[lkml]   [2016]   [Nov]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: fsnotify_mark_srcu wtf?
On Thu, Nov 10, 2016 at 9:46 PM, Jan Kara <> wrote:


> Well but how would you like to protect the mark list hanging off the inode
> / mountpoint with two SRCUs? You'd need two lists hanging off the inode &
> mountpoint (for different priorities) and that's too big cost to pay to
> accomodate broken userspace...

This is the plan.
I have a rough implementation, which still requires some testing:

* fsnotify_perm_mark[1] protects reads of the first half of inode/vfsmount
* mark lists, which consist of the high priority (>0) marks, whose masks
* may contain permission events.
* fsnotify_perm_mark[0] protects reads of the second half of inode/vfsmount
* mark lists, which consist of the low priority (0) marks, whose masks
* do not contain permission events.
* High priority marks and low priority marks are added to different
* destroy lists and freed by different reapers, who synchronize only
* the relevant srcu.
* Before traversing to first mark on the list we must hold both srcu.
* While traversing first half, we may temporary drop fsnotify_perm_mark[0]
* to handle a blocking permission event.
* When we reach the first low level mark, we may drop fsnotify_perm_mark[1]
* for good.

 \ /
  Last update: 2016-11-13 19:44    [W:0.129 / U:13.280 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site