Re: [PATCH] ipc/sem.c: fix update sem_otime when calling sem_op insemaphore initialization

[Manfred Spraul]

Hi all,

On 09/22/2013 10:26 AM, Mike Galbraith wrote:
> On Sun, 2013-09-22 at 10:17 +0200, Mike Galbraith wrote:
> > On Sun, 2013-09-22 at 10:11 +0800, Jia He wrote:
> > > In commit 0a2b9d4c,the update of semaphore's sem_otime(last semop time)
> > > was removed because he wanted to move setting sem->sem_otime to one
> > > place. But after that, the initial semop() will not set the otime
> > > because its sem_op value is 0(in semtimedop,will not change
> > > otime if alter == 1).
> > >
> > > the error case:
> > > process_a(server)       process_b(client)
> > > semget()
> > > semctl(SETVAL)
> > > semop()
> > >                          semget()
> > >                          setctl(IP_STAT)
> > >                          for(;;) {               <--not successful here
> > >                            check until sem_otime > 0
> > >                          }
Good catch:
Since commit 0a2b9d4c, wait-for-zero semops do not update sem_otime anymore.

Let's reverse that part of my commit and move the update of sem_otime 
back into perform_atomic_semop().

Jia: If perform_atomic_semop() updates sem_otime, then the update in 
do_smart_update() is not necessary anymore.
Thus the whole logic with passing arround "semop_completed" can be 
removed, too.
Are you interested in writing that patch?


> > Why not..
> (pokes evolution's don't-munge-me button)
>
> ipc,sem: Create semaphores with plausible sem_otime.
Mike: no, your patch makes it worse:
- wait-for-zero semops still don't update sem_otime
- sem_otime is initialized to sem_ctime. That's not mentioned in the 
sysv standard.

--
    Manfred
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