant.\n" \
> + "The task %d triggered the difference, " \
^^ %u (->pid is unsigned)
It would also be useful to print ->comm. I hate having to lookup the
process name with just the pid.
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