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ARC: !PREEMPT: Ensure Return to kernel mode is IRQ safe

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There was a very small race window where resume to kernel mode from a
Exception Path (or pure kernel mode which is true for most of ARC
exceptions anyways), was not disabling interrupts in restore_regs,
clobbering the exception regs

Anton found the culprit call flow (after many sleepless nights)

| 1. we got a Trap from user land
| 2. started to service it.
| 3. While doing some stuff on user-land memory (I think it is padzero()),
|     we got a DataTlbMiss
| 4. On return from it we are taking "resume_kernel_mode" path
| 5. NEED_RESHED is not set, so we go to "return from exception" path in
|     restore regs.
| 6. there seems to be IRQ happening

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Cc: <stable@vger.kernel.org>   #3.10, 3.12, 3.13, 3.14
Cc: Anton Kolesov <Anton.Kolesov@synopsys.com>
Cc: Francois Bedard <Francois.Bedard@synopsys.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Vineet Gupta 2014-04-30 15:26:45 +05:30 committed by Linus Torvalds
parent 71dc96e39d
commit 8aa9e85ada
1 changed files with 5 additions and 3 deletions
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8
arch/arc/kernel/entry.S
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@ -614,11 +614,13 @@ resume_user_mode_begin:
resume_kernel_mode:
#ifdef CONFIG_PREEMPT
; This is a must for preempt_schedule_irq()
; Disable Interrupts from this point on
; CONFIG_PREEMPT: This is a must for preempt_schedule_irq()
; !CONFIG_PREEMPT: To ensure restore_regs is intr safe
IRQ_DISABLE r9
#ifdef CONFIG_PREEMPT
; Can't preempt if preemption disabled
GET_CURR_THR_INFO_FROM_SP r10
ld r8, [r10, THREAD_INFO_PREEMPT_COUNT]