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arm64: remove irq_count and do_softirq_own_stack()

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sysrq_handle_reboot() re-enables interrupts while on the irq stack. The
irq_stack implementation wrongly assumed this would only ever happen
via the softirq path, allowing it to update irq_count late, in
do_softirq_own_stack().

This means if an irq occurs in sysrq_handle_reboot(), during
emergency_restart() the stack will be corrupted, as irq_count wasn't
updated.

Lose the optimisation, and instead of moving the adding/subtracting of
irq_count into irq_stack_entry/irq_stack_exit, remove it, and compare
sp_el0 (struct thread_info) with sp & ~(THREAD_SIZE - 1). This tells us
if we are on a task stack, if so, we can safely switch to the irq stack.
Finally, remove do_softirq_own_stack(), we don't need it anymore.

Reported-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>
[will: use get_thread_info macro]
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
James Morse
2015-12-18 16:01:47 +00:00
committed by Will Deacon
parent 66b3923a1a
commit d224a69e3d
3 changed files with 11 additions and 48 deletions
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19
arch/arm64/kernel/entry.S
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@@ -181,19 +181,20 @@ alternative_endif
.macro irq_stack_entry
mov x19, sp // preserve the original sp
this_cpu_ptr irq_stack, x25, x26
/*
* Check the lowest address on irq_stack for the irq_count value,
* incremented by do_softirq_own_stack if we have re-enabled irqs
* while on the irq_stack.
* Compare sp with the current thread_info, if the top
* ~(THREAD_SIZE - 1) bits match, we are on a task stack, and
* should switch to the irq stack.
*/
ldr x26, [x25]
cbnz x26, 9998f // recursive use?
and x25, x19, #~(THREAD_SIZE - 1)
cmp x25, tsk
b.ne 9998f
/* switch to the irq stack */
this_cpu_ptr irq_stack, x25, x26
mov x26, #IRQ_STACK_START_SP
add x26, x25, x26
/* switch to the irq stack */
mov sp, x26
/*
@@ -405,10 +406,10 @@ el1_irq:
bl trace_hardirqs_off
#endif
get_thread_info tsk
irq_handler
#ifdef CONFIG_PREEMPT
get_thread_info tsk
ldr w24, [tsk, #TI_PREEMPT] // get preempt count
cbnz w24, 1f // preempt count != 0
ldr x0, [tsk, #TI_FLAGS] // get flags