Commit f1a96220 authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Al Viro
Browse files

fs/super.c: don't fool lockdep in freeze_super() and thaw_super() paths 



sb_wait_write()->percpu_rwsem_release() fools lockdep to avoid the
false-positives. Now that xfs was fixed by Dave's commit dbad7c99
("xfs: stop holding ILOCK over filldir callbacks") we can remove it and
change freeze_super() and thaw_super() to run with s_writers.rw_sem locks
held; we add two trivial helpers for that, lockdep_sb_freeze_release()
and lockdep_sb_freeze_acquire().

xfstests-dev/check `grep -il freeze tests/*/???` does not trigger any
warning from lockdep.

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 89f39af1

fs/super.c

+25 −12
Original line number Diff line number Diff line
@@ -1269,25 +1269,34 @@ EXPORT_SYMBOL(__sb_start_write); 
static void sb_wait_write(struct super_block *sb, int level)

{

	percpu_down_write(sb->s_writers.rw_sem + level-1);

}



/*

	 * We are going to return to userspace and forget about this lock, the

	 * ownership goes to the caller of thaw_super() which does unlock.

	 *

	 * FIXME: we should do this before return from freeze_super() after we

	 * called sync_filesystem(sb) and s_op->freeze_fs(sb), and thaw_super()

	 * should re-acquire these locks before s_op->unfreeze_fs(sb). However

	 * this leads to lockdep false-positives, so currently we do the early

	 * release right after acquire.

 * We are going to return to userspace and forget about these locks, the

 * ownership goes to the caller of thaw_super() which does unlock().

 */

	percpu_rwsem_release(sb->s_writers.rw_sem + level-1, 0, _THIS_IP_);

static void lockdep_sb_freeze_release(struct super_block *sb)

{

	int level;



	for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)

		percpu_rwsem_release(sb->s_writers.rw_sem + level, 0, _THIS_IP_);

}



static void sb_freeze_unlock(struct super_block *sb)

/*

 * Tell lockdep we are holding these locks before we call ->unfreeze_fs(sb).

 */

static void lockdep_sb_freeze_acquire(struct super_block *sb)

{

	int level;



	for (level = 0; level < SB_FREEZE_LEVELS; ++level)

		percpu_rwsem_acquire(sb->s_writers.rw_sem + level, 0, _THIS_IP_);

}



static void sb_freeze_unlock(struct super_block *sb)

{

	int level;



	for (level = SB_FREEZE_LEVELS - 1; level >= 0; level--)

		percpu_up_write(sb->s_writers.rw_sem + level);
@@ -1383,6 +1392,7 @@ int freeze_super(struct super_block *sb) 
	 * when frozen is set to SB_FREEZE_COMPLETE, and for thaw_super().

	 */

	sb->s_writers.frozen = SB_FREEZE_COMPLETE;

	lockdep_sb_freeze_release(sb);

	up_write(&sb->s_umount);

	return 0;

}
@@ -1409,11 +1419,14 @@ int thaw_super(struct super_block *sb) 
		goto out;

	}



	lockdep_sb_freeze_acquire(sb);



	if (sb->s_op->unfreeze_fs) {

		error = sb->s_op->unfreeze_fs(sb);

		if (error) {

			printk(KERN_ERR

				"VFS:Filesystem thaw failed\n");

			lockdep_sb_freeze_release(sb);

			up_write(&sb->s_umount);

			return error;

		}

CRA Git | Maintained and supported by SUSTech CRA and CCSE