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Message-ID: <6df79609-90eb-2f59-7e86-3532ac309a7a@huawei.com>
Date: Tue, 17 Mar 2020 22:05:09 +0800
From: yangerkun <yangerkun@...wei.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>,
Jeff Layton <jlayton@...nel.org>
CC: NeilBrown <neilb@...e.de>,
kernel test robot <rong.a.chen@...el.com>,
LKML <linux-kernel@...r.kernel.org>, <lkp@...ts.01.org>,
Bruce Fields <bfields@...ldses.org>,
Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [locks] 6d390e4b5d: will-it-scale.per_process_ops -96.6%
regression
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@...nel.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
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