Messages in this thread | | | From | Namhyung Kim <> | Date | Tue, 3 Jan 2023 08:45:34 -0800 | Subject | Re: [PATCH] perf lock: Fix core dump in command perf lock contention |
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Hi Arnaldo,
On Mon, Jan 2, 2023 at 7:33 AM Arnaldo Carvalho de Melo <acme@kernel.org> wrote: > > Em Fri, Dec 30, 2022 at 11:26:27AM +0100, Thomas Richter escreveu: > > 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 > > Copyright (C) 2022 Free Software Foundation, Inc. > > 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 > > sample=0x3ffea4f77d0, evsel=0x30313e0, machine=0x3029e28) \ > > at util/session.c:1523 > > ..... > > > > 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: cc2367eebb0c ("machine: Adopt is_lock_function() from builtin-lock.c") > > Humm, is that really the cset that introduces the problem? It just moves > things around, the cset that introduced the is_lock_function() function, > that assumed that __sched_text_end was always available was: > > commit 0d2997f750d1de394231bc22768dab94a5b5db2f > Author: Namhyung Kim <namhyung@kernel.org> > Date: Wed Jun 15 09:32:22 2022 -0700 > > perf lock: Look up callchain for the contended locks > > --- > > Right? Namhyung? Can you spot any problem in enabling duplicates as a > fix?
Yep, I think that's the cset introduced the problem. I'm fine with the fix.
Acked-by: Namhyung Kim <namhyung@kernel.org>
Thanks, Namhyung
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