Commit d224a69e authored by James Morse's avatar James Morse Committed by Will Deacon
Browse files

arm64: remove irq_count and do_softirq_own_stack() 



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: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarJames Morse <james.morse@arm.com>
[will: use get_thread_info macro]
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent 66b3923a

arch/arm64/include/asm/irq.h

+0 −2
Original line number Diff line number Diff line
@@ -11,8 +11,6 @@ 
#include <asm-generic/irq.h>

#include <asm/thread_info.h>



#define __ARCH_HAS_DO_SOFTIRQ



struct pt_regs;



DECLARE_PER_CPU(unsigned long [IRQ_STACK_SIZE/sizeof(long)], irq_stack);

arch/arm64/kernel/entry.S

+10 −9
Original line number Diff line number Diff line
@@ -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

arch/arm64/kernel/irq.c

+1 −37
Original line number Diff line number Diff line
@@ -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();

	}

}

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