From ea5b778a8b98c85a87d66bf844904f9c3802b869 Mon Sep 17 00:00:00 2001 From: David Howells Date: Fri, 14 Jan 2011 19:10:03 +0000 Subject: Unexport do_add_mount() and add in follow_automount(), not ->d_automount() Unexport do_add_mount() and make ->d_automount() return the vfsmount to be added rather than calling do_add_mount() itself. follow_automount() will then do the addition. This slightly complicates things as ->d_automount() normally wants to add the new vfsmount to an expiration list and start an expiration timer. The problem with that is that the vfsmount will be deleted if it has a refcount of 1 and the timer will not repeat if the expiration list is empty. To this end, we require the vfsmount to be returned from d_automount() with a refcount of (at least) 2. One of these refs will be dropped unconditionally. In addition, follow_automount() must get a 3rd ref around the call to do_add_mount() lest it eat a ref and return an error, leaving the mount we have open to being expired as we would otherwise have only 1 ref on it. d_automount() should also add the the vfsmount to the expiration list (by calling mnt_set_expiry()) and start the expiration timer before returning, if this mechanism is to be used. The vfsmount will be unlinked from the expiration list by follow_automount() if do_add_mount() fails. This patch also fixes the call to do_add_mount() for AFS to propagate the mount flags from the parent vfsmount. Signed-off-by: David Howells Signed-off-by: Al Viro --- fs/afs/mntpt.c | 25 ++++++------------------- fs/cifs/cifs_dfs_ref.c | 26 ++++++-------------------- fs/internal.h | 2 ++ fs/namei.c | 42 +++++++++++++++++++++++++++++++++++------- fs/namespace.c | 41 +++++++++++++++++++++++++++++++++-------- fs/nfs/namespace.c | 24 ++++-------------------- 6 files changed, 86 insertions(+), 74 deletions(-) (limited to 'fs') diff --git a/fs/afs/mntpt.c b/fs/afs/mntpt.c index d23b2e344a78..aa59184151d0 100644 --- a/fs/afs/mntpt.c +++ b/fs/afs/mntpt.c @@ -241,7 +241,6 @@ error_no_devname: struct vfsmount *afs_d_automount(struct path *path) { struct vfsmount *newmnt; - int err; _enter("{%s,%s}", path->mnt->mnt_devname, path->dentry->d_name.name); @@ -249,24 +248,12 @@ struct vfsmount *afs_d_automount(struct path *path) if (IS_ERR(newmnt)) return newmnt; - mntget(newmnt); - err = do_add_mount(newmnt, path, MNT_SHRINKABLE, &afs_vfsmounts); - switch (err) { - case 0: - queue_delayed_work(afs_wq, &afs_mntpt_expiry_timer, - afs_mntpt_expiry_timeout * HZ); - _leave(" = %p {%s}", newmnt, newmnt->mnt_devname); - return newmnt; - case -EBUSY: - /* someone else made a mount here whilst we were busy */ - mntput(newmnt); - _leave(" = NULL [EBUSY]"); - return NULL; - default: - mntput(newmnt); - _leave(" = %d", err); - return ERR_PTR(err); - } + mntget(newmnt); /* prevent immediate expiration */ + mnt_set_expiry(newmnt, &afs_vfsmounts); + queue_delayed_work(afs_wq, &afs_mntpt_expiry_timer, + afs_mntpt_expiry_timeout * HZ); + _leave(" = %p {%s}", newmnt, newmnt->mnt_devname); + return newmnt; } /* diff --git a/fs/cifs/cifs_dfs_ref.c b/fs/cifs/cifs_dfs_ref.c index 0fc163808de3..7ed36536e754 100644 --- a/fs/cifs/cifs_dfs_ref.c +++ b/fs/cifs/cifs_dfs_ref.c @@ -351,7 +351,6 @@ free_xid: struct vfsmount *cifs_dfs_d_automount(struct path *path) { struct vfsmount *newmnt; - int err; cFYI(1, "in %s", __func__); @@ -361,25 +360,12 @@ struct vfsmount *cifs_dfs_d_automount(struct path *path) return newmnt; } - mntget(newmnt); - err = do_add_mount(newmnt, path, path->mnt->mnt_flags | MNT_SHRINKABLE, - &cifs_dfs_automount_list); - switch (err) { - case 0: - schedule_delayed_work(&cifs_dfs_automount_task, - cifs_dfs_mountpoint_expiry_timeout); - cFYI(1, "leaving %s [ok]" , __func__); - return newmnt; - case -EBUSY: - /* someone else made a mount here whilst we were busy */ - mntput(newmnt); - cFYI(1, "leaving %s [EBUSY]" , __func__); - return NULL; - default: - mntput(newmnt); - cFYI(1, "leaving %s [error %d]" , __func__, err); - return ERR_PTR(err); - } + mntget(newmnt); /* prevent immediate expiration */ + mnt_set_expiry(newmnt, &cifs_dfs_automount_list); + schedule_delayed_work(&cifs_dfs_automount_task, + cifs_dfs_mountpoint_expiry_timeout); + cFYI(1, "leaving %s [ok]" , __func__); + return newmnt; } const struct inode_operations cifs_dfs_referral_inode_operations = { diff --git a/fs/internal.h b/fs/internal.h index 9687c2ee2735..4931060fd089 100644 --- a/fs/internal.h +++ b/fs/internal.h @@ -70,6 +70,8 @@ extern void mnt_set_mountpoint(struct vfsmount *, struct dentry *, extern void release_mounts(struct list_head *); extern void umount_tree(struct vfsmount *, int, struct list_head *); extern struct vfsmount *copy_tree(struct vfsmount *, struct dentry *, int); +extern int do_add_mount(struct vfsmount *, struct path *, int); +extern void mnt_clear_expiry(struct vfsmount *); extern void __init mnt_init(void); diff --git a/fs/namei.c b/fs/namei.c index 5c89695ae1e4..c2e37727e3ab 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -900,6 +900,7 @@ static int follow_automount(struct path *path, unsigned flags, bool *need_mntput) { struct vfsmount *mnt; + int err; if (!path->dentry->d_op || !path->dentry->d_op->d_automount) return -EREMOTE; @@ -942,22 +943,49 @@ static int follow_automount(struct path *path, unsigned flags, return -EREMOTE; return PTR_ERR(mnt); } + if (!mnt) /* mount collision */ return 0; + /* The new mount record should have at least 2 refs to prevent it being + * expired before we get a chance to add it + */ + BUG_ON(mnt_get_count(mnt) < 2); + if (mnt->mnt_sb == path->mnt->mnt_sb && mnt->mnt_root == path->dentry) { + mnt_clear_expiry(mnt); + mntput(mnt); mntput(mnt); return -ELOOP; } - dput(path->dentry); - if (*need_mntput) - mntput(path->mnt); - path->mnt = mnt; - path->dentry = dget(mnt->mnt_root); - *need_mntput = true; - return 0; + /* We need to add the mountpoint to the parent. The filesystem may + * have placed it on an expiry list, and so we need to make sure it + * won't be expired under us if do_add_mount() fails (do_add_mount() + * will eat a reference unconditionally). + */ + mntget(mnt); + err = do_add_mount(mnt, path, path->mnt->mnt_flags | MNT_SHRINKABLE); + switch (err) { + case -EBUSY: + /* Someone else made a mount here whilst we were busy */ + err = 0; + default: + mnt_clear_expiry(mnt); + mntput(mnt); + mntput(mnt); + return err; + case 0: + mntput(mnt); + dput(path->dentry); + if (*need_mntput) + mntput(path->mnt); + path->mnt = mnt; + path->dentry = dget(mnt->mnt_root); + *need_mntput = true; + return 0; + } } /* diff --git a/fs/namespace.c b/fs/namespace.c index d94ccd6ddafd..bfcb701f9490 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1925,15 +1925,14 @@ static int do_new_mount(struct path *path, char *type, int flags, if (IS_ERR(mnt)) return PTR_ERR(mnt); - return do_add_mount(mnt, path, mnt_flags, NULL); + return do_add_mount(mnt, path, mnt_flags); } /* * add a mount into a namespace's mount tree - * - provide the option of adding the new mount to an expiration list + * - this unconditionally eats one of the caller's references to newmnt. */ -int do_add_mount(struct vfsmount *newmnt, struct path *path, - int mnt_flags, struct list_head *fslist) +int do_add_mount(struct vfsmount *newmnt, struct path *path, int mnt_flags) { int err; @@ -1963,9 +1962,6 @@ int do_add_mount(struct vfsmount *newmnt, struct path *path, if ((err = graft_tree(newmnt, path))) goto unlock; - if (fslist) /* add to the specified expiration list */ - list_add_tail(&newmnt->mnt_expire, fslist); - up_write(&namespace_sem); return 0; @@ -1975,7 +1971,36 @@ unlock: return err; } -EXPORT_SYMBOL_GPL(do_add_mount); +/** + * mnt_set_expiry - Put a mount on an expiration list + * @mnt: The mount to list. + * @expiry_list: The list to add the mount to. + */ +void mnt_set_expiry(struct vfsmount *mnt, struct list_head *expiry_list) +{ + down_write(&namespace_sem); + br_write_lock(vfsmount_lock); + + list_add_tail(&mnt->mnt_expire, expiry_list); + + br_write_unlock(vfsmount_lock); + up_write(&namespace_sem); +} +EXPORT_SYMBOL(mnt_set_expiry); + +/* + * Remove a vfsmount from any expiration list it may be on + */ +void mnt_clear_expiry(struct vfsmount *mnt) +{ + if (!list_empty(&mnt->mnt_expire)) { + down_write(&namespace_sem); + br_write_lock(vfsmount_lock); + list_del_init(&mnt->mnt_expire); + br_write_unlock(vfsmount_lock); + up_write(&namespace_sem); + } +} /* * process a list of expirable mountpoints with the intent of discarding any diff --git a/fs/nfs/namespace.c b/fs/nfs/namespace.c index f3fbb1bf3f18..f32b8603dca8 100644 --- a/fs/nfs/namespace.c +++ b/fs/nfs/namespace.c @@ -149,26 +149,10 @@ struct vfsmount *nfs_d_automount(struct path *path) if (IS_ERR(mnt)) goto out; - mntget(mnt); - err = do_add_mount(mnt, path, path->mnt->mnt_flags | MNT_SHRINKABLE, - &nfs_automount_list); - switch (err) { - case 0: - dprintk("%s: done, success\n", __func__); - schedule_delayed_work(&nfs_automount_task, nfs_mountpoint_expiry_timeout); - break; - case -EBUSY: - /* someone else made a mount here whilst we were busy */ - mntput(mnt); - dprintk("%s: done, collision\n", __func__); - mnt = NULL; - break; - default: - mntput(mnt); - dprintk("%s: done, error %d\n", __func__, err); - mnt = ERR_PTR(err); - break; - } + dprintk("%s: done, success\n", __func__); + mntget(mnt); /* prevent immediate expiration */ + mnt_set_expiry(mnt, &nfs_automount_list); + schedule_delayed_work(&nfs_automount_task, nfs_mountpoint_expiry_timeout); out: nfs_free_fattr(fattr); -- cgit v1.2.3-58-ga151