Messages in this thread Patch in this message | | | Date | Fri, 8 May 2020 14:56:43 +1000 | Subject | [PATCH] perf record: Use an eventfd to wakeup when done | From | Anand K Mistry <> |
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The setting and checking of 'done' contains a rare race where the signal handler setting 'done' is run after checking to break the loop, but before waiting in evlist__poll(). In this case, the main loop won't wake up until either another signal is sent, or the perf data fd causes a wake up.
The following simple script can trigger this condition (but you might need to run it for several hours): for ((i = 0; i >= 0; i++)) ; do echo "Loop $i" delay=$(echo "scale=4; 0.1 * $RANDOM/32768" | bc) ./perf record -- sleep 30000000 >/dev/null& pid=$! sleep $delay kill -TERM $pid echo "PID $pid" wait $pid done
At some point, the loop will stall. Adding logging, even though perf has received the SIGTERM and set 'done = 1', perf will remain sleeping until a second signal is sent.
Signed-off-by: Anand K Mistry <amistry@google.com>
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tools/perf/builtin-record.c | 8 ++++++++ 1 file changed, 8 insertions(+)
diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c index 1ab349abe90469..ce5fc3860131d2 100644 --- a/tools/perf/builtin-record.c +++ b/tools/perf/builtin-record.c @@ -53,6 +53,7 @@ #include <unistd.h> #include <sched.h> #include <signal.h> +#include <sys/eventfd.h> #include <sys/mman.h> #include <sys/wait.h> #include <sys/types.h> @@ -518,15 +519,19 @@ static int record__pushfn(struct mmap *map, void *to, void *bf, size_t size) static volatile int signr = -1; static volatile int child_finished; +static int done_fd = -1; static void sig_handler(int sig) { + u64 tmp = 1; if (sig == SIGCHLD) child_finished = 1; else signr = sig; done = 1; + if (write(done_fd, &tmp, sizeof(tmp)) < 0) + pr_err("failed to signal wakeup fd\n"); } static void sigsegv_handler(int sig) @@ -1424,6 +1429,9 @@ static int __cmd_record(struct record *rec, int argc, const char **argv) int fd; float ratio = 0; + done_fd = eventfd(0, EFD_NONBLOCK); + evlist__add_pollfd(rec->evlist, done_fd); + atexit(record__sig_exit); signal(SIGCHLD, sig_handler); signal(SIGINT, sig_handler); -- 2.26.2.645.ge9eca65c58-goog
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