Commit 23bfc2a2 authored by NeilBrown's avatar NeilBrown Committed by Linus Torvalds
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autofs4: allow RCU-walk to walk through autofs4 



This series teaches autofs about RCU-walk so that we don't drop straight
into REF-walk when we hit an autofs directory, and so that we avoid
spinlocks as much as possible when performing an RCU-walk.

This is needed so that the benefits of the recent NFS support for
RCU-walk are fully available when NFS filesystems are automounted.

Patches have been carefully reviewed and tested both with test suites
and in production - thanks a lot to Ian Kent for his support there.

This patch (of 6):

Any attempt to look up a pathname that passes though an autofs4 mount is
currently forced out of RCU-walk into REF-walk.

This can significantly hurt performance of many-thread work loads on
many-core systems, especially if the automounted filesystem supports
RCU-walk but doesn't get to benefit from it.

So if autofs4_d_manage is called with rcu_walk set, only fail with -ECHILD
if it is necessary to wait longer than a spinlock.

Signed-off-by: default avatarNeilBrown <neilb@suse.de>
Reviewed-by: default avatarIan Kent <raven@themaw.net>
Tested-by: default avatarIan Kent <raven@themaw.net>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 8a273345

fs/autofs4/autofs_i.h

+1 −1
Original line number Diff line number Diff line
@@ -148,7 +148,7 @@ void autofs4_free_ino(struct autofs_info *); 


/* Expiration */

int is_autofs4_dentry(struct dentry *);

int autofs4_expire_wait(struct dentry *dentry);

int autofs4_expire_wait(struct dentry *dentry, int rcu_walk);

int autofs4_expire_run(struct super_block *, struct vfsmount *,

			struct autofs_sb_info *,

			struct autofs_packet_expire __user *);

fs/autofs4/dev-ioctl.c

+1 −1
Original line number Diff line number Diff line
@@ -450,7 +450,7 @@ static int autofs_dev_ioctl_requester(struct file *fp, 
	ino = autofs4_dentry_ino(path.dentry);

	if (ino) {

		err = 0;

		autofs4_expire_wait(path.dentry);

		autofs4_expire_wait(path.dentry, 0);

		spin_lock(&sbi->fs_lock);

		param->requester.uid = from_kuid_munged(current_user_ns(), ino->uid);

		param->requester.gid = from_kgid_munged(current_user_ns(), ino->gid);

fs/autofs4/expire.c

+3 −1
Original line number Diff line number Diff line
@@ -461,7 +461,7 @@ found: 
	return expired;

}



int autofs4_expire_wait(struct dentry *dentry)

int autofs4_expire_wait(struct dentry *dentry, int rcu_walk)

{

	struct autofs_sb_info *sbi = autofs4_sbi(dentry->d_sb);

	struct autofs_info *ino = autofs4_dentry_ino(dentry);
@@ -471,6 +471,8 @@ int autofs4_expire_wait(struct dentry *dentry) 
	spin_lock(&sbi->fs_lock);

	if (ino->flags & AUTOFS_INF_EXPIRING) {

		spin_unlock(&sbi->fs_lock);

		if (rcu_walk)

			return -ECHILD;



		DPRINTK("waiting for expire %p name=%.*s",

			 dentry, dentry->d_name.len, dentry->d_name.name);

fs/autofs4/root.c

+29 −15
Original line number Diff line number Diff line
@@ -210,7 +210,8 @@ next: 
	return NULL;

}



static struct dentry *autofs4_lookup_expiring(struct dentry *dentry)

static struct dentry *autofs4_lookup_expiring(struct dentry *dentry,

					      bool rcu_walk)

{

	struct autofs_sb_info *sbi = autofs4_sbi(dentry->d_sb);

	struct dentry *parent = dentry->d_parent;
@@ -229,6 +230,11 @@ static struct dentry *autofs4_lookup_expiring(struct dentry *dentry) 
		struct dentry *expiring;

		struct qstr *qstr;



		if (rcu_walk) {

			spin_unlock(&sbi->lookup_lock);

			return ERR_PTR(-ECHILD);

		}



		ino = list_entry(p, struct autofs_info, expiring);

		expiring = ino->dentry;
@@ -264,13 +270,15 @@ next: 
	return NULL;

}



static int autofs4_mount_wait(struct dentry *dentry)

static int autofs4_mount_wait(struct dentry *dentry, bool rcu_walk)

{

	struct autofs_sb_info *sbi = autofs4_sbi(dentry->d_sb);

	struct autofs_info *ino = autofs4_dentry_ino(dentry);

	int status = 0;



	if (ino->flags & AUTOFS_INF_PENDING) {

		if (rcu_walk)

			return -ECHILD;

		DPRINTK("waiting for mount name=%.*s",

			dentry->d_name.len, dentry->d_name.name);

		status = autofs4_wait(sbi, dentry, NFY_MOUNT);
@@ -280,20 +288,22 @@ static int autofs4_mount_wait(struct dentry *dentry) 
	return status;

}



static int do_expire_wait(struct dentry *dentry)

static int do_expire_wait(struct dentry *dentry, bool rcu_walk)

{

	struct dentry *expiring;



	expiring = autofs4_lookup_expiring(dentry);

	expiring = autofs4_lookup_expiring(dentry, rcu_walk);

	if (IS_ERR(expiring))

		return PTR_ERR(expiring);

	if (!expiring)

		return autofs4_expire_wait(dentry);

		return autofs4_expire_wait(dentry, rcu_walk);

	else {

		/*

		 * If we are racing with expire the request might not

		 * be quite complete, but the directory has been removed

		 * so it must have been successful, just wait for it.

		 */

		autofs4_expire_wait(expiring);

		autofs4_expire_wait(expiring, 0);

		autofs4_del_expiring(expiring);

		dput(expiring);

	}
@@ -345,7 +355,7 @@ static struct vfsmount *autofs4_d_automount(struct path *path) 
	 * and the directory was removed, so just go ahead and try

	 * the mount.

	 */

	status = do_expire_wait(dentry);

	status = do_expire_wait(dentry, 0);

	if (status && status != -EAGAIN)

		return NULL;
@@ -353,7 +363,7 @@ static struct vfsmount *autofs4_d_automount(struct path *path) 
	spin_lock(&sbi->fs_lock);

	if (ino->flags & AUTOFS_INF_PENDING) {

		spin_unlock(&sbi->fs_lock);

		status = autofs4_mount_wait(dentry);

		status = autofs4_mount_wait(dentry, 0);

		if (status)

			return ERR_PTR(status);

		goto done;
@@ -394,7 +404,7 @@ static struct vfsmount *autofs4_d_automount(struct path *path) 
		}

		ino->flags |= AUTOFS_INF_PENDING;

		spin_unlock(&sbi->fs_lock);

		status = autofs4_mount_wait(dentry);

		status = autofs4_mount_wait(dentry, 0);

		spin_lock(&sbi->fs_lock);

		ino->flags &= ~AUTOFS_INF_PENDING;

		if (status) {
@@ -430,21 +440,25 @@ static int autofs4_d_manage(struct dentry *dentry, bool rcu_walk) 
		return 0;

	}



	/* We need to sleep, so we need pathwalk to be in ref-mode */

	if (rcu_walk)

		return -ECHILD;



	/* Wait for pending expires */

	do_expire_wait(dentry);

	if (do_expire_wait(dentry, rcu_walk) == -ECHILD)

		return -ECHILD;



	/*

	 * This dentry may be under construction so wait on mount

	 * completion.

	 */

	status = autofs4_mount_wait(dentry);

	status = autofs4_mount_wait(dentry, rcu_walk);

	if (status)

		return status;



	if (rcu_walk)

		/* it is always safe to return 0 as the worst that

		 * will happen is we retry in REF-walk mode.

		 * Better than always taking a lock.

		 */

		return 0;



	spin_lock(&sbi->fs_lock);

	/*

	 * If the dentry has been selected for expire while we slept

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