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Shift rcu_read_{,un}lock() inside fast_dput()

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Shrink rcu_read_lock() scopes surrounding fast_dput() calls.
Both callers are immediately preceded and followed by
rcu_read_lock()/rcu_read_unlock() resp.  Shrink that down
into fast_dput() itself; in case when fast_dput() ends up
grabbing ->d_lock, we can pull rcu_read_unlock() up to
right after spin_lock().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2026-04-11 03:56:42 -04:00
parent 0954b4b558
commit b4143e0e71
1 changed files with 14 additions and 16 deletions
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30
fs/dcache.c
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@ -885,17 +885,17 @@ EXPORT_SYMBOL(d_mark_dontcache);
* If unsuccessful, we return false, having already taken the dentry lock.
* In that case refcount is guaranteed to be zero and we have already
* decided that it's not worth keeping around.
*
* The caller needs to hold the RCU read lock, so that the dentry is
* guaranteed to stay around even if the refcount goes down to zero!
*/
static inline bool fast_dput(struct dentry *dentry)
{
int ret;
/*
* try to decrement the lockref optimistically.
* Try to decrement the lockref optimistically.
* RCU read lock held so that dentry is guaranteed to stay around
* even if the refcount goes down to zero.
*/
rcu_read_lock();
ret = lockref_put_return(&dentry->d_lockref);
/*
@ -905,6 +905,7 @@ static inline bool fast_dput(struct dentry *dentry)
*/
if (unlikely(ret < 0)) {
spin_lock(&dentry->d_lock);
rcu_read_unlock();
if (WARN_ON_ONCE(dentry->d_lockref.count <= 0)) {
spin_unlock(&dentry->d_lock);
return true;
@ -916,8 +917,10 @@ static inline bool fast_dput(struct dentry *dentry)
/*
* If we weren't the last ref, we're done.
*/
if (ret)
if (ret) {
rcu_read_unlock();
return true;
}
/*
* Can we decide that decrement of refcount is all we needed without
@ -925,8 +928,10 @@ static inline bool fast_dput(struct dentry *dentry)
* dentry looks like it ought to be retained and there's nothing else
* to do.
*/
if (retain_dentry(dentry, false))
if (retain_dentry(dentry, false)) {
rcu_read_unlock();
return true;
}
/*
* Either not worth retaining or we can't tell without the lock.
@ -934,6 +939,7 @@ static inline bool fast_dput(struct dentry *dentry)
* but we'll need to re-check the situation after getting the lock.
*/
spin_lock(&dentry->d_lock);
rcu_read_unlock();
/*
* Did somebody else grab a reference to it in the meantime, and
@ -991,12 +997,8 @@ void dput(struct dentry *dentry)
if (!dentry)
return;
might_sleep();
rcu_read_lock();
if (likely(fast_dput(dentry))) {
rcu_read_unlock();
if (likely(fast_dput(dentry)))
return;
}
rcu_read_unlock();
finish_dput(dentry);
}
EXPORT_SYMBOL(dput);
@ -1044,12 +1046,8 @@ EXPORT_SYMBOL(__move_to_shrink_list);
void dput_to_list(struct dentry *dentry, struct list_head *list)
{
rcu_read_lock();
if (likely(fast_dput(dentry))) {
rcu_read_unlock();
if (likely(fast_dput(dentry)))
return;
}
rcu_read_unlock();
__move_to_shrink_list(dentry, list);
spin_unlock(&dentry->d_lock);
}