On Fri, Mar 20, 2015 at 11:37:25AM +0100, Milos Vyletel wrote:
> 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.
nice.. :-\
Acked-by: Jiri Olsa <[email protected]>
in addition we should use some inter-perf lock
on all .debug dir operations
jirka
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