Re: Inotify problem [was Re: 2.6.13-rc6-mm1]

[John McCutchan <ttb@tentacle.dhs.org>]

On Thu, 2005-08-25 at 11:54 -0700, George Anzinger wrote:
> Robert Love wrote:
> > On Thu, 2005-08-25 at 09:33 -0400, John McCutchan wrote:
> > 
> >>On Thu, 2005-08-25 at 22:07 +1200, Reuben Farrelly wrote:
> >>
> ~
> >>>dovecot: Aug 25 19:31:26 Warning: IMAP(gilly): removing wd 1022 from inotify fd 4
> >>>dovecot: Aug 25 19:31:27 Warning: IMAP(gilly): inotify_add_watch returned 1023
> >>>dovecot: Aug 25 19:31:27 Warning: IMAP(gilly): inotify_add_watch returned 1024
> >>>dovecot: Aug 25 19:31:27 Warning: IMAP(gilly): removing wd 1024 from inotify fd 4
> >>>dovecot: Aug 25 19:31:27 Error: IMAP(gilly): inotify_rm_watch() failed: 
> >>>Invalid argument
> >>>dovecot: Aug 25 19:31:27 Warning: IMAP(gilly): removing wd 1023 from inotify fd 4
> >>>dovecot: Aug 25 19:31:28 Warning: IMAP(gilly): inotify_add_watch returned 1024
> >>>dovecot: Aug 25 19:31:28 Warning: IMAP(gilly): inotify_add_watch returned 1024
> >>>
> >>>Note the incrementing wd value even though we are removing them as we go..
> >>>
> >>
> >>What kernel are you running? The wd's should ALWAYS be incrementing, you
> >>should never get the same wd as you did before. From your log, you are
> >>getting the same wd (after you inotify_rm_watch it). I can reproduce
> >>this bug on 2.6.13-rc7.
> >>
> >>idr_get_new_above 
> >>
> >>isn't returning something above.
> >>
> >>Also, the idr layer seems to be breaking when we pass in 1024. I can
> >>reproduce that on my 2.6.13-rc7 system as well.
> >>
> >>
> >>>This is using latest CVS of dovecot code and with 2.6.12-rc6-mm(1|2) kernel.
> >>>
> >>>Robert, John, what do you think?   Is this possibly related to the oops seen 
> >>>in the log that I reported earlier?  (Which is still showing up 2-3 times per 
> >>>day, btw)
> >>
> >>There is definitely something broken here.
> > 
> > 
> > Jim, George-
> > 
> > We are seeing a problem in the idr layer.  If we do idr_find(1024) when,
> > say, a low valued idr, like, zero, is unallocated, NULL is returned.
> 
> I think the best thing is to take idr into user space and emulate the 
> problem usage.  To this end, from the log it appears that you _might_ be 
> moving between 0, 1 and 2 entries increasing the number each time.  It 
> also appears that the failure happens here:
> add 1023
> add 1024
> find 1024  or is it the remove that fails?  It also looks like 1024 got 
> allocated twice.  Am I reading the log correctly?

You are reading the log correctly. There are two bugs. One is that if we
pass X to idr_get_new_above, it can return X again (doesn't ever seem to
return < X). The other problem is that the find fails on 1024 (and 2048
if we skip 1024).

> 
> So, is it correct to assume that the tree is empty save these two at 
> this time?  I am just trying to figure out what the test program needs 
> to do.

Yes that is the exact scenario. Only 2 id's are used at any given time,
and once we hit 1024 things break. This doesn't happen when the tree is
not empty.

Thanks for looking at this!
-- 
John McCutchan <ttb@tentacle.dhs.org>