[LTP] [PATCH v2] inotify: Add test for inotify mark destruction race

[Jan Kara]

On Thu 14-04-16 16:14:25, Xiaoguang Wang wrote:
> On 04/14/2016 04:15 PM, Jan Kara wrote:
> > Hello,
> > 
> > On Thu 14-04-16 10:06:59, Xiaoguang Wang wrote:
> >> On 08/25/2015 07:29 PM, Cyril Hrubis wrote:
> >>> Hi!
> >>>> Interesting, probably SRCU is much slower with this older kernel. From my
> >>>> experiments 100 iterations isn't quite reliable to trigger the oops in my
> >>>> testing instance. But 400 seem to be good enough.
> >>>
> >>> I've changed the nuber of iterations to 400 and pushed it to git,
> >>> thanks.
> >>>
> >>
> >> In upstream kernel v4.6-rc3-17-g1c74a7f and RHEL7.2GA, I sometimes get such
> >> error:
> >> ---------------------------------------------------------------------------
> >> inotify06    1  TBROK  :  inotify06.c:104: inotify_init failed: errno=EMFILE(24): Too many open files
> >> inotify06    2  TBROK  :  inotify06.c:104: Remaining cases broken
> >> ---------------------------------------------------------------------------
> >> But look at the inotify06.c, inotify_fd is closed every iteration.
> >> For normal file descriptors, "close(fd) succeeds" does not mean related kernel
> >> resources have been released immediately(processes may still reference fd).
> >>
> >> Then inotify_fd  also has similar behavior? Even close(inotify_fd) returns,
> >> that does not mean the number of current inotify instances have decreased one
> >> immediately, then later inotify_init() calls may exceeds the /proc/sys/fs/inotify/max_user_instances and
> >> return EMFILE error?  I had added some debug code in kernel, it seems that close(inotify_fd)
> >> does not make sure current inotify instances decreases one immediately.
> >>
> >> So I'd like to know this is expected behavior for inotify? If yes, we can
> >> echo 400 > /proc/sys/fs/inotify/max_user_instances to avoid EMFILE error.
> >> If not, this is a kernel bug?
> > 
> > Interesting, I've never seen this. Number of inotify instances is maintaned
> > immediately - i.e., it is dropped as soon as the last descriptor pointing to
> > the instance is closed. So I'm not sure how what you describe can happen.
> > How do you reproduce the issue?
> I just call ./inotify06 directly, and about 50% chance, it'll fail(return EMFILE).

Hum, I've just tried 4.6-rc1 which I have running on one test machine and
it survives hundreds of inotify06 calls in a loop without issues. I have
max_user_instances set to 128 on that machine... So I suspect the problem
is somewhere in your exact userspace setup. Aren't there other processes
using inotify heavily for that user?

								Honza
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR