linux-kernel - Re: [PATCH v6 0/6] lockinig/rwsem: Fix rwsem bugs & enable true lock handoff

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: <f00bff72-c923-2552-f181-f1bcc034bff9@redhat.com>
Date:   Mon, 23 Jan 2023 16:10:02 -0500
From:   Waiman Long <longman@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        linux-kernel@...r.kernel.org, john.p.donnelly@...cle.com,
        Hillf Danton <hdanton@...a.com>,
        Mukesh Ojha <quic_mojha@...cinc.com>,
        Ting11 Wang 王婷 <wangting11@...omi.com>
Subject: Re: [PATCH v6 0/6] lockinig/rwsem: Fix rwsem bugs & enable true lock
 handoff

On 1/22/23 22:40, Waiman Long wrote:
>
> On 1/22/23 08:46, Peter Zijlstra wrote:
>> On Thu, Nov 17, 2022 at 09:20:10PM -0500, Waiman Long wrote:
>>
>>> Waiman Long (6):
>>>    locking/rwsem: Prevent non-first waiter from spinning in 
>>> down_write() slowpath
>>>    locking/rwsem: Disable preemption at all down_read*() and 
>>> up_read() code paths
>>>    locking/rwsem: Disable preemption at all down_write*() and 
>>> up_write() code paths
>>>    locking/rwsem: Change waiter->hanodff_set to a handoff_state enum
>> After all these we still have down_read_non_owner() using
>> __rwsem_set_reader_owner() outside of the preempt_disable() region.
>>
>> Now, let me go stare at this one:
>
> Thanks for spotting that. I kind of overlook the fact we have a 
> down_read_non_owner(). Will update that as well.

After looking further into this, we will need to either pass one more 
parameter to __down_read() for this special case or to do 
preempt_disable/enable in each of the higher level down_read functions. 
As down_read_non_owner() is a rarely called function, I doubt it is 
worth the extra effort to do that since the owner value (other than the 
RWSEM_READER_OWNED bit) is for debugging purpose only and is not 
critical to the correct functioning of a rwsem. I will add a comment to 
note that.

Cheers,
Longman