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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: Frederic Weisbecker <fweisbec@gmail.com>
This commit is contained in:
Frederic Weisbecker 2009-05-16 18:12:08 +02:00
parent 2ac626955e
commit c72e05756b
3 changed files with 37 additions and 36 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

34
fs/reiserfs/journal.c
View File

@ -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)
{

4
fs/reiserfs/xattr.c
View File

@ -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,

35
include/linux/reiserfs_fs.h
View File

@ -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.