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

[Jan Kara]

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?

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