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From: Sergey Vlasov <vsu@altlinux.ru>
To: Alexander Nyberg <alexn@telia.com>
Cc: Rik van Riel <riel@redhat.com>,
	linux-kernel@vger.kernel.org, stian@nixia.no
Subject: Re: timer + fpu stuff locks up computer
Date: Sat, 12 Jun 2004 19:14:22 +0400	[thread overview]
Message-ID: <20040612151422.GC3396@sirius.home> (raw)
In-Reply-To: <1087050351.707.5.camel@boxen>

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On Sat, Jun 12, 2004 at 04:25:51PM +0200, Alexander Nyberg wrote:
> > --- linux-2.6.6/include/asm-i386/i387.h.fp-lockup	2004-05-10 06:33:06 +0400
> > +++ linux-2.6.6/include/asm-i386/i387.h	2004-06-12 17:25:56 +0400
> > @@ -51,7 +51,6 @@
> >  #define __clear_fpu( tsk )					\
> >  do {								\
> >  	if ((tsk)->thread_info->status & TS_USEDFPU) {		\
> > -		asm volatile("fwait");				\
> >  		(tsk)->thread_info->status &= ~TS_USEDFPU;	\
> >  		stts();						\
> >  	}							\
> 
> Sorry for this extremely informative mail but, doesn't work.
> 
> Looks like the problem is only being delayed:
> 
> Pid: 431, comm:                 sshd
> EIP: 0060:[<c0119f98>] CPU: 0
> EIP is at force_sig_info+0x48/0x80
>  EFLAGS: 00000286    Not tainted  (2.6.7-rc3-mm1)
> EAX: 00000000 EBX: de96d7d0 ECX: 00000007 EDX: 00000008
> ESI: 00000008 EDI: 00000286 EBP: de9e3dd4 DS: 007b ES: 007b
> CR0: 8005003b CR2: 080b2664 CR3: 1f48f000 CR4: 000002d0
>  [<c0105560>] do_coprocessor_error+0x0/0x20
>  [<c01054f2>] math_error+0xb2/0x120
>  [<c01d2bb8>] fast_clear_page+0x8/0x50
...

Grrr.  I was testing on a fairly generic kernel configuration which
did not include fast_clear_page()...

If the FPU state belong to the userspace process, kernel_fpu_begin()
is safe even if some exceptions are pending.  However, after
__clear_fpu() the FPU is "orphaned", and kernel_fpu_begin() does
nothing with it.

Replacing fwait with fnclex instead of removing it completely should
avoid the fault later.  However, looks like we really need the proper
fix - teach do_coprocessor_error() to recognize kernel mode faults and
fixup them.

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  parent reply	other threads:[~2004-06-12 15:14 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2004-06-09 21:02 timer + fpu stuff locks my console race stian
2004-06-10 21:00 ` Matias Hermanrud Fjeld
2004-06-11  6:08   ` Lars Age Kamfjord
2004-06-12  2:53 ` Rik van Riel
2004-06-12  3:50   ` Rik van Riel
2004-06-12 13:44     ` Sergey Vlasov
2004-06-12 13:57       ` stian
2004-06-12 14:28         ` Sergey Vlasov
2004-06-12 14:25       ` timer + fpu stuff locks up computer Alexander Nyberg
2004-06-12 14:42         ` stian
2004-06-12 15:20           ` martin capitanio
2004-06-12 16:15             ` stian
2004-06-12 15:14         ` Sergey Vlasov [this message]
2004-06-12 18:45           ` Sergey Vlasov
2004-06-12 20:27             ` Alexander Nyberg
2004-06-12  4:35   ` timer + fpu stuff locks my console race Matt Mackall
     [not found] <26h3z-t3-15@gated-at.bofh.it>
     [not found] ` <26hGq-Zr-29@gated-at.bofh.it>
     [not found]   ` <26isF-1Im-11@gated-at.bofh.it>
     [not found]     ` <26lJU-4lC-23@gated-at.bofh.it>
2004-06-12 22:08       ` timer + fpu stuff locks up computer Andi Kleen
2004-06-13 13:06         ` Sergey Vlasov

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