[PATCH] perf comm str: Fix perf top coredump due to concurrent read and write

[Fei Lang]

(gdb) bt
    __strcmp_evex () at ../sysdeps/x86_64/multiarch/strcmp-evex.S:314
    sort.comm_collapse () at util/sort.c:202
    hist_entry__collapse at util/hist.c:1312
    hists__collapse_insert_entry at util/hist.c:1620
    hists__collapse_resort at util/hist.c:1704
    perf_top__resort_hists at builtin-top.c:303
    perf_top__print_sym_table at builtin-top.c:350
    display_thread at builtin-top.c:700

Link:https://bugzilla.kernel.org/show_bug.cgi?id=220096

Fixes: <3178f58b9894> ("perf comm str: Avoid sort during insert")
Signed-off-by: Fei Lang <langfei@xxxxxxxxxx>
---
 tools/perf/util/comm.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/comm.c b/tools/perf/util/comm.c
index 8aa456d7c2cd..0438870d31d2 100644
--- a/tools/perf/util/comm.c
+++ b/tools/perf/util/comm.c
@@ -209,13 +209,16 @@ struct comm *comm__new(const char *str, u64 timestamp, bool exec)
 int comm__override(struct comm *comm, const char *str, u64 timestamp, bool exec)
 {
 	struct comm_str *new, *old = comm->comm_str;
+	struct comm_strs *comm_strs = comm_strs__get();
 
 	new = comm_strs__findnew(str);
 	if (!new)
 		return -ENOMEM;
 
+	down_write(&comm_strs->lock);
 	comm_str__put(old);
 	comm->comm_str = new;
+	up_write(&comm_strs->lock);
 	comm->start = timestamp;
 	if (exec)
 		comm->exec = true;
@@ -225,11 +228,22 @@ int comm__override(struct comm *comm, const char *str, u64 timestamp, bool exec)
 
 void comm__free(struct comm *comm)
 {
+	struct comm_strs *comm_strs = comm_strs__get();
+
+	down_write(&comm_strs->lock);
 	comm_str__put(comm->comm_str);
 	free(comm);
+	up_write(&comm_strs->lock);
 }
 
 const char *comm__str(const struct comm *comm)
 {
-	return comm_str__str(comm->comm_str);
+	struct comm_strs *comm_strs = comm_strs__get();
+	char *p;
+
+	down_read(&comm_strs->lock);
+	p = comm_str__str(comm->comm_str);
+	up_read(&comm_strs->lock);
+
+	return p;
 }
-- 
2.33.0