This is a note to let you know that I've just added the patch titled
perf lock contention: Fix core dump related to not finding the "__sched_text_end" symbol on s/390
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
perf-lock-contention-fix-core-dump-related-to-not-fi.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 7516ba3569b0d898f2d672aa28024f503b128fba
Author: Thomas Richter <tmricht@xxxxxxxxxxxxx>
Date: Fri Dec 30 11:26:27 2022 +0100
perf lock contention: Fix core dump related to not finding the "__sched_text_end" symbol on s/390
[ 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@xxxxxxxxxxxxx>
Acked-by: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Heiko Carstens <hca@xxxxxxxxxxxxx>
Cc: Sumanth Korikkar <sumanthk@xxxxxxxxxxxxx>
Cc: Sven Schnelle <svens@xxxxxxxxxxxxx>
Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20221230102627.2410847-1-tmricht@xxxxxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
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) {
