linux-kernel - Re: Fwd: trinity test fanotify cause hungtasks on kernel 4.13

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Date:   Fri, 28 Jul 2017 09:45:09 +0200
From:   Jan Kara <jack@...e.cz>
To:     Gu Zheng <guzheng1@...wei.com>
Cc:     eparis@...hat.com, viro@...iv.linux.org.uk,
        Jan Kara <jack@...e.cz>, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "miaoxie@...wei.com" <miaoxie@...wei.com>
Subject: Re: Fwd: trinity test fanotify cause hungtasks on kernel 4.13

On Fri 28-07-17 11:52:13, Gu Zheng wrote:
> 
> hi,ALL:
> when we used the trinity test the fanotify interfaces, it cause many hungtasks.
> CONFIG_FANOTIFY_ACCESS_PERMISSIONS=y
> the shell is  simple:
>   1 #!/bin/bash
>   2
>   3 while true
>   4 do
>   5 ./trinity -c fanotify_init -l off -C 2 -X > /dev/null 2>&1 &
>   6 sleep 1
>   7 ./trinity -c fanotify_mark -l off -C 2 -X > /dev/null 2>&1 &
>   8 sleep 10
>   9 done
> we found the trinity enter the D state fastly.
> we check the pids'stack

<snip>

> all progresses are waiting for the response in fanotify_handle_event->fanotify_get_response,
> becauseof non-response or killed monitor,so the waitqueue is  in blocked state,
> then the others will be stucked which use the  fanotify_get_response.

Yes, this all works as expected.

> if we use wait_event_timeout , the responed time can not be guaranteed.
> 
> do you have any ideas?

So if your target is sensible trinity testing of fanotify, what you could
do is that you would gather all descriptors where fanotify_init()
succeeded, watch them and reply to all fanotify events. Alternatively you
could just close these descriptors - that would tear down fanotify instance
and all events will be auto-accepted.

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