autofs4: d_manage() should return -EISDIR when appropriate in rcu-walk mode. (ef16cc59) · Commits · 戴 / test

If rcu-walk mode we don't *have* to return -EISDIR for non-mount-traps as we will simply drop into REF-walk and handling DCACHE_NEED_AUTOMOUNT dentrys the slow way. But it is better if we do when possible. In 'oz_mode', use the same condition as ref-walk: if not a mountpoint, then it must be -EISDIR. In regular mode there are most tests needed. Most of them can be performed without taking any spinlocks. If we find a directory that isn't obviously empty, and isn't mounted on, we need to call 'simple_empty()' which does take a spinlock. If this turned out to hurt performance, some other approach could be found to signal when a directory is known to be empty. Signed-off-by:

NeilBrown <neilb@suse.de> Reviewed-by:

Ian Kent <raven@themaw.net> Tested-by:

Ian Kent <raven@themaw.net> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

fs/autofs4/root.c

+20 −6

Original line number	Diff line number	Diff line
		@@ -433,8 +433,6 @@ static int autofs4_d_manage(struct dentry *dentry, bool rcu_walk)

		/* The daemon never waits. */
		if (autofs4_oz_mode(sbi)) {
		if (rcu_walk)
		return 0;
		if (!d_mountpoint(dentry))
		return -EISDIR;
		return 0;
		@@ -452,12 +450,28 @@ static int autofs4_d_manage(struct dentry *dentry, bool 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.
		if (rcu_walk) {
		/* We don't need fs_lock in rcu_walk mode,
		* just testing 'AUTOFS_INFO_NO_RCU' is enough.
		* simple_empty() takes a spinlock, so leave it
		* to last.
		* We only return -EISDIR when certain this isn't
		* a mount-trap.
		*/
		struct inode *inode;
		if (ino->flags & (AUTOFS_INF_EXPIRING \| AUTOFS_INF_NO_RCU))
		return 0;
		if (d_mountpoint(dentry))
		return 0;
		inode = ACCESS_ONCE(dentry->d_inode);
		if (inode && S_ISLNK(inode->i_mode))
		return -EISDIR;
		if (list_empty(&dentry->d_subdirs))
		return 0;
		if (!simple_empty(dentry))
		return -EISDIR;
		return 0;
		}

		spin_lock(&sbi->fs_lock);
		/*

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