Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [locks] 6d390e4b5d: will-it-scale.per_process_ops -96.6%
 regression
From:   yangerkun <yangerkun@huawei.com>
To:     Linus Torvalds <torvalds@linux-foundation.org>,
        Jeff Layton <jlayton@kernel.org>
CC:     NeilBrown <neilb@suse.de>,
        kernel test robot <rong.a.chen@intel.com>,
        LKML <linux-kernel@vger.kernel.org>, <lkp@lists.01.org>,
        Bruce Fields <bfields@fieldses.org>,
        Al Viro <viro@zeniv.linux.org.uk>
References: <20200308140314.GQ5972@shao2-debian>
 <875zfbvrbm.fsf@notabene.neil.brown.name>
 <CAHk-=wg8N4fDRC3M21QJokoU+TQrdnv7HqoaFW-Z-ZT8z_Bi7Q@mail.gmail.com>
 <0066a9f150a55c13fcc750f6e657deae4ebdef97.camel@kernel.org>
 <CAHk-=whUgeZGcs5YAfZa07BYKNDCNO=xr4wT6JLATJTpX0bjGg@mail.gmail.com>
 <87v9nattul.fsf@notabene.neil.brown.name>
 <CAHk-=wiNoAk8v3GrbK3=q6KRBrhLrTafTmWmAo6-up6Ce9fp6A@mail.gmail.com>
 <87o8t2tc9s.fsf@notabene.neil.brown.name>
 <CAHk-=wj5jOYxjZSUNu_jdJ0zafRS66wcD-4H0vpQS=a14rS8jw@mail.gmail.com>
 <f000e352d9e103b3ade3506aac225920420d2323.camel@kernel.org>
 <877dznu0pk.fsf@notabene.neil.brown.name>
 <CAHk-=whYQqtW6B7oPmPr9-PXwyqUneF4sSFE+o3=7QcENstE-g@mail.gmail.com>
 <b5a1bb4c4494a370f915af479bcdf8b3b351eb6d.camel@kernel.org>
 <87pndcsxc6.fsf@notabene.neil.brown.name>
 <ce48ed9e48eda3c0f27d2f417314bd00cb1a68db.camel@kernel.org>
 <CAHk-=whnqDS0NJtAaArVeYQz3hcU=4Ja3auB1Jvs42eADfUgMQ@mail.gmail.com>
 <7c8d3752-6573-ab83-d0af-f3dd4fc373f5@huawei.com>
Message-ID: <6df79609-90eb-2f59-7e86-3532ac309a7a@huawei.com>
Date:   Tue, 17 Mar 2020 22:05:09 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101
 Thunderbird/60.7.0
MIME-Version: 1.0
In-Reply-To: <7c8d3752-6573-ab83-d0af-f3dd4fc373f5@huawei.com>
Content-Type: text/plain; charset="utf-8"; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


On 2020/3/17 9:41, yangerkun wrote:
> 
> 
> On 2020/3/17 1:26, Linus Torvalds wrote:
>> On Mon, Mar 16, 2020 at 4:07 AM Jeff Layton <jlayton@kernel.org> wrote:
>>>
>>>
>>> +       /*
>>> +        * If fl_blocker is NULL, it won't be set again as this 
>>> thread "owns"
>>> +        * the lock and is the only one that might try to claim the 
>>> lock.
>>> +        * Because fl_blocker is explicitly set last during a delete, 
>>> it's
>>> +        * safe to locklessly test to see if it's NULL. If it is, 
>>> then we know
>>> +        * that no new locks can be inserted into its 
>>> fl_blocked_requests list,
>>> +        * and we can therefore avoid doing anything further as long 
>>> as that
>>> +        * list is empty.
>>> +        */
>>> +       if (!smp_load_acquire(&waiter->fl_blocker) &&
>>> +           list_empty(&waiter->fl_blocked_requests))
>>> +               return status;
>>
>> Ack. This looks sane to me now.
>>
>> yangerkun - how did you find the original problem?\
> 
> While try to fix CVE-2019-19769, add some log in __locks_wake_up_blocks 
> help me to rebuild the problem soon. This help me to discern the problem 
> soon.
> 
>>
>> Would you mind using whatever stress test that caused commit
>> 6d390e4b5d48 ("locks: fix a potential use-after-free problem when
>> wakeup a waiter") with this patch? And if you did it analytically,
>> you're a champ and should look at this patch too!
> 
> I will try to understand this patch, and if it's looks good to me, will 
> do the performance test!

This patch looks good to me, with this patch, the bug '6d390e4b5d48 
("locks: fix a potential use-after-free problem when wakeup a waiter")' 
describes won't happen again. Actually, I find that syzkaller has report 
this bug before[1], and the log of it can help us to reproduce it with 
some latency in __locks_wake_up_blocks!

Also, some ltp testcases describes in [2] pass too with the patch!

For performance test, I have try to understand will-it-scale/lkp, but it 
seem a little complex to me, and may need some more time. So, Rong Chen, 
can you help to do this? Or the results may come a little later...

Thanks,
----
[1] https://syzkaller.appspot.com/bug?extid=922689db06e57b69c240
[2] https://lkml.org/lkml/2020/3/11/578