linux-kernel - Re: [PATCH v2 7/9] sched: define TIF_ALLOW

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: <878r8wgg3b.ffs@tglx>
Date:   Sun, 24 Sep 2023 09:55:52 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ankur Arora <ankur.a.arora@...cle.com>,
        linux-kernel@...r.kernel.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, mgorman@...e.de,
        rostedt@...dmis.org, jon.grimm@....com, bharata@....com,
        raghavendra.kt@....com, boris.ostrovsky@...cle.com,
        konrad.wilk@...cle.com, jgross@...e.com, andrew.cooper3@...rix.com
Subject: Re: [PATCH v2 7/9] sched: define TIF_ALLOW_RESCHED

On Sun, Sep 24 2023 at 08:19, Matthew Wilcox wrote:
> On Sun, Sep 24, 2023 at 12:50:43AM +0200, Thomas Gleixner wrote:
>> cond_resched() cannot nest and is obviously scope-less.
>> 
>> The TIF_ALLOW_RESCHED mechanism, which sparked this discussion only
>> pretends to be scoped.
>> 
>> As Peter pointed out it does not properly nest with other mechanisms and
>> it cannot even nest in itself because it is boolean.
>
> We can nest a single bit without turning it into a counter -- we
> do this for memalloc_nofs_save() for example.  Simply return the
> current value of the bit, and pass it to _restore().

Right.

That works, but the reverse logic still does not make sense:

        allow_resched();
        ....
        spin_lock();

while
        resched_now_is_suboptimal();
        ...
        spin_lock();

works.

Thanks,

        tglx