linux-kernel - Re: [PATCH-block] blk-cgroup: Use css_tryget() in blkcg_destroy

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20221128140631.GI25160@blackbody.suse.cz>
Date:   Mon, 28 Nov 2022 15:06:31 +0100
From:   Michal Koutný <mkoutny@...e.com>
To:     Waiman Long <longman@...hat.com>
Cc:     Tejun Heo <tj@...nel.org>, Jens Axboe <axboe@...nel.dk>,
        cgroups@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, Ming Lei <ming.lei@...hat.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hillf Danton <hdanton@...a.com>, Yi Zhang <yi.zhang@...hat.com>
Subject: Re: [PATCH-block] blk-cgroup: Use css_tryget() in
 blkcg_destroy_blkgs()

Hello.

On Sun, Nov 27, 2022 at 10:30:57PM -0500, Waiman Long <longman@...hat.com> wrote:
> That may not be true if there is no blkg associated with the blkcg. If
> css_get() fails, the subsequent css_put() call may lead to data
> corruption as was illustrated in a test system that it crashed on
> bootup when that commit was included.

Do you have a stacktrace of the underflowing css_put() in
blkcg_destroy_blkgs()?

It looks to me slightly as a mistake of the caller site that it passes
struct blkcg * without any references.

By a cursory look, could it be cgwb_release_workfn?

--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -390,11 +390,11 @@ static void cgwb_release_workfn(struct work_struct *work)
        wb_shutdown(wb);

        css_put(wb->memcg_css);
-       css_put(wb->blkcg_css);
        mutex_unlock(&wb->bdi->cgwb_release_mutex);

        /* triggers blkg destruction if no online users left */
        blkcg_unpin_online(wb->blkcg_css);
+       css_put(wb->blkcg_css);

        fprop_local_destroy_percpu(&wb->memcg_completions);

Does your crash involve this stack?

Thanks,
Michal

Download attachment "signature.asc" of type "application/pgp-signature" (229 bytes)