linux-kernel - Re: [PATCH v4 00/15] Add futex2 syscalls

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Date:   Tue, 08 Jun 2021 20:19:21 +0200
From:   Florian Weimer <fweimer@...hat.com>
To:     Adhemerval Zanella <adhemerval.zanella@...aro.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        linux-kselftest@...r.kernel.org, joel@...lfernandes.org,
        Andrey Semashev <andrey.semashev@...il.com>,
        kernel@...labora.com, shuah@...nel.org,
        Davidlohr Bueso <dave@...olabs.net>,
        Peter Oskolkov <posk@...k.io>, corbet@....net,
        krisman@...labora.com, malteskarupke@...tmail.fm,
        Ingo Molnar <mingo@...hat.com>,
        Darren Hart <dvhart@...radead.org>, acme@...nel.org,
        Steven Rostedt <rostedt@...dmis.org>,
        André Almeida <andrealmeid@...labora.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        libc-alpha@...rceware.org, linux-api@...r.kernel.org,
        z.figura12@...il.com, Nicholas Piggin <npiggin@...il.com>,
        linux-kernel@...r.kernel.org, pgriffais@...vesoftware.com
Subject: Re: [PATCH v4 00/15] Add futex2 syscalls

* Adhemerval Zanella:

> Also currently we don't have a specific usage.  The proposed patch to
> add the 'pthread_mutex_lock_any' and 'pthreada_timedlock_any' [3] 
> also did not gave much detail in realword usages or how it can be
> leveraged.

The current rwlock implementation in glibc uses a torn 32-bit futex read
which is part of an atomically updated 64-bit word.  That's just really,
really ugly, and I suspect we could make that go away with futex2.

Thanks,
Florian