linux-kernel - Re: [RFC PATCH 71/86] treewide: lib: remove cond

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: <20231108144144.3d257286@gandalf.local.home>
Date:   Wed, 8 Nov 2023 14:41:44 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Ankur Arora <ankur.a.arora@...cle.com>,
        linux-kernel@...r.kernel.org, tglx@...utronix.de,
        peterz@...radead.org, torvalds@...ux-foundation.org,
        paulmck@...nel.org, linux-mm@...ck.org, x86@...nel.org,
        akpm@...ux-foundation.org, luto@...nel.org, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, mingo@...hat.com,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        willy@...radead.org, mgorman@...e.de, jon.grimm@....com,
        bharata@....com, raghavendra.kt@....com,
        boris.ostrovsky@...cle.com, konrad.wilk@...cle.com,
        jgross@...e.com, andrew.cooper3@...rix.com, mingo@...nel.org,
        bristot@...nel.org, mathieu.desnoyers@...icios.com,
        geert@...ux-m68k.org, glaubitz@...sik.fu-berlin.de,
        anton.ivanov@...bridgegreys.com, mattst88@...il.com,
        krypton@...ich-teichert.org, David.Laight@...lab.com,
        richard@....at, mjguzik@...il.com,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, Thomas Graf <tgraf@...g.ch>
Subject: Re: [RFC PATCH 71/86] treewide: lib: remove cond_resched()

On Wed, 8 Nov 2023 11:15:37 -0800
Kees Cook <keescook@...omium.org> wrote:

> FOr the memcpy_kunit.c cases, I don't think there are preemption
> locations in its loops. Perhaps I'm misunderstanding something? Why will
> the memcpy test no longer produce softlockup splats?

This patchset will switch over to a NEED_RESCHED_LAZY routine, so that
VOLUNTARY and NONE preemption models will be forced to preempt if its in
the kernel for too long.

Time slice is over: set NEED_RESCHED_LAZY

For VOLUNTARY and NONE, NEED_RESCHED_LAZY will not preempt the kernel (but
will preempt user space).

If in the kernel for over 1 tick (1ms for 1000Hz, 4ms for 250Hz, etc),
if NEED_RESCHED_LAZY is still set after one tick, then set NEED_RESCHED.

NEED_RESCHED will now schedule in the kernel once it is able to regardless
of preemption model. (PREEMPT_NONE will now use preempt_disable()).

This allows us to get rid of all cond_resched()s throughout the kernel as
this will be the new mechanism to keep from running inside the kernel for
too long. The watchdog is always longer than one tick.

-- Steve