From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: Sadasivan Shaiju <sshaiju@mvista.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: PATCH -RCU locking on last_VFP_context[cpu] in vfp_notifier [2.6.32]
Date: Mon, 11 Aug 2014 23:49:25 +0100 [thread overview]
Message-ID: <20140811224925.GE30401@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <ad46c9518e35397c8f4d281a3f88d129@mail.gmail.com>
On Mon, Aug 11, 2014 at 03:24:18PM -0700, Sadasivan Shaiju wrote:
> Hi ,
>
> I work for Montavista (Cavium Inc) as a Technical Lead . I want to
> push some of the kernel patches to rt community (2.6.32 kernel 2.6.33
> rt patch) , so that It will go to the main line These patches are
> reviewed and approved by our system Architect. I request you to
> include in the main line . These issues were reported during econa
> board bringup at montavista.
>
> Problem Description:
> Using cge60-econa-cns3420-2.6.32, the kernel failed to boot with the
> following
> error:
>
> Internal error: Oops: 817 [#1] from cpu 1 PREEMPT SMP
> last sysfs file: /sys/devices/virtual/bdi/0:19/uevent
> Modules linked in: hmac ctr deflate
> CPU: 1 Tainted: G W (2.6.32.46.cge #1)
> PC is at vfp_notifier+0x48/0xbc
> LR is at vfp_notifier+0x44/0xbc
> pc : [] lr : [] psr: 60000013
> sp : aeee1d30 ip : aeee1d50 fp : aeee1d4c
> r10: af8d6460 r9 : ffffffff r8 : af88c000
> r7 : a05ba584 r6 : af88c000 r5 : 00000001 r4 : 40000000
> r3 : 00000000 r2 : 00000000 r1 : 40000000 r0 : aeee0230
> Flags: nZCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user
> Control: 00c5787d Table: 2eeec00a DAC: 00000017
> Process grep (pid: 1710, stack limit = 0xaeee0270)
> Stack: from cpu 1 (0xaeee1d30 to 0xaeee2000)
>
> Root Cause:
> On the SMP architecture, last_VFP_context[cpu] becomes NULL because it
> gets
> released on a different CPU.
>
> How Solved:
> Fixed by exiting the thread instead of releasing the thread in the
> vfp_notifier.
>
> I request you to include the above patch to the main line kernel . If
> any questions please contact me at sshaiju@mvista.com
> (shaiju_sada@yahoo.com)
This is totally insufficient for fixing a bug in a complex piece of code.
You fail to explain exactly _how_ the bug arises. You say
"last_VFP_context[cpu] becomes NULL because it gets released on a
different CPU" - how does that happen?
The only places that last_VFP_context[cpu] is set to NULL is within a
cpu = get_cpu()..put_cpu() region, which by definition *must* be running
on the CPU specified by 'cpu'.
Without a proper diagnosis showing exactly what the race is which causes
the above oops, there's nothing I can do. Sorry.
--
FTTC broadband for 0.8mile line: currently at 9.5Mbps down 400kbps up
according to speedtest.net.
next prev parent reply other threads:[~2014-08-11 22:49 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-11 22:24 PATCH -RCU locking on last_VFP_context[cpu] in vfp_notifier [2.6.32] Sadasivan Shaiju
2014-08-11 22:49 ` Russell King - ARM Linux [this message]
2014-08-12 1:12 ` Sadasivan Shaiju
2014-08-12 9:26 ` Russell King - ARM Linux
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