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 <viro@zeniv.linux.org.uk>
diff --git a/fs/inode.c b/fs/inode.c
index 4ccbc21..d123fe4 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1019,13 +1019,17 @@
{
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 @@
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 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 @@
destroy_inode(inode);
inode = old;
wait_on_inode(inode);
+ if (unlikely(inode_unhashed(inode))) {
+ iput(inode);
+ goto again;
+ }
}
return inode;
}
@@ -1264,10 +1280,16 @@
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 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);