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>
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@ -229,6 +229,8 @@ static void set_mtrr(unsigned int reg, unsigned long base,
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data.smp_size = size;
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data.smp_size = size;
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data.smp_type = type;
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data.smp_type = type;
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atomic_set(&data.count, num_booting_cpus() - 1);
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atomic_set(&data.count, num_booting_cpus() - 1);
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/* make sure data.count is visible before unleashing other CPUs */
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smp_wmb();
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atomic_set(&data.gate,0);
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atomic_set(&data.gate,0);
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/* Start the ball rolling on other CPUs */
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/* Start the ball rolling on other CPUs */
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@ -242,6 +244,7 @@ static void set_mtrr(unsigned int reg, unsigned long base,
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/* ok, reset count and toggle gate */
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/* ok, reset count and toggle gate */
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atomic_set(&data.count, num_booting_cpus() - 1);
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atomic_set(&data.count, num_booting_cpus() - 1);
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smp_wmb();
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atomic_set(&data.gate,1);
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atomic_set(&data.gate,1);
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/* do our MTRR business */
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/* do our MTRR business */
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@ -260,6 +263,7 @@ static void set_mtrr(unsigned int reg, unsigned long base,
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cpu_relax();
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cpu_relax();
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atomic_set(&data.count, num_booting_cpus() - 1);
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atomic_set(&data.count, num_booting_cpus() - 1);
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smp_wmb();
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atomic_set(&data.gate,0);
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atomic_set(&data.gate,0);
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/*
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/*
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