linux-kernel - Re: [PATCH] f2fs: move f2fs to use reader-unfair rwsems

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: <a23a3226-95d9-9835-c1c7-2d13f4a1ee16@redhat.com>
Date:   Mon, 10 Jan 2022 11:18:27 -0500
From:   Waiman Long <longman@...hat.com>
To:     Christoph Hellwig <hch@...radead.org>,
        Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        Tim Murray <timmurray@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>
Subject: Re: [PATCH] f2fs: move f2fs to use reader-unfair rwsems


On 1/10/22 03:05, Christoph Hellwig wrote:
> Adding the locking primitive maintainers to this patch adding open coded
> locking primitives..
>
> On Sat, Jan 08, 2022 at 08:46:17AM -0800, Jaegeuk Kim wrote:
>> From: Tim Murray <timmurray@...gle.com>
>>
>> f2fs rw_semaphores work better if writers can starve readers,
>> especially for the checkpoint thread, because writers are strictly
>> more important than reader threads. This prevents significant priority
>> inversion between low-priority readers that blocked while trying to
>> acquire the read lock and a second acquisition of the write lock that
>> might be blocking high priority work.
>>
>> Signed-off-by: Tim Murray <timmurray@...gle.com>
>> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>

We could certainly implement a down_read() variant (e.g. 
down_read_lowprio()) with its own slowpath function to do this within 
the rwsem code as long as there is a good use-case for this kind of 
functionality.

Cheers,
Longman