On Thu, Nov 10, 2016 at 9:46 PM, Jan Kara <j...@suse.cz> 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. */
