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From 2d8d8b2d713a3b0c0aad0552608cc2cd13583207 Mon Sep 17 00:00:00 2001
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From: Michal Sekletar <msekleta@redhat.com>
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Date: Fri, 26 Apr 2019 19:20:09 +0200
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Subject: [PATCH] udev: check if the spawned PID didn't exit after reaping
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unexpected PID
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We shouldn't just continue after getting SIGCHLD for the unexpected
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process because signal coalescing might have happened. If it actually
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did happen we won't get any more SIGCHLDs on signalfd.
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Related: #1697909
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---
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src/udev/udev-event.c | 27 +++++++++++++++++++++++----
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1 file changed, 23 insertions(+), 4 deletions(-)
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diff --git a/src/udev/udev-event.c b/src/udev/udev-event.c
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index 0ba079201c..7fe64f04a4 100644
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--- a/src/udev/udev-event.c
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+++ b/src/udev/udev-event.c
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@@ -597,8 +597,9 @@ static int spawn_wait(struct udev_event *event,
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}
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if (pfd[0].revents & POLLIN) {
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+ int child_exited = -1;
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struct signalfd_siginfo fdsi;
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- int status;
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+ int status, r;
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ssize_t size;
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size = read(event->fd_signal, &fdsi, sizeof(struct signalfd_siginfo));
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@@ -612,10 +613,28 @@ static int spawn_wait(struct udev_event *event,
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case SIGCHLD:
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if (pid != (pid_t) fdsi.ssi_pid) {
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log_debug("expected SIGCHLD from '%s' ["PID_FMT"] received from unknown process ["PID_FMT"]. Ignoring", cmd, pid, fdsi.ssi_pid);
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- continue;
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+
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+ /* We got SIGCHLD from unexpected process. Possibly some library that we use forked off something behind our back.
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+ In case the PID we wait for also exited the kernel could coalesce SIGCHLDs and we won't get second SIGCHLD
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+ on the signalfd. We can't know if coalescing happened or not, hence we need to call waitpid() in a loop until
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+ the PID we care for exits, we if it haven't already. */
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+ while (child_exited < 0) {
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+ r = waitpid(-1, &status, 0);
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+ if (r < 0 && errno == EINTR)
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+ continue;
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+ else if (r < 0)
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+ break;
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+ else if (r == pid)
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+ child_exited = 0;
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+ }
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}
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- if (waitpid(pid, &status, WNOHANG) <= 0)
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- break;
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+
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+ /* We didn't wait for child yet, let's do that now */
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+ if (child_exited < 0) {
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+ if (waitpid(pid, &status, WNOHANG) <= 0)
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+ break;
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+ }
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+
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if (WIFEXITED(status)) {
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log_debug("'%s' ["PID_FMT"] exit with return code %i", cmd, pid, WEXITSTATUS(status));
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if (WEXITSTATUS(status) != 0)
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