On Mon, Sep 24, 2012 at 4:23 AM, Herbert Poetzl <herbert@xxxxxxxxxxxx> wrote:
>
> currently we do:
>
> br_read_lock(&vfsmount_lock);
> root = current->fs->root;
> root_mnt = real_mount(root.mnt);
> point = root.dentry;
>
> while ((mnt != mnt->mnt_parent) && (mnt != root_mnt)) {
> point = mnt->mnt_mountpoint;
> mnt = mnt->mnt_parent;
> }
>
> ret = (mnt == root_mnt) && is_subdir(point, root.dentry);
> br_read_unlock(&vfsmount_lock);
>
> and we have been considering to move the br_read_unlock()
> right before the is_subdir() call
So the read lock itself should not cause problems. We have tons of
high-frequency read-lockers, over quite big areas.
But exactly because the readlockers are so high-frequency, I'd expect
any problems to be *found* by read-lockers.
But the *cause* would likely be
- missing unlocks
- write-locks
- recursion on the locks (including read-locks: they are actually
per-cpu spinlocks)
but I'd have expected lockdep to find anything obvious like that.
If the locking itself is fine, maybe the loop above (or the
is_subdir()) is infinite due to mnt->mnt_parent somehow becoming a
circular loop. Maybe due to corrupt data structures traversed inside
the lock, causing infinite loops..
I really don't know the vserver patches, it would be much more
interesting if you can recreate the problems using a standard kernel.
Linus
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