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author | Lennart Poettering <lennart@poettering.net> | 2019-07-17 18:57:13 +0200 |
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committer | The Plumber <50238977+systemd-rhel-bot@users.noreply.github.com> | 2019-08-07 14:20:15 +0200 |
commit | 4bc21bbc61acd1ce114da381a9742f6bcd4ffde8 (patch) | |
tree | 849d1c3b9b1cb5072849fdcaec267af5498c846d | |
parent | daf63a3c6c6cd241017bdf9a26c7b1caf744e69b (diff) | |
download | systemd-4bc21bbc61acd1ce114da381a9742f6bcd4ffde8.tar.gz |
mount: rescan /proc/self/mountinfo before processing waitid() results
(The interesting bits about the what and why are in a comment in the
patch, please have a look there instead of looking here in the commit
msg).
Fixes: #10872
(cherry picked from commit 350804867dbcc9b7ccabae1187d730d37e2d8a21)
Conflicts:
src/core/mount.c
Resolves: #1696178
-rw-r--r-- | src/core/mount.c | 30 |
1 files changed, 27 insertions, 3 deletions
diff --git a/src/core/mount.c b/src/core/mount.c index 85b07375e2..2ac04e3874 100644 --- a/src/core/mount.c +++ b/src/core/mount.c @@ -53,6 +53,7 @@ static const UnitActiveState state_translation_table[_MOUNT_STATE_MAX] = { static int mount_dispatch_timer(sd_event_source *source, usec_t usec, void *userdata); static int mount_dispatch_io(sd_event_source *source, int fd, uint32_t revents, void *userdata); +static int mount_process_proc_self_mountinfo(Manager *m); static bool MOUNT_STATE_WITH_PROCESS(MountState state) { return IN_SET(state, @@ -1241,6 +1242,22 @@ static void mount_sigchld_event(Unit *u, pid_t pid, int code, int status) { if (pid != m->control_pid) return; + /* So here's the thing, we really want to know before /usr/bin/mount or /usr/bin/umount exit whether + * they established/remove a mount. This is important when mounting, but even more so when unmounting + * since we need to deal with nested mounts and otherwise cannot safely determine whether to repeat + * the unmounts. In theory, the kernel fires /proc/self/mountinfo changes off before returning from + * the mount() or umount() syscalls, and thus we should see the changes to the proc file before we + * process the waitid() for the /usr/bin/(u)mount processes. However, this is unfortunately racy: we + * have to waitid() for processes using P_ALL (since we need to reap unexpected children that got + * reparented to PID 1), but when using P_ALL we might end up reaping processes that terminated just + * instants ago, i.e. already after our last event loop iteration (i.e. after the last point we might + * have noticed /proc/self/mountinfo events via epoll). This means event loop priorities for + * processing SIGCHLD vs. /proc/self/mountinfo IO events are not as relevant as we want. To fix that + * race, let's explicitly scan /proc/self/mountinfo before we start processing /usr/bin/(u)mount + * dying. It's ugly, but it makes our ordering systematic again, and makes sure we always see + * /proc/self/mountinfo changes before our mount/umount exits. */ + (void) mount_process_proc_self_mountinfo(u->manager); + m->control_pid = 0; if (is_clean_exit(code, status, EXIT_CLEAN_COMMAND, NULL)) @@ -1781,16 +1798,14 @@ static int drain_libmount(Manager *m) { return rescan; } -static int mount_dispatch_io(sd_event_source *source, int fd, uint32_t revents, void *userdata) { +static int mount_process_proc_self_mountinfo(Manager *m) { _cleanup_set_free_ Set *around = NULL, *gone = NULL; - Manager *m = userdata; const char *what; Iterator i; Unit *u; int r; assert(m); - assert(revents & EPOLLIN); r = drain_libmount(m); if (r <= 0) @@ -1898,6 +1913,15 @@ static int mount_dispatch_io(sd_event_source *source, int fd, uint32_t revents, return 0; } +static int mount_dispatch_io(sd_event_source *source, int fd, uint32_t revents, void *userdata) { + Manager *m = userdata; + + assert(m); + assert(revents & EPOLLIN); + + return mount_process_proc_self_mountinfo(m); +} + static void mount_reset_failed(Unit *u) { Mount *m = MOUNT(u); |