Attachment 152877 Details for Bug 236875 – Patch to resolve race between mount and expire

[patch] Patch to resolve race between mount and expire

autofs4-2.6.18-rhel5-lookup-expire-race.patch (text/plain), 9.25 KB, created by Ian Kent on 2007-04-18 07:24:52 UTC

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Creator: Ian Kent

Created: 2007-04-18 07:24:52 UTC

Size: 9.25 KB

patch

obsolete

>--- linux-2.6.18.noarch/fs/autofs4/autofs_i.h.lookup-expire-race	2007-04-16 17:21:30.000000000 +0800
>+++ linux-2.6.18.noarch/fs/autofs4/autofs_i.h	2007-04-16 17:22:14.000000000 +0800
>@@ -54,6 +54,8 @@ struct autofs_info {
> 
> 	int		flags;
> 
>+	struct list_head rehash;
>+
> 	struct autofs_sb_info *sbi;
> 	unsigned long last_used;
> 	atomic_t count;
>@@ -112,6 +114,8 @@ struct autofs_sb_info {
> 	struct mutex wq_mutex;
> 	spinlock_t fs_lock;
> 	struct autofs_wait_queue *queues; /* Wait queue pointer */
>+	spinlock_t rehash_lock;
>+	struct list_head rehash_list;
> };
> 
> static inline struct autofs_sb_info *autofs4_sbi(struct super_block *sb)
>--- linux-2.6.18.noarch/fs/autofs4/root.c.lookup-expire-race	2007-04-16 17:21:30.000000000 +0800
>+++ linux-2.6.18.noarch/fs/autofs4/root.c	2007-04-16 17:22:47.000000000 +0800
>@@ -263,7 +263,7 @@ static int try_to_fill_dentry(struct den
> 		 */
> 		status = d_invalidate(dentry);
> 		if (status != -EBUSY)
>-			return -ENOENT;
>+			return -EAGAIN;
> 	}
> 
> 	DPRINTK("dentry=%p %.*s ino=%p",
>@@ -415,6 +415,15 @@ static int autofs4_revalidate(struct den
> 		if (status == 0)
> 			return 1;
> 
>+		/*
>+		 * A status of EAGAIN here means that the dentry has gone
>+		 * away while waiting for an expire to complete. If we are
>+		 * racing with expire lookup will wait for it so this must
>+		 * be a revalidate and we need to send it to lookup.
>+		 */
>+		if (status == -EAGAIN)
>+			return 0;
>+
> 		return status;
> 	}
> 
>@@ -459,6 +468,15 @@ void autofs4_dentry_release(struct dentr
> 	de->d_fsdata = NULL;
> 
> 	if (inf) {
>+		struct autofs_sb_info *sbi = autofs4_sbi(de->d_sb);
>+
>+		if (sbi) {
>+			spin_lock(&sbi->rehash_lock);
>+			if (!list_empty(&inf->rehash))
>+				list_del(&inf->rehash);
>+			spin_unlock(&sbi->rehash_lock);
>+		}
>+
> 		inf->dentry = NULL;
> 		inf->inode = NULL;
> 
>@@ -478,10 +496,80 @@ static struct dentry_operations autofs4_
> 	.d_release	= autofs4_dentry_release,
> };
> 
>+static struct dentry *autofs4_lookup_unhashed(struct autofs_sb_info *sbi, struct dentry *parent, struct qstr *name)
>+{
>+	unsigned int len = name->len;
>+	unsigned int hash = name->hash;
>+	const unsigned char *str = name->name;
>+	struct list_head *p, *head;
>+
>+	spin_lock(&dcache_lock);
>+	spin_lock(&sbi->rehash_lock);
>+	head = &sbi->rehash_list;
>+	list_for_each(p, head) {
>+		struct autofs_info *ino;
>+		struct dentry *dentry;
>+		struct qstr *qstr;
>+
>+		ino = list_entry(p, struct autofs_info, rehash);
>+		dentry = ino->dentry;
>+
>+		spin_lock(&dentry->d_lock);
>+
>+		/* Bad luck, we've already been dentry_iput */
>+		if (!dentry->d_inode)
>+			goto next;
>+
>+		qstr = &dentry->d_name;
>+
>+		if (dentry->d_name.hash != hash)
>+			goto next;
>+		if (dentry->d_parent != parent)
>+			goto next;
>+
>+		if (qstr->len != len)
>+			goto next;
>+		if (memcmp(qstr->name, str, len))
>+			goto next;
>+
>+		if (d_unhashed(dentry)) {
>+			struct autofs_info *ino = autofs4_dentry_ino(dentry);
>+			struct inode *inode = dentry->d_inode;
>+
>+			list_del_init(&ino->rehash);
>+			dget(dentry);
>+			/*
>+			 * Make the rehashed dentry negative so the VFS
>+			 * behaves as it should.
>+			 */
>+			if (inode) {
>+				dentry->d_inode = NULL;
>+				list_del_init(&dentry->d_alias);
>+				spin_unlock(&dentry->d_lock);
>+				spin_unlock(&sbi->rehash_lock);
>+				spin_unlock(&dcache_lock);
>+				iput(inode);
>+				return dentry;
>+			}
>+			spin_unlock(&dentry->d_lock);
>+			spin_unlock(&sbi->rehash_lock);
>+			spin_unlock(&dcache_lock);
>+			return dentry;
>+		}
>+next:
>+		spin_unlock(&dentry->d_lock);
>+	}
>+	spin_unlock(&sbi->rehash_lock);
>+	spin_unlock(&dcache_lock);
>+
>+	return NULL;
>+}
>+
> /* Lookups in the root directory */
> static struct dentry *autofs4_lookup(struct inode *dir, struct dentry *dentry, struct nameidata *nd)
> {
> 	struct autofs_sb_info *sbi;
>+	struct dentry *unhashed;
> 	int oz_mode;
> 
> 	DPRINTK("name = %.*s",
>@@ -497,25 +585,46 @@ static struct dentry *autofs4_lookup(str
> 	DPRINTK("pid = %u, pgrp = %u, catatonic = %d, oz_mode = %d",
> 		 current->pid, process_group(current), sbi->catatonic, oz_mode);
> 
>-	/*
>-	 * Mark the dentry incomplete, but add it. This is needed so
>-	 * that the VFS layer knows about the dentry, and we can count
>-	 * on catching any lookups through the revalidate.
>-	 *
>-	 * Let all the hard work be done by the revalidate function that
>-	 * needs to be able to do this anyway..
>-	 *
>-	 * We need to do this before we release the directory semaphore.
>-	 */
>-	dentry->d_op = &autofs4_root_dentry_operations;
>+	unhashed = autofs4_lookup_unhashed(sbi, dentry->d_parent, &dentry->d_name);
>+	if (!unhashed) {
>+		/*
>+		 * Mark the dentry incomplete, but add it. This is needed so
>+		 * that the VFS layer knows about the dentry, and we can count
>+		 * on catching any lookups through the revalidate.
>+		 *
>+		 * Let all the hard work be done by the revalidate function that
>+		 * needs to be able to do this anyway..
>+		 *
>+		 * We need to do this before we release the directory semaphore.
>+		 */
>+		dentry->d_op = &autofs4_root_dentry_operations;
>+
>+		dentry->d_fsdata = NULL;
>+		d_add(dentry, NULL);
>+	} else {
>+		struct autofs_info *ino = autofs4_dentry_ino(unhashed);
>+		DPRINTK("rehash %p with %p", dentry, unhashed);
>+		/*
>+		 * 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, so just wait for it.
>+		 */
>+		if (ino && (ino->flags & AUTOFS_INF_EXPIRING)) {
>+			DPRINTK("wait for incomplete expire %p name=%.*s",
>+				unhashed, unhashed->d_name.len,
>+				unhashed->d_name.name);
>+			autofs4_wait(sbi, unhashed, NFY_NONE);
>+			DPRINTK("request completed");
>+		}
>+		d_rehash(unhashed);
>+		dentry = unhashed;
>+	}
> 
> 	if (!oz_mode) {
> 		spin_lock(&dentry->d_lock);
> 		dentry->d_flags |= DCACHE_AUTOFS_PENDING;
> 		spin_unlock(&dentry->d_lock);
> 	}
>-	dentry->d_fsdata = NULL;
>-	d_add(dentry, NULL);
> 
> 	if (dentry->d_op && dentry->d_op->d_revalidate) {
> 		mutex_unlock(&dir->i_mutex);
>@@ -534,6 +643,8 @@ static struct dentry *autofs4_lookup(str
> 			if (sigismember (sigset, SIGKILL) ||
> 			    sigismember (sigset, SIGQUIT) ||
> 			    sigismember (sigset, SIGINT)) {
>+			    if (unhashed)
>+				dput(unhashed);
> 			    return ERR_PTR(-ERESTARTNOINTR);
> 			}
> 		}
>@@ -548,8 +659,14 @@ static struct dentry *autofs4_lookup(str
> 	 * doesn't do the right thing for all system calls, but it should
> 	 * be OK for the operations we permit from an autofs.
> 	 */
>-	if (dentry->d_inode && d_unhashed(dentry))
>+	if (dentry->d_inode && d_unhashed(dentry)) {
>+		if (unhashed)
>+			dput(unhashed);
> 		return ERR_PTR(-ENOENT);
>+	}
>+
>+	if (unhashed)
>+		return dentry;
> 
> 	return NULL;
> }
>@@ -611,9 +728,10 @@ static int autofs4_dir_symlink(struct in
>  * Normal filesystems would do a "d_delete()" to tell the VFS dcache
>  * that the file no longer exists. However, doing that means that the
>  * VFS layer can turn the dentry into a negative dentry.  We don't want
>- * this, because since the unlink is probably the result of an expire.
>- * We simply d_drop it, which allows the dentry lookup to remount it
>- * if necessary.
>+ * this, because the unlink is probably the result of an expire.
>+ * We simply d_drop it and add it to a rehash candidates list in the
>+ * super block, which allows the dentry lookup to reuse it retaining
>+ * the flags, such as expire in progress, in case we're racing with expire.
>  *
>  * If a process is blocked on the dentry waiting for the expire to finish,
>  * it will invalidate the dentry and try to mount with a new one.
>@@ -642,7 +760,14 @@ static int autofs4_dir_unlink(struct ino
> 
> 	dir->i_mtime = CURRENT_TIME;
> 
>-	d_drop(dentry);
>+	spin_lock(&dcache_lock);
>+	spin_lock(&sbi->rehash_lock);
>+	list_add(&ino->rehash, &sbi->rehash_list);
>+	spin_unlock(&sbi->rehash_lock);
>+	spin_lock(&dentry->d_lock);
>+	__d_drop(dentry);
>+	spin_unlock(&dentry->d_lock);
>+	spin_unlock(&dcache_lock);
> 
> 	return 0;
> }
>@@ -653,6 +778,9 @@ static int autofs4_dir_rmdir(struct inod
> 	struct autofs_info *ino = autofs4_dentry_ino(dentry);
> 	struct autofs_info *p_ino;
> 	
>+	DPRINTK("dentry %p, removing %.*s",
>+		dentry, dentry->d_name.len, dentry->d_name.name);
>+
> 	if (!autofs4_oz_mode(sbi))
> 		return -EACCES;
> 
>@@ -661,6 +789,9 @@ static int autofs4_dir_rmdir(struct inod
> 		spin_unlock(&dcache_lock);
> 		return -ENOTEMPTY;
> 	}
>+	spin_lock(&sbi->rehash_lock);
>+	list_add(&ino->rehash, &sbi->rehash_list);
>+	spin_unlock(&sbi->rehash_lock);
> 	spin_lock(&dentry->d_lock);
> 	__d_drop(dentry);
> 	spin_unlock(&dentry->d_lock);
>--- linux-2.6.18.noarch/fs/autofs4/inode.c.lookup-expire-race	2007-04-16 17:21:30.000000000 +0800
>+++ linux-2.6.18.noarch/fs/autofs4/inode.c	2007-04-16 17:22:14.000000000 +0800
>@@ -47,6 +47,8 @@ struct autofs_info *autofs4_init_ino(str
> 	ino->dentry = NULL;
> 	ino->size = 0;
> 
>+	INIT_LIST_HEAD(&ino->rehash);
>+
> 	ino->last_used = jiffies;
> 	atomic_set(&ino->count, 0);
> 
>@@ -157,14 +159,13 @@ void autofs4_kill_sb(struct super_block 
> 	if (!sbi)
> 		goto out_kill_sb;
> 
>-	sb->s_fs_info = NULL;
>-
>-	if ( !sbi->catatonic )
>+	if (!sbi->catatonic)
> 		autofs4_catatonic_mode(sbi); /* Free wait queues, close pipe */
> 
> 	/* Clean up and release dangling references */
> 	autofs4_force_release(sbi);
> 
>+	sb->s_fs_info = NULL;
> 	kfree(sbi);
> 
> out_kill_sb:
>@@ -335,6 +336,8 @@ int autofs4_fill_super(struct super_bloc
> 	mutex_init(&sbi->wq_mutex);
> 	spin_lock_init(&sbi->fs_lock);
> 	sbi->queues = NULL;
>+	spin_lock_init(&sbi->rehash_lock);
>+	INIT_LIST_HEAD(&sbi->rehash_list);
> 	s->s_blocksize = 1024;
> 	s->s_blocksize_bits = 10;
> 	s->s_magic = AUTOFS_SUPER_MAGIC;

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Attachments on bug 236875: 152877 | 161844 | 173481 | 173501