On Wed, Feb 1, 2017 at 12:44 PM, Jan Kara <jack@xxxxxxx> 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@xxxxxxx> > --- 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@xxxxxxxxx>
