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Commit b2b80195 authored by Al Viro's avatar Al Viro
Browse files

dealing with the rest of shrink_dentry_list() livelock 



We have the same problem with ->d_lock order in the inner loop, where
we are dropping references to ancestors.  Same solution, basically -
instead of using dentry_kill() we use lock_parent() (introduced in the
previous commit) to get that lock in a safe way, recheck ->d_count
(in case if lock_parent() has ended up dropping and retaking ->d_lock
and somebody managed to grab a reference during that window), trylock
the inode->i_lock and use __dentry_kill() to do the rest.

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 046b961b

fs/dcache.c

+20 −2
Original line number Diff line number Diff line
@@ -885,8 +885,26 @@ static void shrink_dentry_list(struct list_head *list) 
		 * fragmentation.

		 */

		dentry = parent;

		while (dentry && !lockref_put_or_lock(&dentry->d_lockref))

			dentry = dentry_kill(dentry, 1);

		while (dentry && !lockref_put_or_lock(&dentry->d_lockref)) {

			parent = lock_parent(dentry);

			if (dentry->d_lockref.count != 1) {

				dentry->d_lockref.count--;

				spin_unlock(&dentry->d_lock);

				if (parent)

					spin_unlock(&parent->d_lock);

				break;

			}

			inode = dentry->d_inode;	/* can't be NULL */

			if (unlikely(!spin_trylock(&inode->i_lock))) {

				spin_unlock(&dentry->d_lock);

				if (parent)

					spin_unlock(&parent->d_lock);

				cpu_relax();

				continue;

			}

			__dentry_kill(dentry);

			dentry = parent;

		}

	}

}