Re: [RFC][PATCH] PM / Freezer: Freeze filesystems along with freezing processes (was: Re: PM / hibernate xfs lock up / xfs_reclaim_inodes_ag)

Hi!

Freeze all filesystems during the freezing of tasks by calling
freeze_bdev() for each of them and thaw them during the thawing
of tasks with the help of thaw_bdev().

This is needed by hibernation, because some filesystems (e.g. XFS)
deadlock with the preallocation of memory used by it if the memory
pressure caused by it is too heavy.

The additional benefit of this change is that, if something goes
wrong after filesystems have been frozen, they will stay in a
consistent state and journal replays won't be necessary (e.g. after
a failing suspend or resume).  In particular, this should help to
solve a long-standing issue that in some cases during resume from
hibernation the boot loader causes the journal to be replied for the
filesystem containing the kernel image and initrd causing it to
become inconsistent with the information stored in the hibernation
image.

+/**
+ * freeze_filesystems - Force all filesystems into a consistent state.
+ */
+void freeze_filesystems(void)
+{
+	struct super_block *sb;
+
+	lockdep_off();

Ouch. So... why do we need to silence this?

+	/*
+	 * Freeze in reverse order so filesystems dependant upon others are
+	 * frozen in the right order (eg. loopback on ext3).
+	 */
+	list_for_each_entry_reverse(sb, &super_blocks, s_list) {
+		if (!sb->s_root || !sb->s_bdev ||
+		    (sb->s_frozen == SB_FREEZE_TRANS) ||
+		    (sb->s_flags & MS_RDONLY) ||
+		    (sb->s_flags & MS_FROZEN))
+			continue;

Should we stop NFS from modifying remote server, too?

Plus... ext3 writes to read-only filesystems on mount; not sure if it
does it later. But RDONLY means 'user cant write to it' not 'bdev will
not be modified'. Should we freeze all?

How can 'already frozen' happen?

+	list_for_each_entry(sb, &super_blocks, s_list)
+		if (sb->s_flags & MS_FROZEN) {
+			sb->s_flags &= ~MS_FROZEN;
+			thaw_bdev(sb->s_bdev, sb);
+		}

...because we'll unfreeze it even if we did not freeze it...

									Pavel
-- 
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