linux-kernel - Re: 3.14-rc2 XFS backtrace because irqs

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Message-ID: <CA+55aFywwx0Q8xK2GJiRJ+FV7PQEKoBRxDUxW4052FVyd5XOpg@mail.gmail.com>
Date:	Wed, 12 Feb 2014 12:13:19 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	Dave Chinner <david@...morbit.com>, Dave Jones <davej@...hat.com>,
	Eric Sandeen <sandeen@...deen.net>,
	Linux Kernel <linux-kernel@...r.kernel.org>, xfs@....sgi.com
Subject: Re: 3.14-rc2 XFS backtrace because irqs_disabled.

On Wed, Feb 12, 2014 at 3:39 AM, Al Viro <viro@...iv.linux.org.uk> wrote:
> On Tue, Feb 11, 2014 at 10:28:12PM -0800, Linus Torvalds wrote:
>
>> It looks like just "do_signal()" has a stack frame that is about 230
>> bytes even under normal circumstancs (largely due to "struct ksignal"
>> - which in turn is largely due to the insane 128-byte padding in
>> siginfo_t). Add a few other frames in there, and I guess that if it
>> was close before, the coredump path just makes it go off.
>
> We could, in principle, put it into task_struct and make get_signal()
> return its address - do_signal() is called only in the code that does
> assorted returns to userland...

We have better uses for random buffers in "struct task_struct", I'd
hate to put a siginfo_t there.

The thing is, siginfo_t has that idiotic 128-byte area, but it's all
"for future expansion". I think it's some damn glibc disease - we've
seen these kinds of insane paddings before.

The actual *useful* part of siginfo_t is on the order of 32 bytes. If that.

Sad.

                Linus
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