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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: Loic Prylli <loic@myri.com>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Loic Prylli 2007-07-06 02:39:52 -07:00 committed by Linus Torvalds
parent 1e2e99f0e4
commit d25c1ba2fa
1 changed files with 4 additions and 0 deletions
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4
arch/i386/kernel/cpu/mtrr/main.c
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@ -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);
/*