Commit-ID: 184e1fdfea066ab8f12a1e8912f402d2d6556d11 Gitweb: http://git.kernel.org/tip/184e1fdfea066ab8f12a1e8912f402d2d6556d11 Author: Huang Ying <ying.huang@xxxxxxxxx> AuthorDate: Mon, 15 Jun 2009 15:37:07 +0800 Committer: H. Peter Anvin <hpa@xxxxxxxxx> CommitDate: Tue, 16 Jun 2009 16:56:04 -0700 x86, mce: fix a race condition about mce_callin and no_way_out If one CPU has no_way_out == 1, all other CPUs should have no_way_out == 1. But despite global_nwo is read after mce_callin, global_nwo is updated after mce_callin too. So it is possible that some CPU read global_nwo before some other CPU update global_nwo, so that no_way_out == 1 for some CPU, while no_way_out == 0 for some other CPU. This patch fixes this race condition via moving mce_callin updating after global_nwo updating, with a smp_wmb in between. A smp_rmb is added between their reading too. Signed-off-by: Huang Ying <ying.huang@xxxxxxxxx> Acked-by: Andi Kleen <ak@xxxxxxxxxxxxxxx> Acked-by: Hidetoshi Seto <seto.hidetoshi@xxxxxxxxxxxxxx> --- arch/x86/kernel/cpu/mcheck/mce.c | 12 ++++++++++-- 1 files changed, 10 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c index fabba15..19294b8 100644 --- a/arch/x86/kernel/cpu/mcheck/mce.c +++ b/arch/x86/kernel/cpu/mcheck/mce.c @@ -703,6 +703,11 @@ static int mce_start(int no_way_out, int *order) } atomic_add(no_way_out, &global_nwo); + /* + * global_nwo should be updated before mce_callin + */ + smp_wmb(); + *order = atomic_add_return(1, &mce_callin); /* * Wait for everyone. @@ -717,6 +722,10 @@ static int mce_start(int no_way_out, int *order) } /* + * mce_callin should be read before global_nwo + */ + smp_rmb(); + /* * Cache the global no_way_out state. */ nwo = atomic_read(&global_nwo); @@ -862,7 +871,7 @@ void do_machine_check(struct pt_regs *regs, long error_code) * Establish sequential order between the CPUs entering the machine * check handler. */ - int order; + int order = -1; /* * If no_way_out gets set, there is no safe way to recover from this @@ -887,7 +896,6 @@ void do_machine_check(struct pt_regs *regs, long error_code) if (!banks) goto out; - order = atomic_add_return(1, &mce_callin); mce_setup(&m); m.mcgstatus = mce_rdmsrl(MSR_IA32_MCG_STATUS); -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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