Messages in this thread Patch in this message | | | Date | Fri, 12 Jun 2015 16:35:25 -0300 | From | Arnaldo Carvalho de Melo <> | Subject | Re: [PATCH] perf, tools: Fix crash in 'perf trace' |
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Em Thu, Jun 11, 2015 at 11:00:04PM -0700, Sukadev Bhattiprolu escreveu: > >From 6669ed960a3ee4f9a02790f60b6a73ffc82fd6de Mon Sep 17 00:00:00 2001 > From: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com> > Date: Fri, 12 Jun 2015 01:28:36 -0400 > Subject: [PATCH] perf, tools: Fix crash in perf trace > > I get following crash on multiple systems and across several releases > (at least since v3.18).
Trying it in perf/core I get:
util/evlist.c: In function ‘perf_evlist__mmap_read’: util/evlist.c:645:6: error: wrong type argument to unary exclamation mark if (!md->refcnt)
Trying after changing it to !atomic_read(&md->refcnt)
And it fixes the segfault that I reproduced, but this still looks strange, i.e. if it hit zero, then it should not have been used at this point anymore... Will look at it again in the weekend. :-\
- Arnaldo
> Core was generated by `/tmp/perf trace sleep 0.2 '. > Program terminated with signal SIGSEGV, Segmentation fault. > #0 perf_mmap__read_head (mm=0x3fff9bf30070) at util/evlist.h:195 > 195 u64 head = ACCESS_ONCE(pc->data_head); > (gdb) bt > #0 perf_mmap__read_head (mm=0x3fff9bf30070) at util/evlist.h:195 > #1 perf_evlist__mmap_read (evlist=0x10027f11910, idx=<optimized out>) > at util/evlist.c:637 > #2 0x000000001003ce4c in trace__run (argv=<optimized out>, > argc=<optimized out>, trace=0x3fffd7b28288) at builtin-trace.c:2259 > #3 cmd_trace (argc=<optimized out>, argv=<optimized out>, > prefix=<optimized out>) at builtin-trace.c:2799 > #4 0x00000000100657b8 in run_builtin (p=0x10176798 <commands+480>, argc=3, > argv=0x3fffd7b2b550) at perf.c:370 > #5 0x00000000100063e8 in handle_internal_command (argv=0x3fffd7b2b550, argc=3) > at perf.c:429 > #6 run_argv (argv=0x3fffd7b2af70, argcp=0x3fffd7b2af7c) at perf.c:473 > #7 main (argc=3, argv=0x3fffd7b2b550) at perf.c:588 > > The problem seems to be a race condition, when the application has just > exited. Some/all fds associated with the perf-events (tracepoints) go > into a POLLHUP/ POLLERR state and the mmap region associated with those > events are unmapped (in perf_evlist__filter_pollfd()). > > But we go back and do a perf_evlist__mmap_read() which assumes that the > mmaps are still valid and we hit the crash. > > If the mapping for an event is released, its refcnt is 0 (and ->base > is NULL), so ensure we have non-zero refcount before accessing the map. > > Note that perf-record has a similar logic but unlike perf-trace, the > record__mmap_read_all() checks the evlist->mmap[i].base before accessing > the map. > > Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com> > --- > tools/perf/util/evlist.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c > index 080be93..084535b 100644 > --- a/tools/perf/util/evlist.c > +++ b/tools/perf/util/evlist.c > @@ -634,11 +634,18 @@ static struct perf_evsel *perf_evlist__event2evsel(struct perf_evlist *evlist, > union perf_event *perf_evlist__mmap_read(struct perf_evlist *evlist, int idx) > { > struct perf_mmap *md = &evlist->mmap[idx]; > - u64 head = perf_mmap__read_head(md); > + u64 head; > u64 old = md->prev; > unsigned char *data = md->base + page_size; > union perf_event *event = NULL; > > + /* > + * Check if event was unmapped due to a POLLHUP/POLLERR. > + */ > + if (!md->refcnt) > + return NULL; > + > + head = perf_mmap__read_head(md); > if (evlist->overwrite) { > /* > * If we're further behind than half the buffer, there's a chance > -- > 2.1.4
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