Commit c72e0575 authored by Frederic Weisbecker's avatar Frederic Weisbecker
Browse files

kill-the-bkl/reiserfs: acquire the inode mutex safely 



While searching a pathname, an inode mutex can be acquired
in do_lookup() which calls reiserfs_lookup() which in turn
acquires the write lock.

On the other side reiserfs_fill_super() can acquire the write_lock
and then call reiserfs_lookup_privroot() which can acquire an
inode mutex (the root of the mount point).

So we theoretically risk an AB - BA lock inversion that could lead
to a deadlock.

As for other lock dependencies found since the bkl to mutex
conversion, the fix is to use reiserfs_mutex_lock_safe() which
drops the lock dependency to the write lock.

[ Impact: fix a possible deadlock with reiserfs ]

Cc: Jeff Mahoney <jeffm@suse.com>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Alexander Beregalov <a.beregalov@gmail.com>
Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
parent 2ac62695

fs/reiserfs/journal.c

+0 −34
Original line number Diff line number Diff line
@@ -537,40 +537,6 @@ static inline void insert_journal_hash(struct reiserfs_journal_cnode **table, 
	journal_hash(table, cn->sb, cn->blocknr) = cn;

}



/*

 * Several mutexes depend on the write lock.

 * However sometimes we want to relax the write lock while we hold

 * these mutexes, according to the release/reacquire on schedule()

 * properties of the Bkl that were used.

 * Reiserfs performances and locking were based on this scheme.

 * Now that the write lock is a mutex and not the bkl anymore, doing so

 * may result in a deadlock:

 *

 * A acquire write_lock

 * A acquire j_commit_mutex

 * A release write_lock and wait for something

 * B acquire write_lock

 * B can't acquire j_commit_mutex and sleep

 * A can't acquire write lock anymore

 * deadlock

 *

 * What we do here is avoiding such deadlock by playing the same game

 * than the Bkl: if we can't acquire a mutex that depends on the write lock,

 * we release the write lock, wait a bit and then retry.

 *

 * The mutexes concerned by this hack are:

 * - The commit mutex of a journal list

 * - The flush mutex

 * - The journal lock

 */

static inline void reiserfs_mutex_lock_safe(struct mutex *m,

			       struct super_block *s)

{

	reiserfs_write_unlock(s);

	mutex_lock(m);

	reiserfs_write_lock(s);

}



/* lock the current transaction */

static inline void lock_journal(struct super_block *sb)

{

fs/reiserfs/xattr.c

+2 −2
Original line number Diff line number Diff line
@@ -975,7 +975,7 @@ int reiserfs_lookup_privroot(struct super_block *s) 
	int err = 0;



	/* If we don't have the privroot located yet - go find it */

	mutex_lock(&s->s_root->d_inode->i_mutex);

	reiserfs_mutex_lock_safe(&s->s_root->d_inode->i_mutex, s);

	dentry = lookup_one_len(PRIVROOT_NAME, s->s_root,

				strlen(PRIVROOT_NAME));

	if (!IS_ERR(dentry)) {
@@ -1011,7 +1011,7 @@ int reiserfs_xattr_init(struct super_block *s, int mount_flags) 


	if (privroot->d_inode) {

		s->s_xattr = reiserfs_xattr_handlers;

		mutex_lock(&privroot->d_inode->i_mutex);

		reiserfs_mutex_lock_safe(&privroot->d_inode->i_mutex, s);

		if (!REISERFS_SB(s)->xattr_root) {

			struct dentry *dentry;

			dentry = lookup_one_len(XAROOT_NAME, privroot,

include/linux/reiserfs_fs.h

+35 −0
Original line number Diff line number Diff line
@@ -62,6 +62,41 @@ void reiserfs_write_unlock(struct super_block *s); 
int reiserfs_write_lock_once(struct super_block *s);

void reiserfs_write_unlock_once(struct super_block *s, int lock_depth);



/*

 * Several mutexes depend on the write lock.

 * However sometimes we want to relax the write lock while we hold

 * these mutexes, according to the release/reacquire on schedule()

 * properties of the Bkl that were used.

 * Reiserfs performances and locking were based on this scheme.

 * Now that the write lock is a mutex and not the bkl anymore, doing so

 * may result in a deadlock:

 *

 * A acquire write_lock

 * A acquire j_commit_mutex

 * A release write_lock and wait for something

 * B acquire write_lock

 * B can't acquire j_commit_mutex and sleep

 * A can't acquire write lock anymore

 * deadlock

 *

 * What we do here is avoiding such deadlock by playing the same game

 * than the Bkl: if we can't acquire a mutex that depends on the write lock,

 * we release the write lock, wait a bit and then retry.

 *

 * The mutexes concerned by this hack are:

 * - The commit mutex of a journal list

 * - The flush mutex

 * - The journal lock

 * - The inode mutex

 */

static inline void reiserfs_mutex_lock_safe(struct mutex *m,

			       struct super_block *s)

{

	reiserfs_write_unlock(s);

	mutex_lock(m);

	reiserfs_write_lock(s);

}



/*

 * When we schedule, we usually want to also release the write lock,

 * according to the previous bkl based locking scheme of reiserfs.

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