* Re: Possible FPU context corruption w/ CONFIG_PREEMPT
2010-11-27 5:34 ` Brian Gerst
@ 2010-11-27 10:18 ` Tejun Heo
0 siblings, 0 replies; 3+ messages in thread
From: Tejun Heo @ 2010-11-27 10:18 UTC (permalink / raw)
To: Brian Gerst
Cc: lkml, Suresh Siddha, H. Peter Anvin, Robert Richter,
Dan Carpenter, Avi Kivity, Bernd Machenschalk,
Heinz-Bernd Eggenstein, Oliver Bock, the arch/x86 maintainers
Hey, Brian.
On 11/27/2010 06:34 AM, Brian Gerst wrote:
> On Fri, Nov 26, 2010 at 10:31 AM, Tejun Heo <tj@kernel.org> wrote:
>> Hello, guys.
>>
>> Heinz-Bernd Eggenstein reports a possible FPU context corruption w/
>> CONFIG_PREEMPT. Please take a look at the following forum post.
>>
>> http://einstein.phys.uwm.edu/forum_thread.php?id=8516
>>
>> openSUSE 11.3 desktop kernel which has CONFIG_PREEMPT set is
>> triggering SIGFPE while the default kernel w/o preemption works fine.
>> He also notes that a similar bug was fixed in 2008 by commit 06c38d5e
>> (x86-64: fix FPU corruption with signals and preemption) from Suresh.
>> Does it ring anyone's bell?
>>
>> Heinz, is there a simple procedure to reproduce the problem, or would
>> it be possible to lure you into bisection?
>
> This might be fixed by commit a4d4fbc7735bba6654b20f859135f9d3f8fe7f76
> (Disable preemption when using TS_USEDFPU).
Thanks for the pointer. Can someone please verify whether the
following patch fixes the issue? And, if so, this definitely should
go to -stable.
>From a4d4fbc7735bba6654b20f859135f9d3f8fe7f76 Mon Sep 17 00:00:00 2001
From: Brian Gerst <brgerst@gmail.com>
Date: Fri, 3 Sep 2010 21:17:12 -0400
Subject: [PATCH] x86-64, fpu: Disable preemption when using TS_USEDFPU
Consolidates code and fixes the below race for 64-bit.
commit 9fa2f37bfeb798728241cc4a19578ce6e4258f25
Author: torvalds <torvalds>
Date: Tue Sep 2 07:37:25 2003 +0000
Be a lot more careful about TS_USEDFPU and preemption
We had some races where we testecd (or set) TS_USEDFPU together
with sequences that depended on the setting (like clearing or
setting the TS flag in %cr0) and we could be preempted in between,
which screws up the FPU state, since preemption will itself change
USEDFPU and the TS flag.
This makes it a lot more explicit: the "internal" low-level FPU
functions ("__xxxx_fpu()") all require preemption to be disabled,
and the exported "real" functions will make sure that is the case.
One case - in __switch_to() - was switched to the non-preempt-safe
internal version, since the scheduler itself has already disabled
preemption.
BKrev: 3f5448b5WRiQuyzAlbajs3qoQjSobw
Signed-off-by: Brian Gerst <brgerst@gmail.com>
Acked-by: Pekka Enberg <penberg@kernel.org>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
LKML-Reference: <1283563039-3466-6-git-send-email-brgerst@gmail.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
---
arch/x86/include/asm/i387.h | 15 ---------------
arch/x86/kernel/process_64.c | 2 +-
2 files changed, 1 insertions(+), 16 deletions(-)
diff --git a/arch/x86/include/asm/i387.h b/arch/x86/include/asm/i387.h
index 88065e3..8b40a83 100644
--- a/arch/x86/include/asm/i387.h
+++ b/arch/x86/include/asm/i387.h
@@ -387,19 +387,6 @@ static inline void irq_ts_restore(int TS_state)
stts();
}
-#ifdef CONFIG_X86_64
-
-static inline void save_init_fpu(struct task_struct *tsk)
-{
- __save_init_fpu(tsk);
- stts();
-}
-
-#define unlazy_fpu __unlazy_fpu
-#define clear_fpu __clear_fpu
-
-#else /* CONFIG_X86_32 */
-
/*
* These disable preemption on their own and are safe
*/
@@ -425,8 +412,6 @@ static inline void clear_fpu(struct task_struct *tsk)
preempt_enable();
}
-#endif /* CONFIG_X86_64 */
-
/*
* i387 state interaction
*/
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 3d9ea53..b3d7a3a 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -424,7 +424,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
load_TLS(next, cpu);
/* Must be after DS reload */
- unlazy_fpu(prev_p);
+ __unlazy_fpu(prev_p);
/* Make sure cpu is ready for new context */
if (preload_fpu)
--
1.7.1
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