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: <871qk5782i.fsf@kurt>
Date:   Thu, 27 Apr 2023 15:45:09 +0200
From:   Kurt Kanzenbach <kurt@...utronix.de>
To:     Jan Kiszka <jan.kiszka@...mens.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Bouska, Zdenek" <zdenek.bouska@...mens.com>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>
Cc:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-rt-users@...r.kernel.org" <linux-rt-users@...r.kernel.org>,
        Nishanth Menon <nm@...com>, Puranjay Mohan <p-mohan@...com>
Subject: Re: Unfair qspinlocks on ARM64 without LSE atomics => 3ms delay in
 interrupt handling

On Thu Apr 27 2023, Jan Kiszka wrote:
> On 26.04.23 23:29, Thomas Gleixner wrote:
>> On Wed, Apr 26 2023 at 12:03, Zdenek Bouska wrote:
>>> following patch is my current approach for fixing this issue. I introduced
>>> big_cpu_relax(), which uses Will's implementation [1] on ARM64 without
>>> LSE atomics and original cpu_relax() on any other CPU.
>> 
>> Why is this interrupt handling specific? Just because it's the place
>> where you observed it?
>> 
>> That's a general issue for any code which uses atomics for forward
>> progress. LL/SC simply does not guarantee that.
>> 
>> So if that helps, then this needs to be addressed globaly and not with
>> some crude hack in the interrupt handling code.
>
> My impression is that the retry loop of irq_finalize_oneshot is
> particularly susceptible to that issue due to the high acquire/relax
> pressure and inter-dependency between holder and waiter it generates -
> which does not mean it cannot occur in other places.
>
> Are we aware of other concrete case where it bites? Even with just
> "normal" contented spin_lock usage?

Well, some years ago I've observed a similar problem with ARM64
spinlocks, cpu_relax() and retry loops (in the futex code). It also
generated latency spikes up to 2-3ms. Back then, it was easily
reproducible using stress-ng --ptrace 4.

Thanks,
Kurt

Download attachment "signature.asc" of type "application/pgp-signature" (862 bytes)

Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ