From: Miklos Szeredi <mszeredi@xxxxxxx>
IBM reported a deadlock in select_parent(). This was found to be caused by
taking rename_lock when already locked when restarting the tree traversal.
There are two cases when the traversal needs to be restarted:
1) concurrent d_move(); this can only happen when not already locked,
since taking rename_lock protects against concurrent d_move().
2) racing with final d_put() on child just at the moment of ascending
to parent; rename_lock doesn't protect against this rare race, so it
can happen when already locked.
Because of case 2. we need to be able to handle restarting the traversal
when rename_lock is already held. This patch fixes all three callers of
try_to_ascend().
IBM reported that the deadlock is gone with this patch. However, there's still
a soft lockup which is addressed by the next patch.
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
fs/dcache.c | 19 +++++++++++++------
1 file changed, 13 insertions(+), 6 deletions(-)
Index: linux-2.6/fs/dcache.c
===================================================================
--- linux-2.6.orig/fs/dcache.c 2012-09-17 19:56:19.000000000 +0200
+++ linux-2.6/fs/dcache.c 2012-09-17 20:04:07.000000000 +0200
@@ -1134,8 +1134,10 @@ int have_submounts(struct dentry *parent
return 1;
rename_retry:
- locked = 1;
- write_seqlock(&rename_lock);
+ if (!locked) {
+ locked = 1;
+ write_seqlock(&rename_lock);
+ }
goto again;
}
EXPORT_SYMBOL(have_submounts);
@@ -1236,8 +1238,10 @@ static int select_parent(struct dentry *
rename_retry:
if (found)
return found;
- locked = 1;
- write_seqlock(&rename_lock);
+ if (!locked) {
+ locked = 1;
+ write_seqlock(&rename_lock);
+ }
goto again;
}
@@ -3035,8 +3039,11 @@ void d_genocide(struct dentry *root)
return;
rename_retry:
- locked = 1;
- write_seqlock(&rename_lock);
+ if (!locked) {
+ locked = 1;
+ write_seqlock(&rename_lock);
+
+ }
goto again;
}
--
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