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mount: disable mount-storm protection while mount unit is starting.

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The starting of mount units requires that changes to
/proc/self/mountinfo be processed before the SIGCHILD from the
completion of /sbin/mount is processed, as described by the comment
  /* Note that due to the io event priority logic, we can be sure the new mountinfo is loaded
   * before we process the SIGCHLD for the mount command. */

The recently-added mount-storm protection can defeat this as it
will sometimes deliberately delay processing of /proc/self/mountinfo.

So we need to disable mount-storm protection when a mount unit is starting.
We do this by keeping a counter of the number of pending
mounts, and disabling the protection when this is non-zero.

Thanks to @asavah for finding and reporting this problem.
This commit is contained in:
NeilBrown 2018-12-17 09:32:58 +11:00 committed by Lennart Poettering
parent ff03aee4b7
commit fcfb1f775e
2 changed files with 25 additions and 1 deletions
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1
src/core/manager.h
View File

@ -230,6 +230,7 @@ struct Manager {
sd_event_source *mount_timeout_source;
usec_t mount_last_read_usec;
usec_t mount_last_duration_usec;
unsigned mount_pending_count;
/* Data specific to the swap filesystem */
FILE *proc_swaps;

25
src/core/mount.c
View File

@ -218,6 +218,12 @@ static void mount_done(Unit *u) {
assert(m);
if (!IN_SET(m->state, MOUNT_DEAD, MOUNT_MOUNTED, MOUNT_FAILED)) {
/* This was pending, so need to udpate the count */
assert(u->manager->mount_pending_count > 0);
u->manager->mount_pending_count--;
}
m->where = mfree(m->where);
mount_parameters_done(&m->parameters_proc_self_mountinfo);
@ -650,6 +656,7 @@ static int mount_load(Unit *u) {
static void mount_set_state(Mount *m, MountState state) {
MountState old_state;
int was_pending, is_pending;
assert(m);
if (m->state != state)
@ -658,6 +665,17 @@ static void mount_set_state(Mount *m, MountState state) {
old_state = m->state;
m->state = state;
was_pending = !IN_SET(old_state, MOUNT_DEAD, MOUNT_MOUNTED, MOUNT_FAILED);
is_pending = !IN_SET(state, MOUNT_DEAD, MOUNT_MOUNTED, MOUNT_FAILED);
if (was_pending && !is_pending) {
assert(UNIT(m)->manager->mount_pending_count > 0);
UNIT(m)->manager->mount_pending_count--;
}
if (is_pending && !was_pending)
UNIT(m)->manager->mount_pending_count++;
if (!MOUNT_STATE_WITH_PROCESS(state)) {
m->timer_event_source = sd_event_source_unref(m->timer_event_source);
mount_unwatch_control_pid(m);
@ -1790,7 +1808,12 @@ static int mount_dispatch_io(sd_event_source *source, int fd, uint32_t revents,
usec_t next_read = usec_add(m->mount_last_read_usec,
m->mount_last_duration_usec * 10);
if (now(CLOCK_MONOTONIC) < next_read) {
/* If there are pending mounts initiated by systemd, then
* we need to process changes promptly, otherwise we
* rate limit re-reading the file.
*/
if (m->mount_pending_count == 0 &&
now(CLOCK_MONOTONIC) < next_read) {
/* The (current) API for getting mount events from the Linux kernel
* involves getting a "something changed" notification, and then having
* to re-read the entire /proc/self/mountinfo file. When there are lots