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authorVineet Gupta <Vineet.Gupta1@synopsys.com>2014-04-30 15:26:45 +0530
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-05-13 13:59:46 +0200
commit149849f8b5e2b6f3424dde4ad95c521954bafeb9 (patch)
treef146beafe1e1cdc94808e03f486600aa879cca69
parentec2d1018b19afeedaba7e0aff6ccd0f0c73c00e4 (diff)
ARC: !PREEMPT: Ensure Return to kernel mode is IRQ safe
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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--arch/arc/kernel/entry.S8
1 files changed, 5 insertions, 3 deletions
diff --git a/arch/arc/kernel/entry.S b/arch/arc/kernel/entry.S
index 57f38333834b..6f3cd0fb4b54 100644
--- 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]