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fs: distinguish between user initiated freeze and kernel initiated freeze

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Userspace can freeze a filesystem using the FIFREEZE ioctl or by
suspending the block device; this state persists until userspace thaws
the filesystem with the FITHAW ioctl or resuming the block device.
Since commit 18e9e5104f ("Introduce freeze_super and thaw_super for
the fsfreeze ioctl") we only allow the first freeze command to succeed.

The kernel may decide that it is necessary to freeze a filesystem for
its own internal purposes, such as suspends in progress, filesystem fsck
activities, or quiescing a device prior to removal.  Userspace thaw
commands must never break a kernel freeze, and kernel thaw commands
shouldn't undo userspace's freeze command.

Introduce a couple of freeze holder flags and wire it into the
sb_writers state.  One kernel and one userspace freeze are allowed to
coexist at the same time; the filesystem will not thaw until both are
lifted.

I wonder if the f2fs/gfs2 code should be using a kernel freeze here, but
for now we'll use FREEZE_HOLDER_USERSPACE to preserve existing
behaviors.

Cc: mcgrof@kernel.org
Cc: jack@suse.cz
Cc: hch@infradead.org
Cc: ruansy.fnst@fujitsu.com
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
This commit is contained in:
Darrick J. Wong
2023-07-17 09:00:09 -07:00
parent fdf0eaf114
commit 880b957785
8 changed files with 106 additions and 34 deletions
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8
block/bdev.c
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@@ -248,9 +248,9 @@ int freeze_bdev(struct block_device *bdev)
if (!sb)
goto sync;
if (sb->s_op->freeze_super)
error = sb->s_op->freeze_super(sb);
error = sb->s_op->freeze_super(sb, FREEZE_HOLDER_USERSPACE);
else
error = freeze_super(sb);
error = freeze_super(sb, FREEZE_HOLDER_USERSPACE);
deactivate_super(sb);
if (error) {
@@ -291,9 +291,9 @@ int thaw_bdev(struct block_device *bdev)
goto out;
if (sb->s_op->thaw_super)
error = sb->s_op->thaw_super(sb);
error = sb->s_op->thaw_super(sb, FREEZE_HOLDER_USERSPACE);
else
error = thaw_super(sb);
error = thaw_super(sb, FREEZE_HOLDER_USERSPACE);
if (error)
bdev->bd_fsfreeze_count++;
else