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Commit 9446868b authored by Andi Kleen's avatar Andi Kleen Committed by Andi Kleen
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[PATCH] x86-64: Fix race in exit_idle 



When another interrupt happens in exit_idle the exit idle notifier
could be called an incorrect number of times.

Add a test_and_clear_bit_pda and use it handle the bit
atomically against interrupts to avoid this.

Pointed out by Stephane Eranian

Signed-off-by: default avatarAndi Kleen <ak@suse.de>
parent 8c131af1

arch/x86_64/kernel/process.c

+1 −2
Original line number Original line Diff line number Diff line
@@ -88,9 +88,8 @@ void enter_idle(void) 




static void __exit_idle(void)

static void __exit_idle(void)

{

{

	if (read_pda(isidle) == 0)

	if (test_and_clear_bit_pda(0, isidle) == 0)

		return;

		return;

	write_pda(isidle, 0);

	atomic_notifier_call_chain(&idle_notifier, IDLE_END, NULL);

	atomic_notifier_call_chain(&idle_notifier, IDLE_END, NULL);

}

}

include/asm-x86_64/pda.h

+9 −0
Original line number Original line Diff line number Diff line
@@ -109,6 +109,15 @@ extern struct x8664_pda _proxy_pda; 
#define sub_pda(field,val) pda_to_op("sub",field,val)

#define sub_pda(field,val) pda_to_op("sub",field,val)

#define or_pda(field,val) pda_to_op("or",field,val)

#define or_pda(field,val) pda_to_op("or",field,val)





/* This is not atomic against other CPUs -- CPU preemption needs to be off */

#define test_and_clear_bit_pda(bit,field) ({		\

	int old__;						\

	asm volatile("btr %2,%%gs:%c3\n\tsbbl %0,%0"		\

	    : "=r" (old__), "+m" (_proxy_pda.field) 		\

	    : "dIr" (bit), "i" (pda_offset(field)) : "memory");	\

	old__;							\

})



#endif

#endif





#define PDA_STACKOFFSET (5*8)

#define PDA_STACKOFFSET (5*8)