[patch 55/61] lock validator: special locking: sb->s_umount

[Ingo Molnar]

From: Ingo Molnar <mingo@xxxxxxx>

workaround for special sb->s_umount locking rule.

s_umount gets held across a series of lock dropping and releasing
in prune_one_dentry(), so i changed the order, at the risk of
introducing a umount race. FIXME.

i think a better fix would be to do the unlocks as _non_nested in
prune_one_dentry(), and to do the up_read() here as
an up_read_non_nested() as well?

Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Arjan van de Ven <arjan@xxxxxxxxxxxxxxx>
---
 fs/dcache.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Index: linux/fs/dcache.c
===================================================================
--- linux.orig/fs/dcache.c
+++ linux/fs/dcache.c
@@ -470,8 +470,9 @@ static void prune_dcache(int count, stru
 		s_umount = &dentry->d_sb->s_umount;
 		if (down_read_trylock(s_umount)) {
 			if (dentry->d_sb->s_root != NULL) {
-				prune_one_dentry(dentry);
+// lockdep hack: do this better!
 				up_read(s_umount);
+				prune_one_dentry(dentry);
 				continue;
 			}
 			up_read(s_umount);
-
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