[PATCH] autofs4: fix infamous "Busy inodes after umount ..." message

If the automount daemon receives a signal which causes it to sumarily
terminate the autofs4 module leaks dentries.  The same problem exists with
detached mount requests without the warning.

This patch cleans these dentries at umount.

Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/autofs4/autofs_i.h

@@ -92,6 +92,7 @@ struct autofs_wait_queue {
 
 struct autofs_sb_info {
 	u32 magic;
+	struct dentry *root;
 	struct file *pipe;
 	pid_t oz_pgrp;
 	int catatonic;

fs/autofs4/inode.c

@@ -16,6 +16,7 @@
 #include <linux/pagemap.h>
 #include <linux/parser.h>
 #include <linux/bitops.h>
+#include <linux/smp_lock.h>
 #include "autofs_i.h"
 #include <linux/module.h>
 
@@ -76,6 +77,66 @@ void autofs4_free_ino(struct autofs_info *ino)
 	kfree(ino);
 }
 
+/*
+ * Deal with the infamous "Busy inodes after umount ..." message.
+ *
+ * Clean up the dentry tree. This happens with autofs if the user
+ * space program goes away due to a SIGKILL, SIGSEGV etc.
+ */
+static void autofs4_force_release(struct autofs_sb_info *sbi)
+{
+	struct dentry *this_parent = sbi->root;
+	struct list_head *next;
+
+	spin_lock(&dcache_lock);
+repeat:
+	next = this_parent->d_subdirs.next;
+resume:
+	while (next != &this_parent->d_subdirs) {
+		struct dentry *dentry = list_entry(next, struct dentry, d_child);
+
+		/* Negative dentry - don`t care */
+		if (!simple_positive(dentry)) {
+			next = next->next;
+			continue;
+		}
+
+		if (!list_empty(&dentry->d_subdirs)) {
+			this_parent = dentry;
+			goto repeat;
+		}
+
+		next = next->next;
+		spin_unlock(&dcache_lock);
+
+		DPRINTK("dentry %p %.*s",
+			dentry, (int)dentry->d_name.len, dentry->d_name.name);
+
+		dput(dentry);
+		spin_lock(&dcache_lock);
+	}
+
+	if (this_parent != sbi->root) {
+		struct dentry *dentry = this_parent;
+
+		next = this_parent->d_child.next;
+		this_parent = this_parent->d_parent;
+		spin_unlock(&dcache_lock);
+		DPRINTK("parent dentry %p %.*s",
+			dentry, (int)dentry->d_name.len, dentry->d_name.name);
+		dput(dentry);
+		spin_lock(&dcache_lock);
+		goto resume;
+	}
+	spin_unlock(&dcache_lock);
+
+	dput(sbi->root);
+	sbi->root = NULL;
+	shrink_dcache_sb(sbi->sb);
+
+	return;
+}
+
 static void autofs4_put_super(struct super_block *sb)
 {
 	struct autofs_sb_info *sbi = autofs4_sbi(sb);
@@ -85,6 +146,10 @@ static void autofs4_put_super(struct super_block *sb)
 	if ( !sbi->catatonic )
 		autofs4_catatonic_mode(sbi); /* Free wait queues, close pipe */
 
+	/* Clean up and release dangling references */
+	if (sbi)
+		autofs4_force_release(sbi);
+
 	kfree(sbi);
 
 	DPRINTK("shutting down");
@@ -199,6 +264,7 @@ int autofs4_fill_super(struct super_block *s, void *data, int silent)
 
 	s->s_fs_info = sbi;
 	sbi->magic = AUTOFS_SBI_MAGIC;
+	sbi->root = NULL;
 	sbi->catatonic = 0;
 	sbi->exp_timeout = 0;
 	sbi->oz_pgrp = process_group(current);
@@ -266,6 +332,13 @@ int autofs4_fill_super(struct super_block *s, void *data, int silent)
 		goto fail_fput;
 	sbi->pipe = pipe;
 
+	/*
+	 * Take a reference to the root dentry so we get a chance to
+	 * clean up the dentry tree on umount.
+	 * See autofs4_force_release.
+	 */
+	sbi->root = dget(root);
+
 	/*
 	 * Success! Install the root dentry now to indicate completion.
 	 */