reiserfs, kill-the-BKL: fix unsafe j_flush_mutex lock

[linux-2.6-block.git] / fs / reiserfs / lock.c

#include <linux/reiserfs_fs.h>
#include <linux/mutex.h>

/*
 * The previous reiserfs locking scheme was heavily based on
 * the tricky properties of the Bkl:
 *
 * - it was acquired recursively by a same task
 * - the performances relied on the release-while-schedule() property
 *
 * Now that we replace it by a mutex, we still want to keep the same
 * recursive property to avoid big changes in the code structure.
 * We use our own lock_owner here because the owner field on a mutex
 * is only available in SMP or mutex debugging, also we only need this field
 * for this mutex, no need for a system wide mutex facility.
 *
 * Also this lock is often released before a call that could block because
 * reiserfs performances were partialy based on the release while schedule()
 * property of the Bkl.
 */
void reiserfs_write_lock(struct super_block *s)
{
	struct reiserfs_sb_info *sb_i = REISERFS_SB(s);

	if (sb_i->lock_owner != current) {
		mutex_lock(&sb_i->lock);
		sb_i->lock_owner = current;
	}

	/* No need to protect it, only the current task touches it */
	sb_i->lock_depth++;
}

void reiserfs_write_unlock(struct super_block *s)
{
	struct reiserfs_sb_info *sb_i = REISERFS_SB(s);

	/*
	 * Are we unlocking without even holding the lock?
	 * Such a situation could even raise a BUG() if we don't
	 * want the data become corrupted
	 */
	WARN_ONCE(sb_i->lock_owner != current,
		  "Superblock write lock imbalance");

	if (--sb_i->lock_depth == -1) {
		sb_i->lock_owner = NULL;
		mutex_unlock(&sb_i->lock);
	}
}

/*
 * Utility function to force a BUG if it is called without the superblock
 * write lock held.  caller is the string printed just before calling BUG()
 */
void reiserfs_check_lock_depth(struct super_block *sb, char *caller)
{
	struct reiserfs_sb_info *sb_i = REISERFS_SB(sb);

	if (sb_i->lock_depth < 0)
		reiserfs_panic(sb, "%s called without kernel lock held %d",
			       caller);
}