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SubjectRe: [PATCH] perf mmap: Fix accessing unmapped mmap in perf_mmap__read_done()
Em Mon, Mar 26, 2018 at 11:26:04AM -0300, Arnaldo Carvalho de Melo escreveu:
> Em Mon, Mar 26, 2018 at 09:42:09AM -0400, kan.liang@linux.intel.com escreveu:
> > From: Kan Liang <kan.liang@linux.intel.com>
> >
> > There is segmentation fault when running perf trace. For example,
> > [root@jouet e]# perf trace -e *chdir -o /tmp/bla perf report
> > --ignore-vmlinux -i ../perf.data
> >
> > The perf_mmap__consume() could unmap the mmap. It needs to check the
> > refcnt in perf_mmap__read_done().
> >
> > Fixes: ee023de05f35 ("perf mmap: Introduce perf_mmap__read_done()")
> > Reported-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> > Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
>
> Seems insuficient:
>
> [root@jouet ~]# perf trace -e *chdir -o /tmp/bla perf report --ignore-vmlinux
> perf: Segmentation fault
> Obtained 9 stack frames.
> perf(sighandler_dump_stack+0x3e) [0x4fe31e]
> /lib64/libc.so.6(+0x346df) [0x7fc0c3ced6df]
> perf(perf_mmap__read_init+0x26) [0x4ccd06]
> perf(cmd_trace+0x1bf6) [0x47bb76]
> perf() [0x4a824e]
> perf() [0x4a8550]
> perf(main+0x331) [0x42bef1]
> /lib64/libc.so.6(__libc_start_main+0xe9) [0x7fc0c3cd9f29]
> perf(_start+0x29) [0x42c319]
> Segmentation fault (core dumped)
> [root@jouet ~]#

I'm adding this as a separate patch, with yours and this one, the
segfault is gone.

- Arnaldo

diff --git a/tools/perf/util/mmap.c b/tools/perf/util/mmap.c
index f6cfc52ff1fe..fc832676a798 100644
--- a/tools/perf/util/mmap.c
+++ b/tools/perf/util/mmap.c
@@ -234,7 +234,7 @@ static int overwrite_rb_find_range(void *buf, int mask, u64 *start, u64 *end)
/*
* Report the start and end of the available data in ringbuffer
*/
-int perf_mmap__read_init(struct perf_mmap *md)
+static int __perf_mmap__read_init(struct perf_mmap *md)
{
u64 head = perf_mmap__read_head(md);
u64 old = md->prev;
@@ -268,6 +268,17 @@ int perf_mmap__read_init(struct perf_mmap *md)
return 0;
}

+int perf_mmap__read_init(struct perf_mmap *map)
+{
+ /*
+ * Check if event was unmapped due to a POLLHUP/POLLERR.
+ */
+ if (!refcount_read(&map->refcnt))
+ return -ENOENT;
+
+ return __perf_mmap__read_init(map);
+}
+
int perf_mmap__push(struct perf_mmap *md, void *to,
int push(void *to, void *buf, size_t size))
{
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