[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: Andi Kleen <ak@suse.de>
diff --git a/arch/x86_64/kernel/process.c b/arch/x86_64/kernel/process.c
index 49f7fac..f622605 100644
--- a/arch/x86_64/kernel/process.c
+++ b/arch/x86_64/kernel/process.c
@@ -88,9 +88,8 @@
static void __exit_idle(void)
{
- if (read_pda(isidle) == 0)
+ if (test_and_clear_bit_pda(0, isidle) == 0)
return;
- write_pda(isidle, 0);
atomic_notifier_call_chain(&idle_notifier, IDLE_END, NULL);
}
diff --git a/include/asm-x86_64/pda.h b/include/asm-x86_64/pda.h
index 14996d9..5642634 100644
--- a/include/asm-x86_64/pda.h
+++ b/include/asm-x86_64/pda.h
@@ -109,6 +109,15 @@
#define sub_pda(field,val) pda_to_op("sub",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
#define PDA_STACKOFFSET (5*8)