This is a note to let you know that I've just added the patch titled
ARC: !PREEMPT: Ensure Return to kernel mode is IRQ safe
to the 3.10-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
arc-preempt-ensure-return-to-kernel-mode-is-irq-safe.patch
and it can be found in the queue-3.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 8aa9e85adac609588eeec356e5a85059b3b819ba Mon Sep 17 00:00:00 2001
From: Vineet Gupta <Vineet.Gupta1@xxxxxxxxxxxx>
Date: Wed, 30 Apr 2014 15:26:45 +0530
Subject: ARC: !PREEMPT: Ensure Return to kernel mode is IRQ safe
From: Vineet Gupta <Vineet.Gupta1@xxxxxxxxxxxx>
commit 8aa9e85adac609588eeec356e5a85059b3b819ba upstream.
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@xxxxxxxxxxxx>
Cc: Anton Kolesov <Anton.Kolesov@xxxxxxxxxxxx>
Cc: Francois Bedard <Francois.Bedard@xxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/arc/kernel/entry.S | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
--- a/arch/arc/kernel/entry.S
+++ b/arch/arc/kernel/entry.S
@@ -651,11 +651,13 @@ 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]
Patches currently in stable-queue which might be from Vineet.Gupta1@xxxxxxxxxxxx are
queue-3.10/arc-preempt-ensure-return-to-kernel-mode-is-irq-safe.patch
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