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Commit ef2b343e authored by Hugh Dickins's avatar Hugh Dickins Committed by Paul Mackerras
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[POWERPC] Make soft_enabled irqs preempt safe 



Rewrite local_get_flags and local_irq_disable to use r13 explicitly,
to avoid the risk that gcc will split get_paca()->soft_enabled into a
sequence unsafe against preemption.  Similar care in local_irq_restore.

Signed-off-by: default avatarHugh Dickins <hugh@veritas.com>
Signed-off-by: default avatarPaul Mackerras <paulus@samba.org>
parent 56291e19

arch/powerpc/kernel/irq.c

+52 −5
Original line number Diff line number Diff line
@@ -97,22 +97,69 @@ EXPORT_SYMBOL(irq_desc); 


int distribute_irqs = 1;



static inline unsigned long get_hard_enabled(void)

{

	unsigned long enabled;



	__asm__ __volatile__("lbz %0,%1(13)"

	: "=r" (enabled) : "i" (offsetof(struct paca_struct, hard_enabled)));



	return enabled;

}



static inline void set_soft_enabled(unsigned long enable)

{

	__asm__ __volatile__("stb %0,%1(13)"

	: : "r" (enable), "i" (offsetof(struct paca_struct, soft_enabled)));

}



void local_irq_restore(unsigned long en)

{

	get_paca()->soft_enabled = en;

	/*

	 * get_paca()->soft_enabled = en;

	 * Is it ever valid to use local_irq_restore(0) when soft_enabled is 1?

	 * That was allowed before, and in such a case we do need to take care

	 * that gcc will set soft_enabled directly via r13, not choose to use

	 * an intermediate register, lest we're preempted to a different cpu.

	 */

	set_soft_enabled(en);

	if (!en)

		return;



	if (firmware_has_feature(FW_FEATURE_ISERIES)) {

		if (get_paca()->lppaca_ptr->int_dword.any_int)

		/*

		 * Do we need to disable preemption here?  Not really: in the

		 * unlikely event that we're preempted to a different cpu in

		 * between getting r13, loading its lppaca_ptr, and loading

		 * its any_int, we might call iseries_handle_interrupts without

		 * an interrupt pending on the new cpu, but that's no disaster,

		 * is it?  And the business of preempting us off the old cpu

		 * would itself involve a local_irq_restore which handles the

		 * interrupt to that cpu.

		 *

		 * But use "local_paca->lppaca_ptr" instead of "get_lppaca()"

		 * to avoid any preemption checking added into get_paca().

		 */

		if (local_paca->lppaca_ptr->int_dword.any_int)

			iseries_handle_interrupts();

		return;

	}



	if (get_paca()->hard_enabled)

	/*

	 * if (get_paca()->hard_enabled) return;

	 * But again we need to take care that gcc gets hard_enabled directly

	 * via r13, not choose to use an intermediate register, lest we're

	 * preempted to a different cpu in between the two instructions.

	 */

	if (get_hard_enabled())

		return;

	/* need to hard-enable interrupts here */

	get_paca()->hard_enabled = en;



	/*

	 * Need to hard-enable interrupts here.  Since currently disabled,

	 * no need to take further asm precautions against preemption; but

	 * use local_paca instead of get_paca() to avoid preemption checking.

	 */

	local_paca->hard_enabled = en;

	if ((int)mfspr(SPRN_DEC) < 0)

		mtspr(SPRN_DEC, 1);

	hard_irq_enable();

include/asm-powerpc/hw_irq.h

+15 −5
Original line number Diff line number Diff line
@@ -18,15 +18,25 @@ extern void timer_interrupt(struct pt_regs *); 


static inline unsigned long local_get_flags(void)

{

	return get_paca()->soft_enabled;

	unsigned long flags;



	__asm__ __volatile__("lbz %0,%1(13)"

	: "=r" (flags)

	: "i" (offsetof(struct paca_struct, soft_enabled)));



	return flags;

}



static inline unsigned long local_irq_disable(void)

{

	unsigned long flag = get_paca()->soft_enabled;

	get_paca()->soft_enabled = 0;

	barrier();

	return flag;

	unsigned long flags, zero;



	__asm__ __volatile__("li %1,0; lbz %0,%2(13); stb %1,%2(13)"

	: "=r" (flags), "=&r" (zero)

	: "i" (offsetof(struct paca_struct, soft_enabled))

	: "memory");



	return flags;

}



extern void local_irq_restore(unsigned long);