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runtime: fix crash during cpu profiling

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mp->mcache can be concurrently modified by runtime·helpgc.
In such case sigprof can remember mcache=nil, then helpgc sets it to non-nil,
then sigprof restores it back to nil, GC crashes with nil mcache.

R=rsc
CC=golang-codereviews
https://golang.org/cl/58860044
This commit is contained in:
Dmitriy Vyukov 2014-02-10 20:24:47 +04:00
parent e56e4e0193
commit 373e1e94d8
1 changed files with 3 additions and 5 deletions
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8
src/pkg/runtime/proc.c
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@ -2115,7 +2115,6 @@ runtime·sigprof(uint8 *pc, uint8 *sp, uint8 *lr, G *gp, M *mp)
{ {
int32 n; int32 n;
bool traceback; bool traceback;
MCache *mcache;
// Do not use global m in this function, use mp instead. // Do not use global m in this function, use mp instead.
// On windows one m is sending reports about all the g's, so m means a wrong thing. // On windows one m is sending reports about all the g's, so m means a wrong thing.
byte m; byte m;
@ -2127,8 +2126,7 @@ runtime·sigprof(uint8 *pc, uint8 *sp, uint8 *lr, G *gp, M *mp)
return; return;
// Profiling runs concurrently with GC, so it must not allocate. // Profiling runs concurrently with GC, so it must not allocate.
mcache = mp->mcache; mp->mallocing++;
mp->mcache = nil;
// Define that a "user g" is a user-created goroutine, and a "system g" // Define that a "user g" is a user-created goroutine, and a "system g"
// is one that is m->g0 or m->gsignal. We've only made sure that we // is one that is m->g0 or m->gsignal. We've only made sure that we
@ -2216,7 +2214,7 @@ runtime·sigprof(uint8 *pc, uint8 *sp, uint8 *lr, G *gp, M *mp)
runtime·lock(&prof); runtime·lock(&prof);
if(prof.fn == nil) { if(prof.fn == nil) {
runtime·unlock(&prof); runtime·unlock(&prof);
mp->mcache = mcache; mp->mallocing--;
return; return;
} }
n = 0; n = 0;
@ -2229,7 +2227,7 @@ runtime·sigprof(uint8 *pc, uint8 *sp, uint8 *lr, G *gp, M *mp)
} }
prof.fn(prof.pcbuf, n); prof.fn(prof.pcbuf, n);
runtime·unlock(&prof); runtime·unlock(&prof);
mp->mcache = mcache; mp->mallocing--;
} }
// Arrange to call fn with a traceback hz times a second. // Arrange to call fn with a traceback hz times a second.