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Subject[tip: perf/urgent] perf probe: Fix to clear tev->nargs in clear_probe_trace_event()
The following commit has been merged into the perf/urgent branch of tip:

Commit-ID: 9e6124d9d635957b56717f85219a88701617253f
Gitweb: https://git.kernel.org/tip/9e6124d9d635957b56717f85219a88701617253f
Author: Masami Hiramatsu <mhiramat@kernel.org>
AuthorDate: Mon, 16 Sep 2019 01:44:40 +09:00
Committer: Arnaldo Carvalho de Melo <acme@redhat.com>
CommitterDate: Fri, 20 Sep 2019 15:30:09 -03:00

perf probe: Fix to clear tev->nargs in clear_probe_trace_event()

Since add_probe_trace_event() can reuse tf->tevs[i] after calling
clear_probe_trace_event(), this can make perf-probe crash if the 1st
attempt of probe event finding fails to find an event argument, and the
2nd attempt fails to find probe point.

E.g.
$ perf probe -D "task_pid_nr tsk"
Failed to find 'tsk' in this function.
Failed to get entry address of warn_bad_vsyscall
Segmentation fault (core dumped)

Committer testing:

After the patch:

$ perf probe -D "task_pid_nr tsk"
Failed to find 'tsk' in this function.
Failed to get entry address of warn_bad_vsyscall
Failed to get entry address of signal_fault
Failed to get entry address of show_signal
Failed to get entry address of umip_printk
Failed to get entry address of __bad_area_nosemaphore
<SNIP>
Failed to get entry address of sock_set_timeout
Failed to get entry address of tcp_recvmsg
Probe point 'task_pid_nr' not found.
Error: Failed to add events.
$

Fixes: 092b1f0b5f9f ("perf probe: Clear probe_trace_event when add_probe_trace_event() fails")
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lore.kernel.org/lkml/156856587999.25775.5145779959474477595.stgit@devnote2
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/util/probe-event.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/tools/perf/util/probe-event.c b/tools/perf/util/probe-event.c
index b8e0967..91cab5f 100644
--- a/tools/perf/util/probe-event.c
+++ b/tools/perf/util/probe-event.c
@@ -2331,6 +2331,7 @@ void clear_probe_trace_event(struct probe_trace_event *tev)
}
}
zfree(&tev->args);
+ tev->nargs = 0;
}

struct kprobe_blacklist_node {
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