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Date: Mon, 16 Apr 2012 19:18:53 -0700
From: Joel Becker <jlbec@...lplan.org>
To: Jan Kara <jack@...e.cz>
Cc: Al Viro <viro@...IV.linux.org.uk>, dchinner@...hat.com,
LKML <linux-kernel@...r.kernel.org>,
linux-fsdevel@...r.kernel.org, ocfs2-devel@....oracle.com,
Mark Fasheh <mfasheh@...e.com>,
"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH 09/27] fs: Push mnt_want_write() outside of i_mutex
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@....oracle.com
> CC: Mark Fasheh <mfasheh@...e.com>
> CC: Joel Becker <jlbec@...lplan.org>
> CC: "David S. Miller" <davem@...emloft.net>
> BugLink: https://bugs.launchpad.net/bugs/897421
> Tested-by: Kamal Mostafa <kamal@...onical.com>
> Tested-by: Peter M. Petrakis <peter.petrakis@...onical.com>
> Tested-by: Dann Frazier <dann.frazier@...onical.com>
> Tested-by: Massimo Morana <massimo.morana@...onical.com>
> Signed-off-by: Jan Kara <jack@...e.cz>
Acked-by: Joel Becker <jlbec@...lplan.org>
> ---
> 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@...lplan.org
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