Date: Thu, 8 May 2014 19:30:53 -0700 From: hiren panchasara <hiren.panchasara@gmail.com> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-stable@freebsd.org Subject: Re: stable/10 panic Message-ID: <CALCpEUEt=SOsMtePYnt%2BPDHijdHaUJExoiFu%2BBx4Dj7DPPkxaw@mail.gmail.com> In-Reply-To: <201405081219.27412.jhb@freebsd.org> References: <1398097892.1101.6.camel@powernoodle.corp.yahoo.com> <201405071431.38812.jhb@freebsd.org> <CALCpEUGxd8KFbjBaXh-N0pzp5YjG6_xqQdXc%2B2Uu%2BvNSA8hXhw@mail.gmail.com> <201405081219.27412.jhb@freebsd.org>
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[trimming a lot of things]
On Thu, May 8, 2014 at 9:19 AM, John Baldwin <jhb@freebsd.org> wrote:
> On Thursday, May 08, 2014 12:39:20 am hiren panchasara wrote:
>> On Wed, May 7, 2014 at 11:31 AM, John Baldwin <jhb@freebsd.org> wrote:
>> >> 1639. /*
>> >> 1640. * shutdown the pipe
>> >> 1641. */
>> >> 1642. static void
>> >> 1643. pipeclose(cpipe)
>> >> 1644. struct pipe *cpipe;
>> >> 1645. {
>> >> 1646. struct pipepair *pp;
>> >> 1647. struct pipe *ppipe;
>> >> 1648.
>> >> 1649. KASSERT(cpipe != NULL, ("pipeclose: cpipe == NULL"));
>> >> 1650.
>> >> 1651. PIPE_LOCK(cpipe);
>> >> 1652. pipelock(cpipe, 0);
>> >> 1653. pp = cpipe->pipe_pair;
>> >> 1654.
>> >> 1655. pipeselwakeup(cpipe);
>> >>
>> >> pipeclose() gets called from pipe_dtor()
>> >
>> > Eh, so it seems like pipeclose() has been called twice on the same pipe which
>> > should never happen.
>>
>> How did you get to that conclusion?
>
> The pipe's state (cpipe->pipe_present) is set to 3 (PIPE_FINALIZED) which only
> happens at bottom of pipeclose(cpipe). However, in your panic, you are dying
> at the start of pipeclose() when cpipe's state should be the initial state
> still. That is also consistent with the panic as the knlist for the pipe has
> already been destroyed (which happens later in pipeclose()) and that is what
> zero's the lock fields in knlist causing the actual fault in knote().
>
Makes sense.
>
> Eh, kgdb should be deterministic given a specific kernel and core file.
> That is to say, above 'f 11', 'p *dpipe' did something, but here it
> did not. Are you running kgdb on the same core or a different one?
>
Just to end the confusion:
http://people.freebsd.org/~hiren/pipeclose_panic_stable10.txt
>
>> (kgdb) p *fip
>> $2 = {fi_pipe = 0xffffffff80c96b7e, fi_readers = -2129533840,
>> fi_writers = -8782327094120}
>
> The readers/writers counts here are garbage. I probably wouldn't trust
> the fi_pipe value either. Would be nice to know if the various pointers
> line up. Also, I would expect a FIFO to have the 'NAMED' flag set and
> thus for pipe_peer to be a different pipe (not itself), but I believe that
> was not true from the earlier posts.
My reading of code says named pipe doesn't have different pipe for pipe_peer?
sys/kern/sys_pipe.c
#define PIPE_PEER(pipe) \
(((pipe)->pipe_state & PIPE_NAMED) ? (pipe) : ((pipe)->pipe_peer))
cheers,
Hiren
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