Re: [PATCH 06/25] fsnotify: Attach marks to object via dedicated head structure

[Amir Goldstein <amir73il@gmail.com>]

On Wed, Feb 1, 2017 at 12:44 PM, Jan Kara <jack@suse.cz> wrote:
> Currently notification marks are attached to object (inode or vfsmnt) by
> a hlist_head in the object. The list is also protected by a spinlock in
> the object. So while there is any mark attached to the list of marks,
> the object must be pinned in memory (and thus e.g. last iput() deleting
> inode cannot happen). Also for list iteration in fsnotify() to work, we
> must hold fsnotify_mark_srcu lock so that mark itself and
> mark->obj_list.next cannot get freed. Thus we are required to wait for
> response to fanotify events from userspace process with
> fsnotify_mark_srcu lock held. That causes issues when userspace process
> is buggy and does not reply to some event - basically the whole
> notification subsystem gets eventually stuck.
>
> So to be able to drop fsnotify_mark_srcu lock while waiting for
> response, we have to pin the mark in memory and make sure it stays in
> the object list (as removing the mark waiting for response could lead to
> lost notification events for groups later in the list). However we don't
> want inode reclaim to block on such mark as that would lead to system
> just locking up elsewhere.
>
> This commit tries to pave a way towards solving these conflicting
> lifetime needs. Instead of anchoring the list of marks directly in the
> object, we anchor it in a dedicated structure (fsnotify_mark_connector)
> and just point to that structure from the object. In the following patch
> we will also protect the list by a spinlock contained in that structure.
> With this, we will be able to detach notification marks from object
> without having to modify the list itself.
>
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---

The patch split was useful for review on one hand, but it generated some weird
looking functions like fsnotify_destroy_marks() and grab_connector(), which
whose name does not accurately reflect what they do in the context of
this patch.
However, since those are totally reshuffled in next patches, you may re-add

Reviewed-by: Amir Goldstein <amir73il@gmail.com>