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 dbad7c993053
("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: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/super.c b/fs/super.c
index 47d11e0..c183835 100644 (file)
--- a/fs/super.c
+++ b/fs/super.c
@@ -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.
-        */
-       percpu_rwsem_release(sb->s_writers.rw_sem + level-1, 0, _THIS_IP_);
 }
 
-static void sb_freeze_unlock(struct super_block *sb)
+/*
+ * We are going to return to userspace and forget about these locks, the
+ * ownership goes to the caller of thaw_super() which does unlock().
+ */
+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_);
+}
+
+/*
+ * 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;
                }