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Commit d25c1ba2 authored by Loic Prylli's avatar Loic Prylli Committed by Linus Torvalds
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MTRR: Fix race causing set_mtrr to go into infinite loop 



Processors synchronization in set_mtrr requires the .gate field to be set
after .count field is properly initialized.  Without an explicit barrier,
the compiler was reordering those memory stores.  That was sometimes
causing a processor (in ipi_handler) to see the .gate change and decrement
.count before the latter is set by set_mtrr() (which then hangs in a
infinite loop with irqs disabled).

Signed-off-by: default avatarLoic Prylli <loic@myri.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 1e2e99f0

arch/i386/kernel/cpu/mtrr/main.c

+4 −0
Original line number Diff line number Diff line
@@ -229,6 +229,8 @@ static void set_mtrr(unsigned int reg, unsigned long base, 
	data.smp_size = size;

	data.smp_type = type;

	atomic_set(&data.count, num_booting_cpus() - 1);

	/* make sure data.count is visible before unleashing other CPUs */

	smp_wmb();

	atomic_set(&data.gate,0);



	/*  Start the ball rolling on other CPUs  */
@@ -242,6 +244,7 @@ static void set_mtrr(unsigned int reg, unsigned long base, 


	/* ok, reset count and toggle gate */

	atomic_set(&data.count, num_booting_cpus() - 1);

	smp_wmb();

	atomic_set(&data.gate,1);



	/* do our MTRR business */
@@ -260,6 +263,7 @@ static void set_mtrr(unsigned int reg, unsigned long base, 
		cpu_relax();



	atomic_set(&data.count, num_booting_cpus() - 1);

	smp_wmb();

	atomic_set(&data.gate,0);



	/*