linux-kernel - [tip:x86/urgent] x86/fpu: Drop_fpu() should not assume that tsk equals current

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Message-ID: <tip-f4c3686386393c120710dd34df2a74183ab805fd@git.kernel.org>
Date:	Mon, 16 Mar 2015 05:07:31 -0700
From:	tip-bot for Oleg Nesterov <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	priikone@....fi, stable@...r.kernel.org, tglx@...utronix.de,
	torvalds@...ux-foundation.org, fenghua.yu@...el.com, bp@...en8.de,
	luto@...capital.net, linux-kernel@...r.kernel.org,
	dave.hansen@...el.com, sbsiddha@...il.com, hpa@...or.com,
	quentin.casasnovas@...cle.com, mingo@...nel.org, riel@...hat.com,
	bp@...e.de, oleg@...hat.com
Subject: [tip:x86/urgent] x86/fpu: Drop_fpu()
  should not assume that tsk equals current

Commit-ID:  f4c3686386393c120710dd34df2a74183ab805fd
Gitweb:     http://git.kernel.org/tip/f4c3686386393c120710dd34df2a74183ab805fd
Author:     Oleg Nesterov <oleg@...hat.com>
AuthorDate: Fri, 13 Mar 2015 09:53:10 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 13 Mar 2015 12:44:29 +0100

x86/fpu: Drop_fpu() should not assume that tsk equals current

drop_fpu() does clear_used_math() and usually this is correct
because tsk == current.

However switch_fpu_finish()->restore_fpu_checking() is called before
__switch_to() updates the "current_task" variable. If it fails,
we will wrongly clear the PF_USED_MATH flag of the previous task.

So use clear_stopped_child_used_math() instead.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
Signed-off-by: Borislav Petkov <bp@...e.de>
Reviewed-by: Rik van Riel <riel@...hat.com>
Cc: <stable@...r.kernel.org>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Fenghua Yu <fenghua.yu@...el.com>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Pekka Riikonen <priikone@....fi>
Cc: Quentin Casasnovas <quentin.casasnovas@...cle.com>
Cc: Suresh Siddha <sbsiddha@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/20150309171041.GB11388@redhat.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/include/asm/fpu-internal.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/fpu-internal.h b/arch/x86/include/asm/fpu-internal.h
index 0dbc082..72ba21a 100644
--- a/arch/x86/include/asm/fpu-internal.h
+++ b/arch/x86/include/asm/fpu-internal.h
@@ -370,7 +370,7 @@ static inline void drop_fpu(struct task_struct *tsk)
 	preempt_disable();
 	tsk->thread.fpu_counter = 0;
 	__drop_fpu(tsk);
-	clear_used_math();
+	clear_stopped_child_used_math(tsk);
 	preempt_enable();
 }
 
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