Messages in this thread Patch in this message |  | | From | Milos Vyletel <> | | Subject | [PATCH] perf: fix race in build_id_cache__add_s() | | Date | Fri, 20 Mar 2015 11:37:25 +0100 |
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int build_id_cache__add_s(const char *sbuild_id, const char *debugdir, const char *name, bool is_kallsyms, bool is_vdso) { ... if (access(filename, F_OK)) { ^--------------------------------------------------------- [1] if (is_kallsyms) { if (copyfile("/proc/kallsyms", filename)) goto out_free; } else if (link(realname, filename) && copyfile(name, filename)) ^-----------------------------^------------- [2] \------------ [3] goto out_free; } ...
when multiple instances of perf record get to [1] at more or less same time and run access() one or more may get failure because the file does not exist yet (since the first instance did not have chance to link it yet). at this point the race moves to link() at [2] where first thread to get there links file and goes on but second one gets -EEXIST so it runs copyfile [3] which truncates the file.
recreator: rm -rf /root/.debug for cpu in $(awk '/processor/ {print $3}' /proc/cpuinfo); do perf record -a -v -T -F 1000 -C $cpu \ -o perf-${cpu}.data sleep 5 2> /dev/null & done wait
and simply search for empty files by find /lib/modules/`uname -r`/kernel/* -size 0
Signed-off-by: Milos Vyletel <milos@redhat.com> --- tools/perf/util/build-id.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/tools/perf/util/build-id.c b/tools/perf/util/build-id.c index 0c72680..a9db5a1 100644 --- a/tools/perf/util/build-id.c +++ b/tools/perf/util/build-id.c @@ -293,7 +293,8 @@ int build_id_cache__add_s(const char *sbuild_id, const char *debugdir, if (is_kallsyms) { if (copyfile("/proc/kallsyms", filename)) goto out_free; - } else if (link(realname, filename) && copyfile(name, filename)) + } else if (link(realname, filename) && errno != EEXIST && + copyfile(name, filename)) goto out_free; } -- 2.1.0
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