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| author |   Will Deacon <will.deacon@arm.com> | 2015-12-09 13:58:42 +0000 |
|---|---|---|
| committer | Will Deacon <will.deacon@arm.com> | 2015-12-09 13:59:09 +0000 |
| commit | 7596abf2e5661d52c4f414f37addeed54e098880 (patch) | |
| tree | 82ce4a4d4fe186bdf0a487f6f0def4ec6e1c18fe /arch/arm64/kernel | |
| parent | arm64: Add do_softirq_own_stack() and enable irq_stacks (diff) | |
| download | linux-dev-7596abf2e5661d52c4f414f37addeed54e098880.tar.xz linux-dev-7596abf2e5661d52c4f414f37addeed54e098880.zip | |
arm64: irq: fix walking from irq stack to task stack
Running with CONFIG_DEBUG_SPINLOCK=y can trigger a BUG with the new IRQ
stack code:
BUG: spinlock lockup suspected on CPU#1
This is due to the IRQ_STACK_TO_TASK_STACK macro incorrectly retrieving
the task stack pointer stashed at the top of the IRQ stack.
Sayeth James:
| Yup, this is what is happening. Its an off-by-one due to broken
| thinking about how the stack works. My broken thinking was:
|
| > top ------------
| > | dummy_lr | <- irq_stack_ptr
| > ------------
| > | x29 |
| > ------------
| > | x19 | <- irq_stack_ptr - 0x10
| > ------------
| > | xzr |
| > ------------
|
| But the stack-pointer is decreased before use. So it actually looks
| like this:
|
| > ------------
| > | | <- irq_stack_ptr
| > top ------------
| > | dummy_lr |
| > ------------
| > | x29 | <- irq_stack_ptr - 0x10
| > ------------
| > | x19 |
| > ------------
| > | xzr | <- irq_stack_ptr - 0x20
| > ------------
|
| The value being used as the original stack is x29, which in all the
| tests is sp but without the current frames data, hence there are no
| missing frames in the output.
|
| Jungseok Lee picked it up with a 32bit user space because aarch32
| can't use x29, so it remains 0 forever. The fix he posted is correct.
This patch fixes the macro and adds some of this wisdom to a comment,
so that the layout of the IRQ stack is well understood.
Cc: James Morse <james.morse@arm.com>
Reported-by: Jungseok Lee <jungseoklee85@gmail.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Diffstat (limited to 'arch/arm64/kernel')
| -rw-r--r-- | arch/arm64/kernel/entry.S | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index 8f7e737949fe..be7ec544b540 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -199,7 +199,7 @@ alternative_endif /* Add a dummy stack frame */ stp x29, \dummy_lr, [sp, #-16]! // dummy stack frame mov x29, sp - stp xzr, x19, [sp, #-16]! + stp x19, xzr, [sp, #-16]! 9998: .endm |