On Thu, Feb 8, 2024 at 9:44 AM Namhyung Kim <namhyung@xxxxxxxxxx> wrote: > > Hi Ian, > > On Wed, Feb 7, 2024 at 2:37 PM Ian Rogers <irogers@xxxxxxxxxx> wrote: > > > > First 6 patches from: > > https://lore.kernel.org/lkml/20240202061532.1939474-1-irogers@xxxxxxxxxx/ > > > > v2. Fix NO_LIBUNWIND=1 build issue. > > > > Ian Rogers (6): > > perf maps: Switch from rbtree to lazily sorted array for addresses > > perf maps: Get map before returning in maps__find > > perf maps: Get map before returning in maps__find_by_name > > perf maps: Get map before returning in maps__find_next_entry > > perf maps: Hide maps internals > > perf maps: Locking tidy up of nr_maps > > Now I see a perf test failure on the vmlinux test: > > $ sudo ./perf test -v vmlinux > 1: vmlinux symtab matches kallsyms : > --- start --- > test child forked, pid 4164115 > /proc/{kallsyms,modules} inconsistency while looking for > "[__builtin__kprobes]" module! > /proc/{kallsyms,modules} inconsistency while looking for > "[__builtin__kprobes]" module! > /proc/{kallsyms,modules} inconsistency while looking for > "[__builtin__ftrace]" module! > Looking at the vmlinux_path (8 entries long) > Using /usr/lib/debug/boot/vmlinux-6.5.13-1rodete2-amd64 for symbols > perf: Segmentation fault > Obtained 16 stack frames. > ./perf(+0x1b7dcd) [0x55c40be97dcd] > ./perf(+0x1b7eb7) [0x55c40be97eb7] > /lib/x86_64-linux-gnu/libc.so.6(+0x3c510) [0x7f33d7a5a510] > ./perf(+0x1c2e9c) [0x55c40bea2e9c] > ./perf(+0x1c43f6) [0x55c40bea43f6] > ./perf(+0x1c4649) [0x55c40bea4649] > ./perf(+0x1c46d3) [0x55c40bea46d3] > ./perf(+0x1c7303) [0x55c40bea7303] > ./perf(+0x1c70b5) [0x55c40bea70b5] > ./perf(+0x1c73e6) [0x55c40bea73e6] > ./perf(+0x11833e) [0x55c40bdf833e] > ./perf(+0x118f78) [0x55c40bdf8f78] > ./perf(+0x103d49) [0x55c40bde3d49] > ./perf(+0x103e75) [0x55c40bde3e75] > ./perf(+0x1044c0) [0x55c40bde44c0] > ./perf(+0x104de0) [0x55c40bde4de0] > test child interrupted > ---- end ---- > vmlinux symtab matches kallsyms: FAILED! Ah, tripped over a latent bug summarized in this part of an asan stack trace: ``` freed by thread T0 here: #0 0x7fa13bcd74b5 in __interceptor_realloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:85 #1 0x561d66377713 in __maps__insert util/maps.c:353 #2 0x561d66377b89 in maps__insert util/maps.c:413 #3 0x561d6652911d in dso__process_kernel_symbol util/symbol-elf.c:1460 #4 0x561d6652aaae in dso__load_sym_internal util/symbol-elf.c:1675 #5 0x561d6652b6dc in dso__load_sym util/symbol-elf.c:1771 #6 0x561d66321a4e in dso__load util/symbol.c:1914 #7 0x561d66372cd9 in map__load util/map.c:353 #8 0x561d663730e7 in map__find_symbol_by_name_idx util/map.c:397 #9 0x561d663731e7 in map__find_symbol_by_name util/map.c:410 #10 0x561d66378208 in maps__find_symbol_by_name_cb util/maps.c:524 #11 0x561d66377f49 in maps__for_each_map util/maps.c:471 #12 0x561d663784a0 in maps__find_symbol_by_name util/maps.c:546 #13 0x561d662093e8 in machine__find_kernel_symbol_by_name util/machine.h:243 #14 0x561d6620abbd in test__vmlinux_matches_kallsyms tests/vmlinux-kallsyms.c:330 ... ``` dso__process_kernel_symbol rewrites the kernel maps here: https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/symbol-elf.c#n1378 which resizes the maps_by_address array causing the maps__for_each_map iteration in frame 11 to be iterating over a stale/freed value. The most correct solutions would be to clone the maps_by_address array prior to iteration, or reference count maps_by_address and its size. Neither of these solutions particularly appeal, so just reloading the maps_by_address and size on each iteration also fixes the problem, but possibly causes some maps to be skipped/repeated. I think this is acceptable correctness for the performance. Thanks, Ian > Thanks, > Namhyung
