perf record: Fix event fd races

The write call may set errno which is problematic if occurring in a
function also setting errno. Save and restore errno around the write
call.

done_fd may be used after close, clear it as part of the close and check
its validity in the signal handler.

Suggested-by: <gthelen@google.com>
Reviewed-by: Leo Yan <leo.yan@linaro.org>
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Anand K Mistry <amistry@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: https://lore.kernel.org/r/20221024011024.462518-1-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 52d254b..e128b85 100644 (file)
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -649,7 +649,7 @@ static int record__pushfn(struct mmap *map, void *to, void *bf, size_t size)
 static volatile int signr = -1;
 static volatile int child_finished;
 #ifdef HAVE_EVENTFD_SUPPORT
-static int done_fd = -1;
+static volatile int done_fd = -1;
 #endif
 
 static void sig_handler(int sig)
@@ -661,19 +661,24 @@ static void sig_handler(int sig)
 
        done = 1;
 #ifdef HAVE_EVENTFD_SUPPORT
-{
-       u64 tmp = 1;
-       /*
-        * It is possible for this signal handler to run after done is checked
-        * in the main loop, but before the perf counter fds are polled. If this
-        * happens, the poll() will continue to wait even though done is set,
-        * and will only break out if either another signal is received, or the
-        * counters are ready for read. To ensure the poll() doesn't sleep when
-        * done is set, use an eventfd (done_fd) to wake up the poll().
-        */
-       if (write(done_fd, &tmp, sizeof(tmp)) < 0)
-               pr_err("failed to signal wakeup fd, error: %m\n");
-}
+       if (done_fd >= 0) {
+               u64 tmp = 1;
+               int orig_errno = errno;
+
+               /*
+                * It is possible for this signal handler to run after done is
+                * checked in the main loop, but before the perf counter fds are
+                * polled. If this happens, the poll() will continue to wait
+                * even though done is set, and will only break out if either
+                * another signal is received, or the counters are ready for
+                * read. To ensure the poll() doesn't sleep when done is set,
+                * use an eventfd (done_fd) to wake up the poll().
+                */
+               if (write(done_fd, &tmp, sizeof(tmp)) < 0)
+                       pr_err("failed to signal wakeup fd, error: %m\n");
+
+               errno = orig_errno;
+       }
 #endif // HAVE_EVENTFD_SUPPORT
 }
 
@@ -2834,8 +2839,12 @@ out_free_threads:
 
 out_delete_session:
 #ifdef HAVE_EVENTFD_SUPPORT
-       if (done_fd >= 0)
-               close(done_fd);
+       if (done_fd >= 0) {
+               fd = done_fd;
+               done_fd = -1;
+
+               close(fd);
+       }
 #endif
        zstd_fini(&session->zstd_data);
        perf_session__delete(session);