svn commit: r308101 - head/sys/dev/hwpmc

[Andriy Gapon]

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);
 }