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Message-ID: <20120417074355.GA7198@quack.suse.cz>
Date: Tue, 17 Apr 2012 09:43:55 +0200
From: Jan Kara <jack@...e.cz>
To: Joel Becker <jlbec@...lplan.org>
Cc: Jan Kara <jack@...e.cz>, 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 16-04-12 19:18:53, Joel Becker wrote:
> 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>
Thanks. Added.
Honza
>
> > ---
> > 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
--
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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