From 2864f301424227d9d3bde6d550bc224a83535b46 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Sun, 3 Jul 2016 23:15:21 -0400 Subject: [PATCH] iget_locked et.al.: make sure we don't return bad inodes If one thread does iget_locked(), proceeds to try and set the new inode up and fails, inode will be unhashed and dropped. However, another thread doing ilookup/iget_locked in the middle of that would end up finding a half-set-up inode, grabbing a reference, waiting for it to come unlocked and getting the resulting bad inode. It's a race (if that ilookup had been called just after the failure of setup attempt it wouldn't have found the sucker at all), particularly unpleasant in cases when failure is transient/caller-dependent/etc. While it can be dealt with in the callers, there's no reason not to handle it in fs/inode.c primitives, especially since the cost is trivial. Signed-off-by: Al Viro --- fs/inode.c | 41 ++++++++++++++++++++++++++++++++++------- 1 file changed, 34 insertions(+), 7 deletions(-) diff --git a/fs/inode.c b/fs/inode.c index 4ccbc21b30ce..d123fe4b6f7d 100644 --- a/fs/inode.c +++ b/fs/inode.c @@ -1019,13 +1019,17 @@ struct inode *iget5_locked(struct super_block *sb, unsigned long hashval, { struct hlist_head *head = inode_hashtable + hash(sb, hashval); struct inode *inode; - +again: spin_lock(&inode_hash_lock); inode = find_inode(sb, head, test, data); spin_unlock(&inode_hash_lock); if (inode) { wait_on_inode(inode); + if (unlikely(inode_unhashed(inode))) { + iput(inode); + goto again; + } return inode; } @@ -1062,6 +1066,10 @@ struct inode *iget5_locked(struct super_block *sb, unsigned long hashval, destroy_inode(inode); inode = old; wait_on_inode(inode); + if (unlikely(inode_unhashed(inode))) { + iput(inode); + goto again; + } } return inode; @@ -1089,12 +1097,16 @@ struct inode *iget_locked(struct super_block *sb, unsigned long ino) { struct hlist_head *head = inode_hashtable + hash(sb, ino); struct inode *inode; - +again: spin_lock(&inode_hash_lock); inode = find_inode_fast(sb, head, ino); spin_unlock(&inode_hash_lock); if (inode) { wait_on_inode(inode); + if (unlikely(inode_unhashed(inode))) { + iput(inode); + goto again; + } return inode; } @@ -1129,6 +1141,10 @@ struct inode *iget_locked(struct super_block *sb, unsigned long ino) destroy_inode(inode); inode = old; wait_on_inode(inode); + if (unlikely(inode_unhashed(inode))) { + iput(inode); + goto again; + } } return inode; } @@ -1264,10 +1280,16 @@ EXPORT_SYMBOL(ilookup5_nowait); struct inode *ilookup5(struct super_block *sb, unsigned long hashval, int (*test)(struct inode *, void *), void *data) { - struct inode *inode = ilookup5_nowait(sb, hashval, test, data); - - if (inode) + struct inode *inode; +again: + inode = ilookup5_nowait(sb, hashval, test, data); + if (inode) { wait_on_inode(inode); + if (unlikely(inode_unhashed(inode))) { + iput(inode); + goto again; + } + } return inode; } EXPORT_SYMBOL(ilookup5); @@ -1284,13 +1306,18 @@ struct inode *ilookup(struct super_block *sb, unsigned long ino) { struct hlist_head *head = inode_hashtable + hash(sb, ino); struct inode *inode; - +again: spin_lock(&inode_hash_lock); inode = find_inode_fast(sb, head, ino); spin_unlock(&inode_hash_lock); - if (inode) + if (inode) { wait_on_inode(inode); + if (unlikely(inode_unhashed(inode))) { + iput(inode); + goto again; + } + } return inode; } EXPORT_SYMBOL(ilookup);