Messages in this thread Patch in this message | | | From | Luis Henriques <> | Subject | [PATCH 3.11 65/70] ARC: !PREEMPT: Ensure Return to kernel mode is IRQ safe | Date | Wed, 7 May 2014 14:13:08 +0100 |
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3.11.10.10 -stable review patch. If anyone has any objections, please let me know.
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From: Vineet Gupta <Vineet.Gupta1@synopsys.com>
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@synopsys.com> Cc: Anton Kolesov <Anton.Kolesov@synopsys.com> Cc: Francois Bedard <Francois.Bedard@synopsys.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- arch/arc/kernel/entry.S | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/arch/arc/kernel/entry.S b/arch/arc/kernel/entry.S index 89f7961..ca6e48b 100644 --- a/arch/arc/kernel/entry.S +++ b/arch/arc/kernel/entry.S @@ -640,11 +640,13 @@ 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] -- 1.9.1
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