Re: [PATCH 09/27] fs: Push mnt_want_write() outside of i_mutex

[Joel Becker]

On Mon, Apr 16, 2012 at 06:13:47PM +0200, Jan Kara wrote:
> Currently, mnt_want_write() is sometimes called with i_mutex held and sometimes
> without it. This isn't really a problem because mnt_want_write() is a
> non-blocking operation (essentially has a trylock semantics) but when the
> function starts to handle also frozen filesystems, it will get a full lock
> semantics and thus proper lock ordering has to be established. So move
> all mnt_want_write() calls outside of i_mutex.
> 
> One non-trivial case needing conversion is kern_path_create() /
> user_path_create() which didn't include mnt_want_write() but now needs to
> because it acquires i_mutex.  Because there are virtual file systems which
> don't bother with freeze / remount-ro protection we actually provide both
> versions of the function - one which calls mnt_want_write() and one which does
> not.
> 
> CC: ocfs2-devel@xxxxxxxxxxxxxx
> CC: Mark Fasheh <mfasheh@xxxxxxxx>
> CC: Joel Becker <jlbec@xxxxxxxxxxxx>
> CC: "David S. Miller" <davem@xxxxxxxxxxxxx>
> BugLink: https://bugs.launchpad.net/bugs/897421
> Tested-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
> Tested-by: Peter M. Petrakis <peter.petrakis@xxxxxxxxxxxxx>
> Tested-by: Dann Frazier <dann.frazier@xxxxxxxxxxxxx>
> Tested-by: Massimo Morana <massimo.morana@xxxxxxxxxxxxx>
> Signed-off-by: Jan Kara <jack@xxxxxxx>

Acked-by: Joel Becker <jlbec@xxxxxxxxxxxx>

> ---
>  fs/namei.c              |  115 +++++++++++++++++++++++++++--------------------
>  fs/ocfs2/refcounttree.c |   10 +---
>  include/linux/namei.h   |    2 +
>  net/unix/af_unix.c      |   13 ++----
>  4 files changed, 74 insertions(+), 66 deletions(-)
> 
> diff --git a/fs/namei.c b/fs/namei.c
> index 0062dd1..5417fa1 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -2460,7 +2460,9 @@ struct file *do_file_open_root(struct dentry *dentry, struct vfsmount *mnt,
>  	return file;
>  }
>  
> -struct dentry *kern_path_create(int dfd, const char *pathname, struct path *path, int is_dir)
> +static struct dentry *do_kern_path_create(int dfd, const char *pathname,
> +					  struct path *path, int is_dir,
> +					  int freeze_protect)
>  {
>  	struct dentry *dentry = ERR_PTR(-EEXIST);
>  	struct nameidata nd;
> @@ -2478,6 +2480,14 @@ struct dentry *kern_path_create(int dfd, const char *pathname, struct path *path
>  	nd.flags |= LOOKUP_CREATE | LOOKUP_EXCL;
>  	nd.intent.open.flags = O_EXCL;
>  
> +	if (freeze_protect) {
> +		error = mnt_want_write(nd.path.mnt);
> +		if (error) {
> +			dentry = ERR_PTR(error);
> +			goto out;
> +		}
> +	}
> +
>  	/*
>  	 * Do the final lookup.
>  	 */
> @@ -2506,24 +2516,49 @@ eexist:
>  	dentry = ERR_PTR(-EEXIST);
>  fail:
>  	mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
> +	if (freeze_protect)
> +		mnt_drop_write(nd.path.mnt);
>  out:
>  	path_put(&nd.path);
>  	return dentry;
>  }
> +
> +struct dentry *kern_path_create(int dfd, const char *pathname, struct path *path, int is_dir)
> +{
> +	return do_kern_path_create(dfd, pathname, path, is_dir, 0);
> +}
>  EXPORT_SYMBOL(kern_path_create);
>  
> +struct dentry *kern_path_create_thawed(int dfd, const char *pathname, struct path *path, int is_dir)
> +{
> +	return do_kern_path_create(dfd, pathname, path, is_dir, 1);
> +}
> +EXPORT_SYMBOL(kern_path_create_thawed);
> +
>  struct dentry *user_path_create(int dfd, const char __user *pathname, struct path *path, int is_dir)
>  {
>  	char *tmp = getname(pathname);
>  	struct dentry *res;
>  	if (IS_ERR(tmp))
>  		return ERR_CAST(tmp);
> -	res = kern_path_create(dfd, tmp, path, is_dir);
> +	res = do_kern_path_create(dfd, tmp, path, is_dir, 0);
>  	putname(tmp);
>  	return res;
>  }
>  EXPORT_SYMBOL(user_path_create);
>  
> +struct dentry *user_path_create_thawed(int dfd, const char __user *pathname, struct path *path, int is_dir)
> +{
> +	char *tmp = getname(pathname);
> +	struct dentry *res;
> +	if (IS_ERR(tmp))
> +		return ERR_CAST(tmp);
> +	res = do_kern_path_create(dfd, tmp, path, is_dir, 1);
> +	putname(tmp);
> +	return res;
> +}
> +EXPORT_SYMBOL(user_path_create_thawed);
> +
>  int vfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
>  {
>  	int error = may_create(dir, dentry);
> @@ -2579,7 +2614,7 @@ SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, filename, umode_t, mode,
>  	if (S_ISDIR(mode))
>  		return -EPERM;
>  
> -	dentry = user_path_create(dfd, filename, &path, 0);
> +	dentry = user_path_create_thawed(dfd, filename, &path, 0);
>  	if (IS_ERR(dentry))
>  		return PTR_ERR(dentry);
>  
> @@ -2588,12 +2623,9 @@ SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, filename, umode_t, mode,
>  	error = may_mknod(mode);
>  	if (error)
>  		goto out_dput;
> -	error = mnt_want_write(path.mnt);
> -	if (error)
> -		goto out_dput;
>  	error = security_path_mknod(&path, dentry, mode, dev);
>  	if (error)
> -		goto out_drop_write;
> +		goto out_dput;
>  	switch (mode & S_IFMT) {
>  		case 0: case S_IFREG:
>  			error = vfs_create(path.dentry->d_inode,dentry,mode,NULL);
> @@ -2606,11 +2638,10 @@ SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, filename, umode_t, mode,
>  			error = vfs_mknod(path.dentry->d_inode,dentry,mode,0);
>  			break;
>  	}
> -out_drop_write:
> -	mnt_drop_write(path.mnt);
>  out_dput:
>  	dput(dentry);
>  	mutex_unlock(&path.dentry->d_inode->i_mutex);
> +	mnt_drop_write(path.mnt);
>  	path_put(&path);
>  
>  	return error;
> @@ -2652,24 +2683,20 @@ SYSCALL_DEFINE3(mkdirat, int, dfd, const char __user *, pathname, umode_t, mode)
>  	struct path path;
>  	int error;
>  
> -	dentry = user_path_create(dfd, pathname, &path, 1);
> +	dentry = user_path_create_thawed(dfd, pathname, &path, 1);
>  	if (IS_ERR(dentry))
>  		return PTR_ERR(dentry);
>  
>  	if (!IS_POSIXACL(path.dentry->d_inode))
>  		mode &= ~current_umask();
> -	error = mnt_want_write(path.mnt);
> -	if (error)
> -		goto out_dput;
>  	error = security_path_mkdir(&path, dentry, mode);
>  	if (error)
> -		goto out_drop_write;
> +		goto out_dput;
>  	error = vfs_mkdir(path.dentry->d_inode, dentry, mode);
> -out_drop_write:
> -	mnt_drop_write(path.mnt);
>  out_dput:
>  	dput(dentry);
>  	mutex_unlock(&path.dentry->d_inode->i_mutex);
> +	mnt_drop_write(path.mnt);
>  	path_put(&path);
>  	return error;
>  }
> @@ -2764,6 +2791,9 @@ static long do_rmdir(int dfd, const char __user *pathname)
>  	}
>  
>  	nd.flags &= ~LOOKUP_PARENT;
> +	error = mnt_want_write(nd.path.mnt);
> +	if (error)
> +		goto exit1;
>  
>  	mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
>  	dentry = lookup_hash(&nd);
> @@ -2774,19 +2804,15 @@ static long do_rmdir(int dfd, const char __user *pathname)
>  		error = -ENOENT;
>  		goto exit3;
>  	}
> -	error = mnt_want_write(nd.path.mnt);
> -	if (error)
> -		goto exit3;
>  	error = security_path_rmdir(&nd.path, dentry);
>  	if (error)
> -		goto exit4;
> +		goto exit3;
>  	error = vfs_rmdir(nd.path.dentry->d_inode, dentry);
> -exit4:
> -	mnt_drop_write(nd.path.mnt);
>  exit3:
>  	dput(dentry);
>  exit2:
>  	mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
> +	mnt_drop_write(nd.path.mnt);
>  exit1:
>  	path_put(&nd.path);
>  	putname(name);
> @@ -2853,6 +2879,9 @@ static long do_unlinkat(int dfd, const char __user *pathname)
>  		goto exit1;
>  
>  	nd.flags &= ~LOOKUP_PARENT;
> +	error = mnt_want_write(nd.path.mnt);
> +	if (error)
> +		goto exit1;
>  
>  	mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
>  	dentry = lookup_hash(&nd);
> @@ -2865,21 +2894,17 @@ static long do_unlinkat(int dfd, const char __user *pathname)
>  		if (!inode)
>  			goto slashes;
>  		ihold(inode);
> -		error = mnt_want_write(nd.path.mnt);
> -		if (error)
> -			goto exit2;
>  		error = security_path_unlink(&nd.path, dentry);
>  		if (error)
> -			goto exit3;
> +			goto exit2;
>  		error = vfs_unlink(nd.path.dentry->d_inode, dentry);
> -exit3:
> -		mnt_drop_write(nd.path.mnt);
> -	exit2:
> +exit2:
>  		dput(dentry);
>  	}
>  	mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
>  	if (inode)
>  		iput(inode);	/* truncate the inode here */
> +	mnt_drop_write(nd.path.mnt);
>  exit1:
>  	path_put(&nd.path);
>  	putname(name);
> @@ -2939,23 +2964,19 @@ SYSCALL_DEFINE3(symlinkat, const char __user *, oldname,
>  	if (IS_ERR(from))
>  		return PTR_ERR(from);
>  
> -	dentry = user_path_create(newdfd, newname, &path, 0);
> +	dentry = user_path_create_thawed(newdfd, newname, &path, 0);
>  	error = PTR_ERR(dentry);
>  	if (IS_ERR(dentry))
>  		goto out_putname;
>  
> -	error = mnt_want_write(path.mnt);
> -	if (error)
> -		goto out_dput;
>  	error = security_path_symlink(&path, dentry, from);
>  	if (error)
> -		goto out_drop_write;
> +		goto out_dput;
>  	error = vfs_symlink(path.dentry->d_inode, dentry, from);
> -out_drop_write:
> -	mnt_drop_write(path.mnt);
>  out_dput:
>  	dput(dentry);
>  	mutex_unlock(&path.dentry->d_inode->i_mutex);
> +	mnt_drop_write(path.mnt);
>  	path_put(&path);
>  out_putname:
>  	putname(from);
> @@ -3048,7 +3069,7 @@ SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
>  	if (error)
>  		return error;
>  
> -	new_dentry = user_path_create(newdfd, newname, &new_path, 0);
> +	new_dentry = user_path_create_thawed(newdfd, newname, &new_path, 0);
>  	error = PTR_ERR(new_dentry);
>  	if (IS_ERR(new_dentry))
>  		goto out;
> @@ -3056,18 +3077,14 @@ SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
>  	error = -EXDEV;
>  	if (old_path.mnt != new_path.mnt)
>  		goto out_dput;
> -	error = mnt_want_write(new_path.mnt);
> -	if (error)
> -		goto out_dput;
>  	error = security_path_link(old_path.dentry, &new_path, new_dentry);
>  	if (error)
> -		goto out_drop_write;
> +		goto out_dput;
>  	error = vfs_link(old_path.dentry, new_path.dentry->d_inode, new_dentry);
> -out_drop_write:
> -	mnt_drop_write(new_path.mnt);
>  out_dput:
>  	dput(new_dentry);
>  	mutex_unlock(&new_path.dentry->d_inode->i_mutex);
> +	mnt_drop_write(new_path.mnt);
>  	path_put(&new_path);
>  out:
>  	path_put(&old_path);
> @@ -3264,6 +3281,10 @@ SYSCALL_DEFINE4(renameat, int, olddfd, const char __user *, oldname,
>  	if (newnd.last_type != LAST_NORM)
>  		goto exit2;
>  
> +	error = mnt_want_write(oldnd.path.mnt);
> +	if (error)
> +		goto exit2;
> +
>  	oldnd.flags &= ~LOOKUP_PARENT;
>  	newnd.flags &= ~LOOKUP_PARENT;
>  	newnd.flags |= LOOKUP_RENAME_TARGET;
> @@ -3299,23 +3320,19 @@ SYSCALL_DEFINE4(renameat, int, olddfd, const char __user *, oldname,
>  	if (new_dentry == trap)
>  		goto exit5;
>  
> -	error = mnt_want_write(oldnd.path.mnt);
> -	if (error)
> -		goto exit5;
>  	error = security_path_rename(&oldnd.path, old_dentry,
>  				     &newnd.path, new_dentry);
>  	if (error)
> -		goto exit6;
> +		goto exit5;
>  	error = vfs_rename(old_dir->d_inode, old_dentry,
>  				   new_dir->d_inode, new_dentry);
> -exit6:
> -	mnt_drop_write(oldnd.path.mnt);
>  exit5:
>  	dput(new_dentry);
>  exit4:
>  	dput(old_dentry);
>  exit3:
>  	unlock_rename(new_dir, old_dir);
> +	mnt_drop_write(oldnd.path.mnt);
>  exit2:
>  	path_put(&newnd.path);
>  	putname(to);
> diff --git a/fs/ocfs2/refcounttree.c b/fs/ocfs2/refcounttree.c
> index cf78233..a99b8e2 100644
> --- a/fs/ocfs2/refcounttree.c
> +++ b/fs/ocfs2/refcounttree.c
> @@ -4453,7 +4453,7 @@ int ocfs2_reflink_ioctl(struct inode *inode,
>  		return error;
>  	}
>  
> -	new_dentry = user_path_create(AT_FDCWD, newname, &new_path, 0);
> +	new_dentry = user_path_create_thawed(AT_FDCWD, newname, &new_path, 0);
>  	error = PTR_ERR(new_dentry);
>  	if (IS_ERR(new_dentry)) {
>  		mlog_errno(error);
> @@ -4466,19 +4466,13 @@ int ocfs2_reflink_ioctl(struct inode *inode,
>  		goto out_dput;
>  	}
>  
> -	error = mnt_want_write(new_path.mnt);
> -	if (error) {
> -		mlog_errno(error);
> -		goto out_dput;
> -	}
> -
>  	error = ocfs2_vfs_reflink(old_path.dentry,
>  				  new_path.dentry->d_inode,
>  				  new_dentry, preserve);
> -	mnt_drop_write(new_path.mnt);
>  out_dput:
>  	dput(new_dentry);
>  	mutex_unlock(&new_path.dentry->d_inode->i_mutex);
> +	mnt_drop_write(new_path.mnt);
>  	path_put(&new_path);
>  out:
>  	path_put(&old_path);
> diff --git a/include/linux/namei.h b/include/linux/namei.h
> index ffc0213..432f6bb 100644
> --- a/include/linux/namei.h
> +++ b/include/linux/namei.h
> @@ -77,7 +77,9 @@ extern int user_path_at_empty(int, const char __user *, unsigned, struct path *,
>  extern int kern_path(const char *, unsigned, struct path *);
>  
>  extern struct dentry *kern_path_create(int, const char *, struct path *, int);
> +extern struct dentry *kern_path_create_thawed(int, const char *, struct path *, int);
>  extern struct dentry *user_path_create(int, const char __user *, struct path *, int);
> +extern struct dentry *user_path_create_thawed(int, const char __user *, struct path *, int);
>  extern int kern_path_parent(const char *, struct nameidata *);
>  extern int vfs_path_lookup(struct dentry *, struct vfsmount *,
>  			   const char *, unsigned int, struct path *);
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index d510353..c532632 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -865,7 +865,7 @@ static int unix_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
>  		 * Get the parent directory, calculate the hash for last
>  		 * component.
>  		 */
> -		dentry = kern_path_create(AT_FDCWD, sun_path, &path, 0);
> +		dentry = kern_path_create_thawed(AT_FDCWD, sun_path, &path, 0);
>  		err = PTR_ERR(dentry);
>  		if (IS_ERR(dentry))
>  			goto out_mknod_parent;
> @@ -875,19 +875,13 @@ static int unix_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
>  		 */
>  		mode = S_IFSOCK |
>  		       (SOCK_INODE(sock)->i_mode & ~current_umask());
> -		err = mnt_want_write(path.mnt);
> -		if (err)
> -			goto out_mknod_dput;
>  		err = security_path_mknod(&path, dentry, mode, 0);
>  		if (err)
> -			goto out_mknod_drop_write;
> -		err = vfs_mknod(path.dentry->d_inode, dentry, mode, 0);
> -out_mknod_drop_write:
> -		mnt_drop_write(path.mnt);
> -		if (err)
>  			goto out_mknod_dput;
> +		err = vfs_mknod(path.dentry->d_inode, dentry, mode, 0);
>  		mutex_unlock(&path.dentry->d_inode->i_mutex);
>  		dput(path.dentry);
> +		mnt_drop_write(path.mnt);
>  		path.dentry = dentry;
>  
>  		addr->hash = UNIX_HASH_SIZE;
> @@ -924,6 +918,7 @@ out:
>  out_mknod_dput:
>  	dput(dentry);
>  	mutex_unlock(&path.dentry->d_inode->i_mutex);
> +	mnt_drop_write(path.mnt);
>  	path_put(&path);
>  out_mknod_parent:
>  	if (err == -EEXIST)
> -- 
> 1.7.1
> 

-- 

"Hell is oneself, hell is alone, the other figures in it, merely projections."
        - T. S. Eliot

			http://www.jlbec.org/
			jlbec@xxxxxxxxxxxx
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