| Message ID | 1435331181-27231-1-git-send-email-chris.j.arges@canonical.com |
|---|---|
| State | New |
| Headers | show |
On Fri, Jun 26, 2015 at 10:06:21AM -0500, Chris J Arges wrote: > From: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com> > > BugLink: http://bugs.launchpad.net/bugs/1410673 > > I get following crash on multiple systems and across several releases > (at least since v3.18). > > 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> > Cc: Jiri Olsa <jolsa@redhat.com> > Cc: Li Zhang <zhlcindy@linux.vnet.ibm.com> > Link: http://lkml.kernel.org/r/20150612060003.GA19913@us.ibm.com > [ Fixed it up to use atomic_read() ] > Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com> > > (backported from commit 7951722da2963cc1f1a7831a37aa2311ac927056) > Signed-off-by: Chris J Arges <chris.j.arges@canonical.com> > > Conflicts: > tools/perf/util/evlist.c > --- > 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 2e507b5..5460e65 100644 > --- a/tools/perf/util/evlist.c > +++ b/tools/perf/util/evlist.c > @@ -635,11 +635,18 @@ 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]; > - unsigned int head = perf_mmap__read_head(md); > + unsigned int head; > unsigned int 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 (!atomic_read(&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 > -- > 1.9.1 > > > -- > kernel-team mailing list > kernel-team@lists.ubuntu.com > https://lists.ubuntu.com/mailman/listinfo/kernel-team Looks good.
Applied to the Vivid master-next branch.
diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c index 2e507b5..5460e65 100644 --- a/tools/perf/util/evlist.c +++ b/tools/perf/util/evlist.c @@ -635,11 +635,18 @@ 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]; - unsigned int head = perf_mmap__read_head(md); + unsigned int head; unsigned int 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 (!atomic_read(&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