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91 lines
3.9 KiB
91 lines
3.9 KiB
From 4bc21bbc61acd1ce114da381a9742f6bcd4ffde8 Mon Sep 17 00:00:00 2001
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From: Lennart Poettering <lennart@poettering.net>
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Date: Wed, 17 Jul 2019 18:57:13 +0200
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Subject: [PATCH] mount: rescan /proc/self/mountinfo before processing waitid()
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results
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(The interesting bits about the what and why are in a comment in the
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patch, please have a look there instead of looking here in the commit
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msg).
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Fixes: #10872
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(cherry picked from commit 350804867dbcc9b7ccabae1187d730d37e2d8a21)
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Conflicts:
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src/core/mount.c
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Resolves: #1696178
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---
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src/core/mount.c | 30 +++++++++++++++++++++++++++---
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1 file changed, 27 insertions(+), 3 deletions(-)
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diff --git a/src/core/mount.c b/src/core/mount.c
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index 85b07375e2..2ac04e3874 100644
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--- a/src/core/mount.c
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+++ b/src/core/mount.c
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@@ -53,6 +53,7 @@ static const UnitActiveState state_translation_table[_MOUNT_STATE_MAX] = {
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static int mount_dispatch_timer(sd_event_source *source, usec_t usec, void *userdata);
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static int mount_dispatch_io(sd_event_source *source, int fd, uint32_t revents, void *userdata);
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+static int mount_process_proc_self_mountinfo(Manager *m);
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static bool MOUNT_STATE_WITH_PROCESS(MountState state) {
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return IN_SET(state,
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@@ -1241,6 +1242,22 @@ static void mount_sigchld_event(Unit *u, pid_t pid, int code, int status) {
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if (pid != m->control_pid)
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return;
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+ /* So here's the thing, we really want to know before /usr/bin/mount or /usr/bin/umount exit whether
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+ * they established/remove a mount. This is important when mounting, but even more so when unmounting
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+ * since we need to deal with nested mounts and otherwise cannot safely determine whether to repeat
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+ * the unmounts. In theory, the kernel fires /proc/self/mountinfo changes off before returning from
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+ * the mount() or umount() syscalls, and thus we should see the changes to the proc file before we
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+ * process the waitid() for the /usr/bin/(u)mount processes. However, this is unfortunately racy: we
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+ * have to waitid() for processes using P_ALL (since we need to reap unexpected children that got
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+ * reparented to PID 1), but when using P_ALL we might end up reaping processes that terminated just
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+ * instants ago, i.e. already after our last event loop iteration (i.e. after the last point we might
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+ * have noticed /proc/self/mountinfo events via epoll). This means event loop priorities for
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+ * processing SIGCHLD vs. /proc/self/mountinfo IO events are not as relevant as we want. To fix that
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+ * race, let's explicitly scan /proc/self/mountinfo before we start processing /usr/bin/(u)mount
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+ * dying. It's ugly, but it makes our ordering systematic again, and makes sure we always see
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+ * /proc/self/mountinfo changes before our mount/umount exits. */
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+ (void) mount_process_proc_self_mountinfo(u->manager);
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+
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m->control_pid = 0;
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if (is_clean_exit(code, status, EXIT_CLEAN_COMMAND, NULL))
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@@ -1781,16 +1798,14 @@ static int drain_libmount(Manager *m) {
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return rescan;
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}
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-static int mount_dispatch_io(sd_event_source *source, int fd, uint32_t revents, void *userdata) {
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+static int mount_process_proc_self_mountinfo(Manager *m) {
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_cleanup_set_free_ Set *around = NULL, *gone = NULL;
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- Manager *m = userdata;
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const char *what;
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Iterator i;
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Unit *u;
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int r;
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assert(m);
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- assert(revents & EPOLLIN);
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r = drain_libmount(m);
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if (r <= 0)
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@@ -1898,6 +1913,15 @@ static int mount_dispatch_io(sd_event_source *source, int fd, uint32_t revents,
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return 0;
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}
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+static int mount_dispatch_io(sd_event_source *source, int fd, uint32_t revents, void *userdata) {
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+ Manager *m = userdata;
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+
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+ assert(m);
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+ assert(revents & EPOLLIN);
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+
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+ return mount_process_proc_self_mountinfo(m);
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+}
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+
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static void mount_reset_failed(Unit *u) {
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Mount *m = MOUNT(u);
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