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deal with deadlock in d_walk()

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... by not hitting rename_retry for reasons other than rename having
happened.  In other words, do _not_ restart when finding that
between unlocking the child and locking the parent the former got
into __dentry_kill().  Skip the killed siblings instead...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2014-10-26 19:31:10 -04:00
parent 946e51f2bf
commit ca5358ef75
1 changed files with 16 additions and 15 deletions
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31
fs/dcache.c
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@ -495,7 +495,7 @@ static void __dentry_kill(struct dentry *dentry)
}
/* if it was on the hash then remove it */
__d_drop(dentry);
list_del(&dentry->d_child);
__list_del_entry(&dentry->d_child);
/*
* Inform d_walk() that we are no longer attached to the
* dentry tree
@ -1081,33 +1081,31 @@ resume:
/*
* All done at this level ... ascend and resume the search.
*/
rcu_read_lock();
ascend:
if (this_parent != parent) {
struct dentry *child = this_parent;
this_parent = child->d_parent;
rcu_read_lock();
spin_unlock(&child->d_lock);
spin_lock(&this_parent->d_lock);
/*
* might go back up the wrong parent if we have had a rename
* or deletion
*/
if (this_parent != child->d_parent ||
(child->d_flags & DCACHE_DENTRY_KILLED) ||
need_seqretry(&rename_lock, seq)) {
spin_unlock(&this_parent->d_lock);
rcu_read_unlock();
/* might go back up the wrong parent if we have had a rename. */
if (need_seqretry(&rename_lock, seq))
goto rename_retry;
next = child->d_child.next;
while (unlikely(child->d_flags & DCACHE_DENTRY_KILLED)) {
if (next == &this_parent->d_subdirs)
goto ascend;
child = list_entry(next, struct dentry, d_child);
next = next->next;
}
rcu_read_unlock();
next = child->d_child.next;
goto resume;
}
if (need_seqretry(&rename_lock, seq)) {
spin_unlock(&this_parent->d_lock);
if (need_seqretry(&rename_lock, seq))
goto rename_retry;
}
rcu_read_unlock();
if (finish)
finish(data);
@ -1117,6 +1115,9 @@ out_unlock:
return;
rename_retry:
spin_unlock(&this_parent->d_lock);
rcu_read_unlock();
BUG_ON(seq & 1);
if (!retry)
return;
seq = 1;