On Thu 04-08-11 11:10:54, Miklos Szeredi wrote: > On Wed, 2011-08-03 at 23:17 +0100, Al Viro wrote: > > On Wed, Aug 03, 2011 at 12:48:39PM +0200, Miklos Szeredi wrote: > > > @@ -696,6 +696,11 @@ vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void > > > mnt->mnt_sb = root->d_sb; > > > mnt->mnt_mountpoint = mnt->mnt_root; > > > mnt->mnt_parent = mnt; > > > + > > > + br_write_lock(vfsmount_lock); > > > + list_add_tail(&mnt->mnt_instance, &mnt->mnt_sb->s_mounts); > > > + br_write_unlock(vfsmount_lock); > > > > Racy. > > > > > @@ -745,6 +750,10 @@ static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root, > > > if (!list_empty(&old->mnt_expire)) > > > list_add(&mnt->mnt_expire, &old->mnt_expire); > > > } > > > + > > > + br_write_lock(vfsmount_lock); > > > + list_add_tail(&mnt->mnt_instance, &mnt->mnt_sb->s_mounts); > > > + br_write_unlock(vfsmount_lock); > > > > Ditto. If you expect to be able to find *all* vfsmounts over given sb, > > this locking is simply wrong. > > I don't understand. All accesses to mnt_instance/s_mounts are protected > by vfsmount_lock. What else is needed? I guess Al meant that sb_prepare_remount_readonly() from the next patch could race with new mountpoint being added to the list and the check is thus still unreliable? Quickly checking the locking seems to confirm that since e.g. clone_mnt() does not hold s_umount semaphore (only namespace_sem?) and do_remount_sb() has it the other way around... Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
