From: Vineet Gupta Date: Wed, 30 Apr 2014 09:56:45 +0000 (+0530) Subject: ARC: !PREEMPT: Ensure Return to kernel mode is IRQ safe X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=8aa9e85adac609588eeec356e5a85059b3b819ba;p=GitHub%2FLineageOS%2FG12%2Fandroid_kernel_amlogic_linux-4.9.git ARC: !PREEMPT: Ensure Return to kernel mode is IRQ safe 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 Cc: #3.10, 3.12, 3.13, 3.14 Cc: Anton Kolesov Cc: Francois Bedard Signed-off-by: Linus Torvalds --- diff --git a/arch/arc/kernel/entry.S b/arch/arc/kernel/entry.S index 819dd5f7eb05..29b82adbf0b4 100644 --- a/arch/arc/kernel/entry.S +++ b/arch/arc/kernel/entry.S @@ -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]