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Merge pull request #13097 from poettering/mount-state-fix

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Scan /proc/self/mountinfo before waitid() handling
This commit is contained in:
Zbigniew Jędrzejewski-Szmek
2019-07-18 17:33:20 +02:00
committed by GitHub
parent f4c961169c 9ddaa3e459
commit deeabb45ae
2 changed files with 72 additions and 32 deletions
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86
src/core/mount.c
View File

@@ -50,6 +50,7 @@ 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,
@@ -232,7 +233,7 @@ _pure_ static MountParameters* get_mount_parameters(Mount *m) {
return get_mount_parameters_fragment(m);
}
static int update_parameters_proc_self_mount_info(
static int update_parameters_proc_self_mountinfo(
Mount *m,
const char *what,
const char *options,
@@ -1280,6 +1281,22 @@ 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))
@@ -1468,7 +1485,7 @@ static int mount_setup_new_unit(
if (r < 0)
return r;
r = update_parameters_proc_self_mount_info(MOUNT(u), what, options, fstype);
r = update_parameters_proc_self_mountinfo(MOUNT(u), what, options, fstype);
if (r < 0)
return r;
@@ -1506,7 +1523,7 @@ static int mount_setup_existing_unit(
return -ENOMEM;
}
r = update_parameters_proc_self_mount_info(MOUNT(u), what, options, fstype);
r = update_parameters_proc_self_mountinfo(MOUNT(u), what, options, fstype);
if (r < 0)
return r;
if (r > 0)
@@ -1751,39 +1768,41 @@ fail:
mount_shutdown(m);
}
static int mount_dispatch_io(sd_event_source *source, int fd, uint32_t revents, void *userdata) {
static int drain_libmount(Manager *m) {
bool rescan = false;
int r;
assert(m);
/* Drain all events and verify that the event is valid.
*
* Note that libmount also monitors /run/mount mkdir if the directory does not exist yet. The mkdir
* may generate event which is irrelevant for us.
*
* error: r < 0; valid: r == 0, false positive: r == 1 */
do {
r = mnt_monitor_next_change(m->mount_monitor, NULL, NULL);
if (r < 0)
return log_error_errno(r, "Failed to drain libmount events: %m");
if (r == 0)
rescan = true;
} while (r == 0);
return rescan;
}
static int mount_process_proc_self_mountinfo(Manager *m) {
_cleanup_set_free_free_ Set *around = NULL, *gone = NULL;
Manager *m = userdata;
const char *what;
Iterator i;
Unit *u;
int r;
assert(m);
assert(revents & EPOLLIN);
if (fd == mnt_monitor_get_fd(m->mount_monitor)) {
bool rescan = false;
/* Drain all events and verify that the event is valid.
*
* Note that libmount also monitors /run/mount mkdir if the
* directory does not exist yet. The mkdir may generate event
* which is irrelevant for us.
*
* error: r < 0; valid: r == 0, false positive: rc == 1 */
do {
r = mnt_monitor_next_change(m->mount_monitor, NULL, NULL);
if (r == 0)
rescan = true;
else if (r < 0)
return log_error_errno(r, "Failed to drain libmount events: %m");
} while (r == 0);
log_debug("libmount event [rescan: %s]", yes_no(rescan));
if (!rescan)
return 0;
}
r = drain_libmount(m);
if (r <= 0)
return r;
r = mount_load_proc_self_mountinfo(m, true);
if (r < 0) {
@@ -1815,7 +1834,7 @@ static int mount_dispatch_io(sd_event_source *source, int fd, uint32_t revents,
}
mount->from_proc_self_mountinfo = false;
assert_se(update_parameters_proc_self_mount_info(mount, NULL, NULL, NULL) >= 0);
assert_se(update_parameters_proc_self_mountinfo(mount, NULL, NULL, NULL) >= 0);
switch (mount->state) {
@@ -1884,6 +1903,15 @@ 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);

18
src/core/swap.c
View File

@@ -43,6 +43,7 @@ static const UnitActiveState state_translation_table[_SWAP_STATE_MAX] = {
static int swap_dispatch_timer(sd_event_source *source, usec_t usec, void *userdata);
static int swap_dispatch_io(sd_event_source *source, int fd, uint32_t revents, void *userdata);
static int swap_process_proc_swaps(Manager *m);
static bool SWAP_STATE_WITH_PROCESS(SwapState state) {
return IN_SET(state,
@@ -1014,6 +1015,10 @@ static void swap_sigchld_event(Unit *u, pid_t pid, int code, int status) {
if (pid != s->control_pid)
return;
/* Let's scan /proc/swaps before we process SIGCHLD. For the reasoning see the similar code in
* mount.c */
(void) swap_process_proc_swaps(u->manager);
s->control_pid = 0;
if (is_clean_exit(code, status, EXIT_CLEAN_COMMAND, NULL))
@@ -1149,13 +1154,11 @@ static int swap_load_proc_swaps(Manager *m, bool set_flags) {
return 0;
}
static int swap_dispatch_io(sd_event_source *source, int fd, uint32_t revents, void *userdata) {
Manager *m = userdata;
static int swap_process_proc_swaps(Manager *m) {
Unit *u;
int r;
assert(m);
assert(revents & EPOLLPRI);
r = swap_load_proc_swaps(m, true);
if (r < 0) {
@@ -1230,6 +1233,15 @@ static int swap_dispatch_io(sd_event_source *source, int fd, uint32_t revents, v
return 1;
}
static int swap_dispatch_io(sd_event_source *source, int fd, uint32_t revents, void *userdata) {
Manager *m = userdata;
assert(m);
assert(revents & EPOLLPRI);
return swap_process_proc_swaps(m);
}
static Unit *swap_following(Unit *u) {
Swap *s = SWAP(u);
Swap *other, *first = NULL;