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deal with deadlock in d_walk()

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commit ca5358ef75fc69fee5322a38a340f5739d997c10 upstream.

... 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>
[bwh: Backported to 3.2:
 - As we only have try_to_ascend() and not d_walk(), apply this
   change to all callers of try_to_ascend()
 - Adjust context to make __dentry_kill() apply to d_kill()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
[lizf: Backported to 3.4: fold the fix 2d5a2e6775fa in 3.2.y into this patch]
Signed-off-by: Zefan Li <lizefan@huawei.com>
This commit is contained in:
Al Viro 2014-10-26 19:31:10 -04:00 committed by Zefan Li
parent 6fd17def6d
commit a91da0b39a
1 changed files with 65 additions and 40 deletions
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105
fs/dcache.c
View file

@ -368,9 +368,9 @@ static struct dentry *d_kill(struct dentry *dentry, struct dentry *parent)
__releases(parent->d_lock)
__releases(dentry->d_inode->i_lock)
{
list_del(&dentry->d_child);
__list_del_entry(&dentry->d_child);
/*
* Inform try_to_ascend() that we are no longer attached to the
* Inform ascending readers that we are no longer attached to the
* dentry tree
*/
dentry->d_flags |= DCACHE_DENTRY_KILLED;
@ -1011,34 +1011,6 @@ void shrink_dcache_for_umount(struct super_block *sb)
}
}
/*
* This tries to ascend one level of parenthood, but
* we can race with renaming, so we need to re-check
* the parenthood after dropping the lock and check
* that the sequence number still matches.
*/
static struct dentry *try_to_ascend(struct dentry *old, int locked, unsigned seq)
{
struct dentry *new = old->d_parent;
rcu_read_lock();
spin_unlock(&old->d_lock);
spin_lock(&new->d_lock);
/*
* might go back up the wrong parent if we have had a rename
* or deletion
*/
if (new != old->d_parent ||
(old->d_flags & DCACHE_DENTRY_KILLED) ||
(!locked && read_seqretry(&rename_lock, seq))) {
spin_unlock(&new->d_lock);
new = NULL;
}
rcu_read_unlock();
return new;
}
/*
* Search for at least 1 mount point in the dentry's subdirs.
@ -1094,30 +1066,48 @@ 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 = try_to_ascend(this_parent, locked, seq);
if (!this_parent)
this_parent = child->d_parent;
spin_unlock(&child->d_lock);
spin_lock(&this_parent->d_lock);
/* might go back up the wrong parent if we have had a rename */
if (!locked && read_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();
goto resume;
}
spin_unlock(&this_parent->d_lock);
if (!locked && read_seqretry(&rename_lock, seq))
goto rename_retry;
spin_unlock(&this_parent->d_lock);
rcu_read_unlock();
if (locked)
write_sequnlock(&rename_lock);
return 0; /* No mount points found in tree */
positive:
if (!locked && read_seqretry(&rename_lock, seq))
goto rename_retry;
goto rename_retry_unlocked;
if (locked)
write_sequnlock(&rename_lock);
return 1;
rename_retry:
spin_unlock(&this_parent->d_lock);
rcu_read_unlock();
if (locked)
goto again;
rename_retry_unlocked:
locked = 1;
write_seqlock(&rename_lock);
goto again;
@ -1182,6 +1172,7 @@ resume:
*/
if (found && need_resched()) {
spin_unlock(&dentry->d_lock);
rcu_read_lock();
goto out;
}
@ -1201,23 +1192,40 @@ 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 = try_to_ascend(this_parent, locked, seq);
if (!this_parent)
this_parent = child->d_parent;
spin_unlock(&child->d_lock);
spin_lock(&this_parent->d_lock);
/* might go back up the wrong parent if we have had a rename */
if (!locked && read_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();
goto resume;
}
out:
spin_unlock(&this_parent->d_lock);
if (!locked && read_seqretry(&rename_lock, seq))
goto rename_retry;
spin_unlock(&this_parent->d_lock);
rcu_read_unlock();
if (locked)
write_sequnlock(&rename_lock);
return found;
rename_retry:
spin_unlock(&this_parent->d_lock);
rcu_read_unlock();
if (found)
return found;
if (locked)
@ -2955,26 +2963,43 @@ resume:
}
spin_unlock(&dentry->d_lock);
}
rcu_read_lock();
ascend:
if (this_parent != root) {
struct dentry *child = this_parent;
if (!(this_parent->d_flags & DCACHE_GENOCIDE)) {
this_parent->d_flags |= DCACHE_GENOCIDE;
this_parent->d_count--;
}
this_parent = try_to_ascend(this_parent, locked, seq);
if (!this_parent)
this_parent = child->d_parent;
spin_unlock(&child->d_lock);
spin_lock(&this_parent->d_lock);
/* might go back up the wrong parent if we have had a rename */
if (!locked && read_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();
goto resume;
}
spin_unlock(&this_parent->d_lock);
if (!locked && read_seqretry(&rename_lock, seq))
goto rename_retry;
spin_unlock(&this_parent->d_lock);
rcu_read_unlock();
if (locked)
write_sequnlock(&rename_lock);
return;
rename_retry:
spin_unlock(&this_parent->d_lock);
rcu_read_unlock();
if (locked)
goto again;
locked = 1;