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Commit ea01a184 authored by Al Viro's avatar Al Viro
Browse files

autofs races 



* make autofs4_expire_indirect() skip the dentries being in process of
expiry
* do *not* mess with list_move(); making sure that dentry with
AUTOFS_INF_EXPIRING are not picked for expiry is enough.
* do not remove NO_RCU when we set EXPIRING, don't bother with smp_mb()
there.  Clear it at the same time we clear EXPIRING.  Makes a bunch of
tests simpler.
* rename NO_RCU to WANT_EXPIRE, which is what it really is.

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent ba65dc5e

fs/autofs4/autofs_i.h

+6 −2
Original line number Diff line number Diff line
@@ -70,9 +70,13 @@ struct autofs_info { 
};



#define AUTOFS_INF_EXPIRING	(1<<0) /* dentry in the process of expiring */

#define AUTOFS_INF_NO_RCU	(1<<1) /* the dentry is being considered

#define AUTOFS_INF_WANT_EXPIRE	(1<<1) /* the dentry is being considered

					* for expiry, so RCU_walk is

					* not permitted

					* not permitted.  If it progresses to

					* actual expiry attempt, the flag is

					* not cleared when EXPIRING is set -

					* in that case it gets cleared only

					* when it comes to clearing EXPIRING.

					*/

#define AUTOFS_INF_PENDING	(1<<2) /* dentry pending mount */

fs/autofs4/expire.c

+8 −19
Original line number Diff line number Diff line
@@ -316,19 +316,17 @@ struct dentry *autofs4_expire_direct(struct super_block *sb, 
	if (ino->flags & AUTOFS_INF_PENDING)

		goto out;

	if (!autofs4_direct_busy(mnt, root, timeout, do_now)) {

		ino->flags |= AUTOFS_INF_NO_RCU;

		ino->flags |= AUTOFS_INF_WANT_EXPIRE;

		spin_unlock(&sbi->fs_lock);

		synchronize_rcu();

		spin_lock(&sbi->fs_lock);

		if (!autofs4_direct_busy(mnt, root, timeout, do_now)) {

			ino->flags |= AUTOFS_INF_EXPIRING;

			smp_mb();

			ino->flags &= ~AUTOFS_INF_NO_RCU;

			init_completion(&ino->expire_complete);

			spin_unlock(&sbi->fs_lock);

			return root;

		}

		ino->flags &= ~AUTOFS_INF_NO_RCU;

		ino->flags &= ~AUTOFS_INF_WANT_EXPIRE;

	}

out:

	spin_unlock(&sbi->fs_lock);
@@ -446,7 +444,7 @@ struct dentry *autofs4_expire_indirect(struct super_block *sb, 
	while ((dentry = get_next_positive_subdir(dentry, root))) {

		spin_lock(&sbi->fs_lock);

		ino = autofs4_dentry_ino(dentry);

		if (ino->flags & AUTOFS_INF_NO_RCU)

		if (ino->flags & AUTOFS_INF_WANT_EXPIRE)

			expired = NULL;

		else

			expired = should_expire(dentry, mnt, timeout, how);
@@ -455,7 +453,7 @@ struct dentry *autofs4_expire_indirect(struct super_block *sb, 
			continue;

		}

		ino = autofs4_dentry_ino(expired);

		ino->flags |= AUTOFS_INF_NO_RCU;

		ino->flags |= AUTOFS_INF_WANT_EXPIRE;

		spin_unlock(&sbi->fs_lock);

		synchronize_rcu();

		spin_lock(&sbi->fs_lock);
@@ -465,7 +463,7 @@ struct dentry *autofs4_expire_indirect(struct super_block *sb, 
			goto found;

		}



		ino->flags &= ~AUTOFS_INF_NO_RCU;

		ino->flags &= ~AUTOFS_INF_WANT_EXPIRE;

		if (expired != dentry)

			dput(expired);

		spin_unlock(&sbi->fs_lock);
@@ -475,17 +473,8 @@ struct dentry *autofs4_expire_indirect(struct super_block *sb, 
found:

	pr_debug("returning %p %pd\n", expired, expired);

	ino->flags |= AUTOFS_INF_EXPIRING;

	smp_mb();

	ino->flags &= ~AUTOFS_INF_NO_RCU;

	init_completion(&ino->expire_complete);

	spin_unlock(&sbi->fs_lock);

	spin_lock(&sbi->lookup_lock);

	spin_lock(&expired->d_parent->d_lock);

	spin_lock_nested(&expired->d_lock, DENTRY_D_LOCK_NESTED);

	list_move(&expired->d_parent->d_subdirs, &expired->d_child);

	spin_unlock(&expired->d_lock);

	spin_unlock(&expired->d_parent->d_lock);

	spin_unlock(&sbi->lookup_lock);

	return expired;

}
@@ -496,7 +485,7 @@ int autofs4_expire_wait(struct dentry *dentry, int rcu_walk) 
	int status;



	/* Block on any pending expire */

	if (!(ino->flags & (AUTOFS_INF_EXPIRING | AUTOFS_INF_NO_RCU)))

	if (!(ino->flags & AUTOFS_INF_WANT_EXPIRE))

		return 0;

	if (rcu_walk)

		return -ECHILD;
@@ -554,7 +543,7 @@ int autofs4_expire_run(struct super_block *sb, 
	ino = autofs4_dentry_ino(dentry);

	/* avoid rapid-fire expire attempts if expiry fails */

	ino->last_used = now;

	ino->flags &= ~AUTOFS_INF_EXPIRING;

	ino->flags &= ~(AUTOFS_INF_EXPIRING|AUTOFS_INF_WANT_EXPIRE);

	complete_all(&ino->expire_complete);

	spin_unlock(&sbi->fs_lock);
@@ -583,7 +572,7 @@ int autofs4_do_expire_multi(struct super_block *sb, struct vfsmount *mnt, 
		spin_lock(&sbi->fs_lock);

		/* avoid rapid-fire expire attempts if expiry fails */

		ino->last_used = now;

		ino->flags &= ~AUTOFS_INF_EXPIRING;

		ino->flags &= ~(AUTOFS_INF_EXPIRING|AUTOFS_INF_WANT_EXPIRE);

		complete_all(&ino->expire_complete);

		spin_unlock(&sbi->fs_lock);

		dput(dentry);

fs/autofs4/root.c

+1 −1
Original line number Diff line number Diff line
@@ -458,7 +458,7 @@ static int autofs4_d_manage(struct dentry *dentry, bool rcu_walk) 
		 */

		struct inode *inode;



		if (ino->flags & (AUTOFS_INF_EXPIRING | AUTOFS_INF_NO_RCU))

		if (ino->flags & AUTOFS_INF_WANT_EXPIRE)

			return 0;

		if (d_mountpoint(dentry))

			return 0;