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

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Message-ID: <20190320132410.GB21673@redhat.com>
Date:   Wed, 20 Mar 2019 14:24:11 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>
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 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.

Another task can sleep waiting for the same lock; in this case
try_to_freeze_tasks() will fail but it won't blame the lock holder exactly
because it is "hidden from the freezer".

Oleg.