linux-kernel - Re: WARNING: syz-executor still has locks held!

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Message-ID: <20190320132936.GB8696@dhcp22.suse.cz>
Date:   Wed, 20 Mar 2019 14:29:36 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     syzbot <syzbot+b70f2aabc707c69c9239@...kaller.appspotmail.com>,
        chanho.min@....com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, pavel@....cz,
        rafael.j.wysocki@...el.com, syzkaller-bugs@...glegroups.com,
        viro@...iv.linux.org.uk
Subject: Re: WARNING: syz-executor still has locks held!

On Wed 20-03-19 14:24:11, Oleg Nesterov wrote:
> On 03/20, Michal Hocko wrote:
> >
> > Yes we do hold the cgred mutex while calling freezable_schedule but why
> > are we getting a warning is not really clear to me. The task should be
> > hidden from the freezer so why do we warn at all?
> 
> try_to_freeze() calls debug_check_no_locks_held() and this makes sense.

Yes it does. But it already ignores PF_NOFREEZE tasks and I fail to see
why is PF_FREEZER_SKIP any different. Yes we know we are holding the
lock and we have discussed that left and right before the patch was
merged but it seems that skipping the task was the only viable option
to fix suspend issues as removing the cgred is way way too complicated.

That being said, I was arguing against the patch initially because it
was a hack but sometimes that is the only way viable path short term.
-- 
Michal Hocko
SUSE Labs