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Commit 0720b315 authored by Miklos Szeredi's avatar Miklos Szeredi Committed by Linus Torvalds
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[PATCH] fuse: simplify locking 



This is in preparation for removing the global spinlock in favor of a
per-mount one.

The only critical part is the interaction between fuse_dev_release() and
fuse_fill_super(): fuse_dev_release() must see the assignment to
file->private_data, otherwise it will leak the reference to fuse_conn.

This is ensured by the fput() operation, which will synchronize the assignment
with other CPU's that may do a final fput() soon after this.

Also redundant locking is removed from fuse_fill_super(), where exclusion is
already ensured by the BKL held for this function by the VFS.

Signed-off-by: default avatarMiklos Szeredi <miklos@szeredi.hu>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent e5ac1d1e

fs/fuse/dev.c

+11 −20
Original line number Diff line number Diff line
@@ -23,13 +23,11 @@ static kmem_cache_t *fuse_req_cachep; 


static struct fuse_conn *fuse_get_conn(struct file *file)

{

	struct fuse_conn *fc;

	spin_lock(&fuse_lock);

	fc = file->private_data;

	if (fc && !fc->connected)

		fc = NULL;

	spin_unlock(&fuse_lock);

	return fc;

	/*

	 * Lockless access is OK, because file->private data is set

	 * once during mount and is valid until the file is released.

	 */

	return file->private_data;

}



static void fuse_request_init(struct fuse_req *req)
@@ -607,19 +605,16 @@ static ssize_t fuse_dev_readv(struct file *file, const struct iovec *iov, 
			      unsigned long nr_segs, loff_t *off)

{

	int err;

	struct fuse_conn *fc;

	struct fuse_req *req;

	struct fuse_in *in;

	struct fuse_copy_state cs;

	unsigned reqsize;

	struct fuse_conn *fc = fuse_get_conn(file);

	if (!fc)

		return -EPERM;



 restart:

	spin_lock(&fuse_lock);

	fc = file->private_data;

	err = -EPERM;

	if (!fc)

		goto err_unlock;



	err = -EAGAIN;

	if ((file->f_flags & O_NONBLOCK) && fc->connected &&

	    list_empty(&fc->pending))
@@ -915,17 +910,13 @@ void fuse_abort_conn(struct fuse_conn *fc) 


static int fuse_dev_release(struct inode *inode, struct file *file)

{

	struct fuse_conn *fc;



	spin_lock(&fuse_lock);

	fc = file->private_data;

	struct fuse_conn *fc = fuse_get_conn(file);

	if (fc) {

		spin_lock(&fuse_lock);

		fc->connected = 0;

		end_requests(fc, &fc->pending);

		end_requests(fc, &fc->processing);

	}

		spin_unlock(&fuse_lock);

	if (fc) {

		fasync_helper(-1, file, 0, &fc->fasync);

		kobject_put(&fc->kobj);

	}

fs/fuse/inode.c

+22 −42
Original line number Diff line number Diff line
@@ -414,37 +414,6 @@ static struct fuse_conn *new_conn(void) 
	return fc;

}



static struct fuse_conn *get_conn(struct file *file, struct super_block *sb)

{

	struct fuse_conn *fc;

	int err;



	err = -EINVAL;

	if (file->f_op != &fuse_dev_operations)

		goto out_err;



	err = -ENOMEM;

	fc = new_conn();

	if (!fc)

		goto out_err;



	spin_lock(&fuse_lock);

	err = -EINVAL;

	if (file->private_data)

		goto out_unlock;



	kobject_get(&fc->kobj);

	file->private_data = fc;

	spin_unlock(&fuse_lock);

	return fc;



 out_unlock:

	spin_unlock(&fuse_lock);

	kobject_put(&fc->kobj);

 out_err:

	return ERR_PTR(err);

}



static struct inode *get_root_inode(struct super_block *sb, unsigned mode)

{

	struct fuse_attr attr;
@@ -526,12 +495,9 @@ static void fuse_send_init(struct fuse_conn *fc) 


static unsigned long long conn_id(void)

{

	/* BKL is held for ->get_sb() */

	static unsigned long long ctr = 1;

	unsigned long long val;

	spin_lock(&fuse_lock);

	val = ctr++;

	spin_unlock(&fuse_lock);

	return val;

	return ctr++;

}



static int fuse_fill_super(struct super_block *sb, void *data, int silent)
@@ -556,10 +522,17 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent) 
	if (!file)

		return -EINVAL;



	fc = get_conn(file, sb);

	fput(file);

	if (IS_ERR(fc))

		return PTR_ERR(fc);

	if (file->f_op != &fuse_dev_operations)

		return -EINVAL;



	/* Setting file->private_data can't race with other mount()

	   instances, since BKL is held for ->get_sb() */

	if (file->private_data)

		return -EINVAL;



	fc = new_conn();

	if (!fc)

		return -ENOMEM;



	fc->flags = d.flags;

	fc->user_id = d.user_id;
@@ -589,10 +562,16 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent) 
		goto err_put_root;



	sb->s_root = root_dentry;

	spin_lock(&fuse_lock);

	fc->mounted = 1;

	fc->connected = 1;

	spin_unlock(&fuse_lock);

	kobject_get(&fc->kobj);

	file->private_data = fc;

	/*

	 * atomic_dec_and_test() in fput() provides the necessary

	 * memory barrier for file->private_data to be visible on all

	 * CPUs after this

	 */

	fput(file);



	fuse_send_init(fc);
@@ -601,6 +580,7 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent) 
 err_put_root:

	dput(root_dentry);

 err:

	fput(file);

	kobject_put(&fc->kobj);

	return err;

}