From: Thomas Richter tmricht@linux.ibm.com
[ Upstream commit d8d85ce86dc82de4f88b821a78f533b9d5b22a45 ]
The test case perf lock contention dumps core on s390. Run the following commands:
# ./perf lock record -- ./perf bench sched messaging # Running 'sched/messaging' benchmark: # 20 sender and receiver processes per group # 10 groups == 400 processes run
Total time: 2.799 [sec] [ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 0.073 MB perf.data (100 samples) ] # # ./perf lock contention Segmentation fault (core dumped) #
The function call stack is lengthy, here are the top 5 functions:
# gdb ./perf core.24048 GNU gdb (GDB) Fedora Linux 12.1-6.fc37 Core was generated by `./perf lock contention'. Program terminated with signal SIGSEGV, Segmentation fault. #0 0x00000000011dd25c in machine__is_lock_function (machine=0x3029e28, addr=1789230) at util/machine.c:3356 3356 machine->sched.text_end = kmap->unmap_ip(kmap, sym->start);
(gdb) where #0 0x00000000011dd25c in machine__is_lock_function (machine=0x3029e28, addr=1789230) at util/machine.c:3356 #1 0x000000000109f244 in callchain_id (evsel=0x30313e0, sample=0x3ffea4f77d0) at builtin-lock.c:957 #2 0x000000000109e094 in get_key_by_aggr_mode (key=0x3ffea4f7290, addr=27758136, evsel=0x30313e0, sample=0x3ffea4f77d0) at builtin-lock.c:586 #3 0x000000000109f4d0 in report_lock_contention_begin_event (evsel=0x30313e0, sample=0x3ffea4f77d0) at builtin-lock.c:1004 #4 0x00000000010a00ae in evsel__process_contention_begin (evsel=0x30313e0, sample=0x3ffea4f77d0) at builtin-lock.c:1254 #5 0x00000000010a0e14 in process_sample_event (tool=0x3ffea4f8480, event=0x3ff85601ef8, sample=0x3ffea4f77d0, evsel=0x30313e0, machine=0x3029e28) at builtin-lock.c:1464 .....
The issue is in function machine__is_lock_function() in file ./util/machine.c lines 3355:
/* should not fail from here */ sym = machine__find_kernel_symbol_by_name(machine, "__sched_text_end", &kmap); machine->sched.text_end = kmap->unmap_ip(kmap, sym->start)
On s390 the symbol __sched_text_end is *NOT* in the symbol list and the resulting pointer sym is set to NULL. The sym->start is then a NULL pointer access and generates the core dump.
The reason why __sched_text_end is not in the symbol list on s390 is simple:
When the symbol list is created at perf start up with function calls
dso__load +--> dso__load_vmlinux_path +--> dso__load_vmlinux +--> dso__load_sym +--> dso__load_sym_internal (reads kernel symbols) +--> symbols__fixup_end +--> symbols__fixup_duplicate
The issue is in function symbols__fixup_duplicate(). It deletes all symbols with have the same address. On s390:
# nm -g ~/linux/vmlinux| fgrep c68390 0000000000c68390 T __cpuidle_text_start 0000000000c68390 T __sched_text_end #
two symbols have identical addresses and __sched_text_end is considered duplicate (in ascending sort order) and removed from the symbol list. Therefore it is missing and an invalid pointer reference occurs. The code checks for symbol __sched_text_start and when it exists assumes symbol __sched_text_end is also in the symbol table. However this is not the case on s390.
Same situation exists for symbol __lock_text_start:
0000000000c68770 T __cpuidle_text_end 0000000000c68770 T __lock_text_start
This symbol is also removed from the symbol table but used in function machine__is_lock_function().
To fix this and keep duplicate symbols in the symbol table, set symbol_conf.allow_aliases to true. This prevents the removal of duplicate symbols in function symbols__fixup_duplicate().
Output After:
# ./perf lock contention contended total wait max wait avg wait type caller
48 124.39 ms 123.99 ms 2.59 ms rwsem:W unlink_anon_vmas+0x24a 47 83.68 ms 83.26 ms 1.78 ms rwsem:W free_pgtables+0x132 5 41.22 us 10.55 us 8.24 us rwsem:W free_pgtables+0x140 4 40.12 us 20.55 us 10.03 us rwsem:W copy_process+0x1ac8 #
Fixes: 0d2997f750d1de39 ("perf lock: Look up callchain for the contended locks") Signed-off-by: Thomas Richter tmricht@linux.ibm.com Acked-by: Namhyung Kim namhyung@kernel.org Cc: Heiko Carstens hca@linux.ibm.com Cc: Sumanth Korikkar sumanthk@linux.ibm.com Cc: Sven Schnelle svens@linux.ibm.com Cc: Vasily Gorbik gor@linux.ibm.com Link: https://lore.kernel.org/r/20221230102627.2410847-1-tmricht@linux.ibm.com Signed-off-by: Arnaldo Carvalho de Melo acme@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- tools/perf/builtin-lock.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/tools/perf/builtin-lock.c b/tools/perf/builtin-lock.c index 66520712a167..470106643ed5 100644 --- a/tools/perf/builtin-lock.c +++ b/tools/perf/builtin-lock.c @@ -1582,6 +1582,7 @@ static int __cmd_report(bool display_info)
/* for lock function check */ symbol_conf.sort_by_name = true; + symbol_conf.allow_aliases = true; symbol__init(&session->header.env);
if (!perf_session__has_traces(session, "lock record")) @@ -1660,6 +1661,7 @@ static int __cmd_contention(int argc, const char **argv)
/* for lock function check */ symbol_conf.sort_by_name = true; + symbol_conf.allow_aliases = true; symbol__init(&session->header.env);
if (use_bpf) {