lkml.org 
[lkml]   [2010]   [Nov]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] fanotify: dont destroy mark when ignore mask is cleared
From
Date
On Tue, 2010-11-30 at 16:59 +0100, Lino Sanfilippo wrote:
> On Tue, Nov 30, 2010 at 01:16:35PM +0100, Lino Sanfilippo wrote:
>
> > I guess it is a question of safe vs racy. Yes it is safe, nothing will
> > explode or panic. But we might have a race between one task removing an
> > event type causing the mask to go to 0 and we should destroy the mark
> > and another task adding an event type. If it raced just right we might
> > destroy the mark after the second task added to it. I guess we really
> > need to serialize fsnotify_mark() per group to solve the race...
> >
> > Do you want to take a stab at fixing these things or should I?
> >
> > -Eric
>
> IMHO the right thing to serialize this would be to do
>
> LOCK(groups->mark_lock)
> - get the inode mark
> - set the marks mask
> - possibly destroy the mask
> UNLOCK(groups->mark_lock)
>
> But we cant do this since setting the marks mask requires the lock of the mark
> - which would mean an incorrect lock order according to fsnotify_add_mark():
>
> mark->lock
> group->mark_lock
> inode->i_lock
>
> What we could do very easily is use another mutex instead (use an existing one like the
> groups notification_mutex, or a completely new one) which is responsible for synchronising
> add_mark()/remove_mark().

I'd think a new per group mutex would be the right way to go. I'm not
sure how I feel about notification_mutex. I guess you can go ahead and
overload it and we can split it off later if someone finds it to be a
performance blocker.

-Eric




\
 
 \ /
  Last update: 2010-11-30 17:21    [W:0.073 / U:0.016 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site