linux-kernel - Re: um: WARNING: at kernel/futex.c:786 __unqueue

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Message-ID: <AANLkTi=Z_yYkdwzO7TMs7nSMOXR9wn_7BxtKjOKgS5HL@mail.gmail.com>
Date:	Thu, 17 Mar 2011 15:27:29 +0100
From:	richard -rw- weinberger <richard.weinberger@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	laijs@...fujitsu.com, LKML <linux-kernel@...r.kernel.org>,
	user-mode-linux-devel@...ts.sourceforge.net, dvhart@...ux.intel.com
Subject: Re: um: WARNING: at kernel/futex.c:786 __unqueue_futex

On Thu, Mar 17, 2011 at 3:08 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Thu, 2011-03-17 at 13:25 +0100, richard -rw- weinberger wrote:
>> Lai,
>>
>> Your commit 2e12978a
>> (futex,plist: Pass the real head of the priority list to plist_del())
>> triggers gazillions warnings on User Mode Linux (x86, Linus' tree as of today):
>>
>> ------------[ cut here ]------------
>> WARNING: at kernel/futex.c:786 __unqueue_futex+0x12/0x16()
>> Modules linked in:
>> 27d4cce8:  [<081c13fe>] dump_stack+0x1c/0x20
>> 27d4cd00:  [<08071aa0>] warn_slowpath_common+0x49/0x5f
>> 27d4cd18:  [<08071acb>] warn_slowpath_null+0x15/0x19
>> 27d4cd28:  [<0808fdb8>] __unqueue_futex+0x12/0x16
>> 27d4cd38:  [<0808fef3>] futex_wait+0x137/0x1ed
>> 27d4cdd0:  [<080910c3>] do_futex+0x78/0x7c4
>> 27d4cedc:  [<080918e6>] sys_futex+0xd7/0xed
>> 27d4cf28:  [<0805abf6>] handle_syscall+0x7a/0x98
>> 27d4cf78:  [<080685d9>] userspace+0x2c9/0x370
>> 27d4cfe0:  [<08058be5>] fork_handler+0x53/0x5b
>> 27d4cffc:  [<00000000>] 0x0
>>
>> ---[ end trace ed7709f235f82328 ]---
>>
>> !spin_is_locked(q->lock_ptr) in the WARN_ON() at line 786
>> triggers the warnings.
>
> Crap, I bet you are running CONFIG_SMP=n. I'll test this. We may need to
> make that a WARN_ON_SMP().

BTW: When using WARN_ON_SMP() the if-statement in __unqueue_futex
will not longer work.

WARN_ON_SMP() is defined as "do { } while (0)" on non CONFIG_SMP systems.


> -- Steve
>
>>
>> I'm not sure whether this shows a bug within UML
>> or the WARN_ON() is wrong.
>>
>> What do you think?
>>
>
>
>

-- 
Thanks,
//richard
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