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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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38
arch/arm64/kernel/irq.c
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@@ -25,24 +25,14 @@
#include <linux/irq.h>
#include <linux/smp.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/irqchip.h>
#include <linux/seq_file.h>
unsigned long irq_err_count;
/*
* irq stack only needs to be 16 byte aligned - not IRQ_STACK_SIZE aligned.
* irq_stack[0] is used as irq_count, a non-zero value indicates the stack
* is in use, and el?_irq() shouldn't switch to it. This is used to detect
* recursive use of the irq_stack, it is lazily updated by
* do_softirq_own_stack(), which is called on the irq_stack, before
* re-enabling interrupts to process softirqs.
*/
/* irq stack only needs to be 16 byte aligned - not IRQ_STACK_SIZE aligned. */
DEFINE_PER_CPU(unsigned long [IRQ_STACK_SIZE/sizeof(long)], irq_stack) __aligned(16);
#define IRQ_COUNT() (*per_cpu(irq_stack, smp_processor_id()))
int arch_show_interrupts(struct seq_file *p, int prec)
{
show_ipi_list(p, prec);
@@ -66,29 +56,3 @@ void __init init_IRQ(void)
if (!handle_arch_irq)
panic("No interrupt controller found.");
}
/*
* do_softirq_own_stack() is called from irq_exit() before __do_softirq()
* re-enables interrupts, at which point we may re-enter el?_irq(). We
* increase irq_count here so that el1_irq() knows that it is already on the
* irq stack.
*
* Called with interrupts disabled, so we don't worry about moving cpu, or
* being interrupted while modifying irq_count.
*
* This function doesn't actually switch stack.
*/
void do_softirq_own_stack(void)
{
int cpu = smp_processor_id();
WARN_ON_ONCE(!irqs_disabled());
if (on_irq_stack(current_stack_pointer, cpu)) {
IRQ_COUNT()++;
__do_softirq();
IRQ_COUNT()--;
} else {
__do_softirq();
}
}