linux-kernel - [PATCH 0/1] x86/fpu: math_state_restore() should not blindly disable irqs

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Message-ID: <20150305195127.GA12657@redhat.com>
Date:	Thu, 5 Mar 2015 20:51:27 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Dave Hansen <dave.hansen@...el.com>, Borislav Petkov <bp@...e.de>,
	Ingo Molnar <mingo@...nel.org>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Pekka Riikonen <priikone@....fi>,
	Rik van Riel <riel@...hat.com>,
	Suresh Siddha <sbsiddha@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Yu, Fenghua" <fenghua.yu@...el.com>,
	Quentin Casasnovas <quentin.casasnovas@...cle.com>
Subject: [PATCH 0/1] x86/fpu: math_state_restore() should not blindly
	disable irqs

On 03/05, Oleg Nesterov wrote:
>
> And this also means I have another off-topic fix for 4.0/stable, will
> send a patch in a minute...

I knew about this problem, but I didn't realize that restore_sigcontext()
can call a sleeping function after math_state_restore(). So I was going
to fix this later, because we need a lot more cleanups in these paths.

But it turns out, it is trivial to trigger the "BUG: sleeping function
called from invalid context" warning, see the test-case I sent to Dave.

To avoid the confusion, this has nothing to do with the problems we
discuss in other threads, or with the recent changes in tip/x86/fpu.

The patch is horrible, yes. But simple, and math_state_restore/init_fpu
are already horrible and need the cleanups. Hopefully I'll send them "soon".

Oleg.

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