linux-kernel - Re: wait_even_interruptible_timeout(), signal, spin

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Message-ID: <AANLkTimnSAvy4JmNiEyrgA_wXDNC9FphneDhNhe8FY5D@mail.gmail.com>
Date:	Fri, 4 Jun 2010 07:13:00 -0500
From:	Shirish Pargaonkar <shirishpargaonkar@...il.com>
To:	Jeff Layton <jlayton@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: wait_even_interruptible_timeout(), signal, spin_lock() = system 
	hang

On Fri, Jun 4, 2010 at 6:51 AM, Jeff Layton <jlayton@...hat.com> wrote:
> On Fri, 28 May 2010 11:44:46 -0500
> Shirish Pargaonkar <shirishpargaonkar@...il.com> wrote:
>
>> After this sequence of calls, system hangs (smp, x86 box based with
>> .34 kernel), can ping only.
>> I have not been able to break in with Alt Sysrq t, working on that
>>
>>         rc = wait_event_interruptible_timeout(ses->server->response_q,
>>                         (midQ->midState != MID_REQUEST_SUBMITTED), timeout);
>>         if (rc < 0) {
>>                 cFYI(1, ("command 0x%x interrupted", midQ->command));
>>                 return -1;
>>         }
>>
>> and when function that invoking function after coming out with ERESTARTSYS
>> (I kill the command with Ctrl C) calls
>>  spin_lock(&GlobalMid_Lock);
>>
>> system hangs.  If I sleep before return -1 (e.g. msleep(1), no hang)
>>
>
> Sounds like a race of some sort, but could also be that msleep() is
> doing something (perhaps relating to the pending signal) that prevents
> the hang. Without some sort of clue as to what the box is hung on at
> the time there is no way to know.
>
>> I do not have to use wait_event_interruptible_timeout and no such problems with
>> wait_event_timeout, it is only when signal/interrupt is involved, I
>> run into this problem
>>
>> Any pointers/ideas what could be happening, would be really really appreciated.
>>
>
> No idea right offhand. I'd suggest getting a core or sysrq data and see
> what it's doing.
>
> --
> Jeff Layton <jlayton@...hat.com>
>

Jeff, Thanks.  The system hangs really hard. It does not respond to
Alt ScrLk  Ctrl ScrLk
key sequence at the text mode console i.e. nothing gets logged in
/var/log/messages.

Regards,

Shirish
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