Re: Reproducible, long-standing fanotify+autofs problem

[Jan Kara <jack@suse.cz>]

On Wed 25-01-17 16:54:46, Amir Goldstein wrote:
> On Wed, Jan 25, 2017 at 4:42 PM, Marko Rauhamaa
> <marko.rauhamaa@f-secure.com> wrote:
> > Amir Goldstein <amir73il@gmail.com>:
> >
> >> On Wed, Jan 25, 2017 at 4:06 PM, Marko Rauhamaa
> >> <marko.rauhamaa@f-secure.com> wrote:
> >>> Amir Goldstein <amir73il@gmail.com>:
> >> So I am confused.
> >> Your test program sets a watch on permission events on the mount
> >> and does not respond to permission events on the mount, so all
> >> file system operations on the mount SHOULD be blocked.
> >> What am I missing?
> >
> > The problem is that the fanotify_mark() system call is hanging and as a
> > side effect blocks everything.
> >
> > The side effect is probably completely understandable, but
> > fanotify_mark() should never hang, should it?
> >
> >
> 
> I see. I guess it shouldn't block.
> Also with this understanding, I am not sure Jan's work is relevant to
> your issue.

Yeah, it should not, although I expect this is some weird interaction with
autofs which tries to open something, which generates fanotify open event
for already created mark and thus following mark creation gets hung. Can
you reproduce the hang and send contents of dmesg after you do
'echo t >/proc/sysrq-trigger'? Thanks.

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