linux-kernel - PATCH -RCU locking on last_VFP_context[cpu] in vfp

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Date:	Mon, 11 Aug 2014 15:24:18 -0700
From:	Sadasivan Shaiju <sshaiju@...sta.com>
To:	linux@....linux.org.uk
Cc:	linux-kernel@...r.kernel.org
Subject: PATCH -RCU locking on last_VFP_context[cpu] in vfp_notifier [2.6.32]

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@...sta.com
(shaiju_sada@...oo.com)

Regards,
Shaiju.
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