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fs: Push mnt_want_write() outside of i_mutex 

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.

[AV: scratch the previous, mnt_want_write() has been moved to kern_path_create()
by now]

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Jan Kara 2012-06-12 16:20:30 +02:00 committed by Al Viro
parent 4fcf1c6205
commit c30dabfe5d
1 changed files with 25 additions and 21 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

46
fs/namei.c
View File

@ -2975,6 +2975,7 @@ struct dentry *kern_path_create(int dfd, const char *pathname, struct path *path
{
struct dentry *dentry = ERR_PTR(-EEXIST);
struct nameidata nd;
int err2;
int error = do_path_lookup(dfd, pathname, LOOKUP_PARENT, &nd);
if (error)
return ERR_PTR(error);
@ -2988,6 +2989,8 @@ struct dentry *kern_path_create(int dfd, const char *pathname, struct path *path
nd.flags &= ~LOOKUP_PARENT;
nd.flags |= LOOKUP_CREATE | LOOKUP_EXCL;
/* don't fail immediately if it's r/o, at least try to report other errors */
err2 = mnt_want_write(nd.path.mnt);
/*
* Do the final lookup.
*/
@ -3009,9 +3012,10 @@ struct dentry *kern_path_create(int dfd, const char *pathname, struct path *path
error = -ENOENT;
goto fail;
}
error = mnt_want_write(nd.path.mnt);
if (error)
if (unlikely(err2)) {
error = err2;
goto fail;
}
*path = nd.path;
return dentry;
fail:
@ -3019,6 +3023,8 @@ fail:
dentry = ERR_PTR(error);
unlock:
mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
if (!err2)
mnt_drop_write(nd.path.mnt);
out:
path_put(&nd.path);
return dentry;
@ -3266,6 +3272,9 @@ 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);
@ -3276,19 +3285,15 @@ 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);
@ -3355,6 +3360,9 @@ 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);
@ -3367,21 +3375,17 @@ 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);
@ -3753,6 +3757,10 @@ 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;
@ -3788,23 +3796,19 @@ 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);