Date: Sun, 30 Oct 2016 09:38:10 +0000 (UTC) From: Andriy Gapon <avg@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r308101 - head/sys/dev/hwpmc Message-ID: <201610300938.u9U9cAvu064810@repo.freebsd.org>
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Author: avg Date: Sun Oct 30 09:38:10 2016 New Revision: 308101 URL: https://svnweb.freebsd.org/changeset/base/308101 Log: hwpmc: fix a race between amd_stop_pmc and amd_intr It is possible that wrmsr in amd_stop_pmc() causes an overflow in a counter that it disables. In that case a non-maskable interrupt is generated. The interrupt handler code was written in such a way that it would re-enable the counter. That would lead to an unexpected interrupt later on. This problem was easy to reproduce with $ pmcstat -T -P instructions -t $pid if the target process is sufficiently busy and there are context switches from time to time. There would be a lot of interrupts to "race" with amd_stop_pmc() called during the context switches. The problem affected only AMD processors. While there, trace whether amd_intr() claimed an interrupt. Reviewed by: jhb MFC after: 2 weeks Modified: head/sys/dev/hwpmc/hwpmc_amd.c Modified: head/sys/dev/hwpmc/hwpmc_amd.c ============================================================================== --- head/sys/dev/hwpmc/hwpmc_amd.c Sun Oct 30 02:57:47 2016 (r308100) +++ head/sys/dev/hwpmc/hwpmc_amd.c Sun Oct 30 09:38:10 2016 (r308101) @@ -689,12 +689,13 @@ amd_intr(int cpu, struct trapframe *tf) error = pmc_process_interrupt(cpu, PMC_HR, pm, tf, TRAPF_USERMODE(tf)); if (error == 0) - wrmsr(evsel, config | AMD_PMC_ENABLE); + wrmsr(evsel, config); } atomic_add_int(retval ? &pmc_stats.pm_intr_processed : &pmc_stats.pm_intr_ignored, 1); + PMCDBG1(MDP,INT,2, "retval=%d", retval); return (retval); }
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