linux-kernel - Re: [PATCH] pstore: Revert pmsg

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: <CAEXW_YQY64XdhuxYuwqBkeYQFKTt4yDyHwUfBip4hf+A83mL-g@mail.gmail.com>
Date:   Tue, 7 Mar 2023 15:19:23 -0500
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        John Stultz <jstultz@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>, Wei Wang <wvw@...gle.com>,
        Midas Chien <midaschieh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Anton Vorontsov <anton@...msg.org>,
        "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        Tony Luck <tony.luck@...el.com>, kernel-team@...roid.com,
        Thomas Gleixner <tglx@...utronix.de>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [PATCH] pstore: Revert pmsg_lock back to a normal mutex

On Tue, Mar 7, 2023 at 9:09 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Fri, Mar 03, 2023 at 06:11:34PM +0000, Joel Fernandes wrote:
> > What  makes the rtmutex spin logic different from normal mutex in this
> > scenario, so that rtmutex wants to do that but normal ones dont?
>
> Regular mutex uses osq 'lock' to serialize waiters and only the top
> spinner gets to spin on the mutex itself, this greatly reduces the
> contention on the mutex.
>
> OSQ is FIFO, which is not what RT-mutex needs.

Got it, so basically OSQ ensures fairness as its FIFO and also reduces
lock contention because I am guessing the OSQ-spinners are spinning on
a per-spinner MCS node (that per-CPU optimistic_spin_node it appears).

This makes perfect sense now, thank you Peter!!!


 - Joel