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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>
This commit is contained in:
Al Viro 2016-07-03 23:15:21 -04:00
parent 1a695a905c
commit 2864f30142
1 changed files with 34 additions and 7 deletions
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41
fs/inode.c
View File

@ -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);