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Merge branch 'for-linus-2' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs
Pull vfs dcache livelock fix from Al Viro: "Fixes for livelocks in shrink_dentry_list() introduced by fixes to shrink list corruption; the root cause was that trylock of parent's ->d_lock could be disrupted by d_walk() happening on other CPUs, resulting in shrink_dentry_list() making no progress *and* the same d_walk() being called again and again for as long as shrink_dentry_list() doesn't get past that mess. The solution is to have shrink_dentry_list() treat that trylock failure not as 'try to do the same thing again', but 'lock them in the right order'" * 'for-linus-2' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: dentry_kill() doesn't need the second argument now dealing with the rest of shrink_dentry_list() livelock shrink_dentry_list(): take parent's ->d_lock earlier expand dentry_kill(dentry, 0) in shrink_dentry_list() split dentry_kill() lift the "already marked killed" case into shrink_dentry_list()
This commit is contained in:
Linus Torvalds
commit
6f6111e4a7
155
fs/dcache.c
155
fs/dcache.c
@ -441,42 +441,12 @@ void d_drop(struct dentry *dentry)
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}
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EXPORT_SYMBOL(d_drop);
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/*
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* Finish off a dentry we've decided to kill.
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* dentry->d_lock must be held, returns with it unlocked.
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* If ref is non-zero, then decrement the refcount too.
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* Returns dentry requiring refcount drop, or NULL if we're done.
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*/
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static struct dentry *
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dentry_kill(struct dentry *dentry, int unlock_on_failure)
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__releases(dentry->d_lock)
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static void __dentry_kill(struct dentry *dentry)
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{
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struct inode *inode;
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struct dentry *parent = NULL;
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bool can_free = true;
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if (unlikely(dentry->d_flags & DCACHE_DENTRY_KILLED)) {
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can_free = dentry->d_flags & DCACHE_MAY_FREE;
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spin_unlock(&dentry->d_lock);
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goto out;
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}
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inode = dentry->d_inode;
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if (inode && !spin_trylock(&inode->i_lock)) {
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relock:
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if (unlock_on_failure) {
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spin_unlock(&dentry->d_lock);
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cpu_relax();
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}
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return dentry; /* try again with same dentry */
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}
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if (!IS_ROOT(dentry))
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parent = dentry->d_parent;
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if (parent && !spin_trylock(&parent->d_lock)) {
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if (inode)
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spin_unlock(&inode->i_lock);
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goto relock;
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}
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/*
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* The dentry is now unrecoverably dead to the world.
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@ -520,9 +490,72 @@ relock:
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can_free = false;
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}
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spin_unlock(&dentry->d_lock);
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out:
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if (likely(can_free))
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dentry_free(dentry);
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}
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/*
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* Finish off a dentry we've decided to kill.
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* dentry->d_lock must be held, returns with it unlocked.
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* If ref is non-zero, then decrement the refcount too.
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* Returns dentry requiring refcount drop, or NULL if we're done.
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*/
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static struct dentry *dentry_kill(struct dentry *dentry)
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__releases(dentry->d_lock)
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{
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struct inode *inode = dentry->d_inode;
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struct dentry *parent = NULL;
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if (inode && unlikely(!spin_trylock(&inode->i_lock)))
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goto failed;
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if (!IS_ROOT(dentry)) {
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parent = dentry->d_parent;
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if (unlikely(!spin_trylock(&parent->d_lock))) {
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if (inode)
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spin_unlock(&inode->i_lock);
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goto failed;
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}
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}
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__dentry_kill(dentry);
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return parent;
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failed:
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spin_unlock(&dentry->d_lock);
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cpu_relax();
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return dentry; /* try again with same dentry */
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}
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static inline struct dentry *lock_parent(struct dentry *dentry)
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{
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struct dentry *parent = dentry->d_parent;
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if (IS_ROOT(dentry))
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return NULL;
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if (likely(spin_trylock(&parent->d_lock)))
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return parent;
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spin_unlock(&dentry->d_lock);
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rcu_read_lock();
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again:
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parent = ACCESS_ONCE(dentry->d_parent);
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spin_lock(&parent->d_lock);
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/*
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* We can't blindly lock dentry until we are sure
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* that we won't violate the locking order.
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* Any changes of dentry->d_parent must have
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* been done with parent->d_lock held, so
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* spin_lock() above is enough of a barrier
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* for checking if it's still our child.
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*/
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if (unlikely(parent != dentry->d_parent)) {
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spin_unlock(&parent->d_lock);
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goto again;
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}
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rcu_read_unlock();
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if (parent != dentry)
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spin_lock(&dentry->d_lock);
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else
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parent = NULL;
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return parent;
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}
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@ -579,7 +612,7 @@ repeat:
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return;
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kill_it:
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dentry = dentry_kill(dentry, 1);
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dentry = dentry_kill(dentry);
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if (dentry)
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goto repeat;
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}
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@ -797,8 +830,11 @@ static void shrink_dentry_list(struct list_head *list)
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struct dentry *dentry, *parent;
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while (!list_empty(list)) {
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struct inode *inode;
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dentry = list_entry(list->prev, struct dentry, d_lru);
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spin_lock(&dentry->d_lock);
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parent = lock_parent(dentry);
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/*
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* The dispose list is isolated and dentries are not accounted
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* to the LRU here, so we can simply remove it from the list
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@ -812,26 +848,33 @@ static void shrink_dentry_list(struct list_head *list)
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*/
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if ((int)dentry->d_lockref.count > 0) {
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spin_unlock(&dentry->d_lock);
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if (parent)
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spin_unlock(&parent->d_lock);
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continue;
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}
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parent = dentry_kill(dentry, 0);
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/*
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* If dentry_kill returns NULL, we have nothing more to do.
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*/
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if (!parent)
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continue;
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if (unlikely(parent == dentry)) {
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/*
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* trylocks have failed and d_lock has been held the
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* whole time, so it could not have been added to any
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* other lists. Just add it back to the shrink list.
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*/
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if (unlikely(dentry->d_flags & DCACHE_DENTRY_KILLED)) {
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bool can_free = dentry->d_flags & DCACHE_MAY_FREE;
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spin_unlock(&dentry->d_lock);
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if (parent)
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spin_unlock(&parent->d_lock);
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if (can_free)
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dentry_free(dentry);
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continue;
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}
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inode = dentry->d_inode;
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if (inode && unlikely(!spin_trylock(&inode->i_lock))) {
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d_shrink_add(dentry, list);
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spin_unlock(&dentry->d_lock);
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if (parent)
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spin_unlock(&parent->d_lock);
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continue;
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}
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__dentry_kill(dentry);
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/*
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* We need to prune ancestors too. This is necessary to prevent
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* quadratic behavior of shrink_dcache_parent(), but is also
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@ -839,8 +882,26 @@ static void shrink_dentry_list(struct list_head *list)
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* fragmentation.
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*/
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dentry = parent;
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while (dentry && !lockref_put_or_lock(&dentry->d_lockref))
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dentry = dentry_kill(dentry, 1);
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while (dentry && !lockref_put_or_lock(&dentry->d_lockref)) {
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parent = lock_parent(dentry);
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if (dentry->d_lockref.count != 1) {
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dentry->d_lockref.count--;
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spin_unlock(&dentry->d_lock);
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if (parent)
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spin_unlock(&parent->d_lock);
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break;
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}
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inode = dentry->d_inode; /* can't be NULL */
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if (unlikely(!spin_trylock(&inode->i_lock))) {
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spin_unlock(&dentry->d_lock);
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if (parent)
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spin_unlock(&parent->d_lock);
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cpu_relax();
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continue;
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}
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__dentry_kill(dentry);
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dentry = parent;
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}
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}
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}
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