diff options
author | Dave Hansen <haveblue@us.ibm.com> | 2008-02-15 14:37:48 -0800 |
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committer | Al Viro <viro@zeniv.linux.org.uk> | 2008-04-19 00:29:25 -0400 |
commit | 4a3fd211ccfc08a88edc824300e25a87785c6a5f (patch) | |
tree | 99f1a76a99fa78464b8de731f7fdb5bcc9667a5e /fs/open.c | |
parent | 42a74f206b914db13ee1f5ae932dcd91a77c8579 (diff) | |
download | linux-stable-4a3fd211ccfc08a88edc824300e25a87785c6a5f.tar.gz |
[PATCH] r/o bind mounts: elevate write count for open()s
This is the first really tricky patch in the series. It elevates the writer
count on a mount each time a non-special file is opened for write.
We used to do this in may_open(), but Miklos pointed out that __dentry_open()
is used as well to create filps. This will cover even those cases, while a
call in may_open() would not have.
There is also an elevated count around the vfs_create() call in open_namei().
See the comments for more details, but we need this to fix a 'create, remount,
fail r/w open()' race.
Some filesystems forego the use of normal vfs calls to create
struct files. Make sure that these users elevate the mnt
writer count because they will get __fput(), and we need
to make sure they're balanced.
Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs/open.c')
-rw-r--r-- | fs/open.c | 36 |
1 files changed, 34 insertions, 2 deletions
diff --git a/fs/open.c b/fs/open.c index 8111947905d8..e12f17010324 100644 --- a/fs/open.c +++ b/fs/open.c @@ -730,6 +730,35 @@ out: return error; } +/* + * You have to be very careful that these write + * counts get cleaned up in error cases and + * upon __fput(). This should probably never + * be called outside of __dentry_open(). + */ +static inline int __get_file_write_access(struct inode *inode, + struct vfsmount *mnt) +{ + int error; + error = get_write_access(inode); + if (error) + return error; + /* + * Do not take mount writer counts on + * special files since no writes to + * the mount itself will occur. + */ + if (!special_file(inode->i_mode)) { + /* + * Balanced in __fput() + */ + error = mnt_want_write(mnt); + if (error) + put_write_access(inode); + } + return error; +} + static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt, int flags, struct file *f, int (*open)(struct inode *, struct file *)) @@ -742,7 +771,7 @@ static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt, FMODE_PREAD | FMODE_PWRITE; inode = dentry->d_inode; if (f->f_mode & FMODE_WRITE) { - error = get_write_access(inode); + error = __get_file_write_access(inode, mnt); if (error) goto cleanup_file; } @@ -784,8 +813,11 @@ static struct file *__dentry_open(struct dentry *dentry, struct vfsmount *mnt, cleanup_all: fops_put(f->f_op); - if (f->f_mode & FMODE_WRITE) + if (f->f_mode & FMODE_WRITE) { put_write_access(inode); + if (!special_file(inode->i_mode)) + mnt_drop_write(mnt); + } file_kill(f); f->f_path.dentry = NULL; f->f_path.mnt = NULL; |