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fast_dput(): having ->d_delete() is not reason to delay refcount decrement

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->d_delete() is a way for filesystem to tell that dentry is not worth
keeping cached.  It is not guaranteed to be called every time a dentry
has refcount drop down to zero; it is not guaranteed to be called before
dentry gets evicted.  In other words, it is not suitable for any kind
of keeping track of dentry state.

None of the in-tree filesystems attempt to use it that way, fortunately.

So the contortions done by fast_dput() (as well as dentry_kill()) are
not warranted.  fast_dput() certainly should treat having ->d_delete()
instance as "can't assume we'll be keeping it", but that's not different
from the way we treat e.g. DCACHE_DONTCACHE (which is rather similar
to making ->d_delete() returns true when called).

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2023-10-30 00:02:14 -04:00
parent cd9f84f35c
commit 15220fbf18
1 changed files with 2 additions and 10 deletions
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12
fs/dcache.c
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@ -768,15 +768,7 @@ static inline bool fast_dput(struct dentry *dentry)
unsigned int d_flags;
/*
* If we have a d_op->d_delete() operation, we sould not
* let the dentry count go to zero, so use "put_or_lock".
*/
if (unlikely(dentry->d_flags & DCACHE_OP_DELETE))
return lockref_put_or_lock(&dentry->d_lockref);
/*
* .. otherwise, we can try to just decrement the
* lockref optimistically.
* try to decrement the lockref optimistically.
*/
ret = lockref_put_return(&dentry->d_lockref);
@ -830,7 +822,7 @@ static inline bool fast_dput(struct dentry *dentry)
*/
smp_rmb();
d_flags = READ_ONCE(dentry->d_flags);
d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST |
d_flags &= DCACHE_REFERENCED | DCACHE_LRU_LIST | DCACHE_OP_DELETE |
DCACHE_DISCONNECTED | DCACHE_DONTCACHE;
/* Nothing to do? Dropping the reference was all we needed? */