From: Florian Weimer <fweimer@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@kernel.org>,
Mathias Stearn <mathias@mongodb.com>,
Peter Zijlstra <peterz@infradead.org>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Boqun Feng <boqun.feng@gmail.com>,
"Paul E. McKenney" <paulmck@kernel.org>,
Chris Kennelly <ckennelly@google.com>,
Dmitry Vyukov <dvyukov@google.com>,
regressions@lists.linux.dev, linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
Ingo Molnar <mingo@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Jinjie Ruan <ruanjinjie@huawei.com>,
Blake Oler <blake.oler@mongodb.com>
Subject: Re: [REGRESSION] rseq: refactoring in v6.19 broke everyone on arm64 and tcmalloc everywhere
Date: Mon, 27 Apr 2026 09:06:13 +0200 [thread overview]
Message-ID: <lhuqzo051cq.fsf@oldenburg.str.redhat.com> (raw)
In-Reply-To: <CAHk-=wh=B3fqU9AaBsyViZR=eVTG5qa2CGyN=qxPROVxu9Gctg@mail.gmail.com> (Linus Torvalds's message of "Thu, 23 Apr 2026 14:28:35 -0700")
* Linus Torvalds:
>> // Note: this makes __rseq_abi.cpu_id_start unusable for its original purpose.
>>
>> Do you seriously want to proliferate that?
>
> Absolutely.
>
> That's how clever hacks work - they take advantage of things past
> their design parameters. "If it works, it's not stupid".
>
> We don't then turn around and say "you were clever, and we did
> something stupid, so now we'll hurt you".
>
> This is all 100% on the RSEQ kernel code, not on users who took
> advantage of it.
RSEQ was intended to be modular, with more than one library using it
within a process, without coordination (beyond sticking to the RSEQ
protocol). The tcmalloc approach is incompatible with that. Once
tcmalloc starts using RSEQ in its peculiar way, nothing else in the
process can, and vice versa. This is far from ideal because the
particular descheduling notification that tcmalloc uses could be
implemented in a much simpler way than full RSEQ, given its non-modular
nature.
Thanks,
Florian
next prev parent reply other threads:[~2026-04-27 7:06 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CAHnCjA25b+nO2n5CeifknSKHssJpPrjnf+dtr7UgzRw4Zgu=oA@mail.gmail.com>
2026-04-22 12:56 ` [REGRESSION] rseq: refactoring in v6.19 broke everyone on arm64 and tcmalloc everywhere Peter Zijlstra
2026-04-22 13:13 ` Peter Zijlstra
2026-04-23 10:38 ` Mathias Stearn
[not found] ` <CAHnCjA2fa+dP1+yCYNQrTXQaW-JdtfMj7wMikwMeeCRg-3NhiA@mail.gmail.com>
2026-04-23 11:48 ` Thomas Gleixner
2026-04-23 12:11 ` Mathias Stearn
2026-04-23 17:19 ` Thomas Gleixner
2026-04-23 17:38 ` Chris Kennelly
2026-04-23 17:47 ` Mathieu Desnoyers
2026-04-23 19:39 ` Thomas Gleixner
2026-04-23 17:41 ` Linus Torvalds
2026-04-23 18:35 ` Mathias Stearn
2026-04-23 18:53 ` Mark Rutland
2026-04-23 21:03 ` Thomas Gleixner
2026-04-23 21:28 ` Linus Torvalds
2026-04-23 23:08 ` Linus Torvalds
2026-04-27 7:06 ` Florian Weimer [this message]
2026-04-22 13:09 ` Mark Rutland
2026-04-22 17:49 ` Thomas Gleixner
2026-04-22 18:11 ` Mark Rutland
2026-04-22 19:47 ` Thomas Gleixner
2026-04-23 1:48 ` Jinjie Ruan
2026-04-23 5:53 ` Dmitry Vyukov
2026-04-23 10:39 ` Thomas Gleixner
2026-04-23 10:51 ` Mathias Stearn
2026-04-23 12:24 ` David Laight
2026-04-23 19:31 ` Thomas Gleixner
2026-04-24 7:56 ` Dmitry Vyukov
2026-04-24 8:32 ` Mathias Stearn
2026-04-24 9:30 ` Dmitry Vyukov
2026-04-24 14:16 ` Thomas Gleixner
2026-04-24 15:03 ` Peter Zijlstra
2026-04-24 19:44 ` Thomas Gleixner
2026-04-26 22:04 ` Thomas Gleixner
2026-04-27 7:40 ` Florian Weimer
2026-04-27 11:03 ` Thomas Gleixner
2026-04-23 12:11 ` Alejandro Colomar
2026-04-23 12:54 ` Mathieu Desnoyers
2026-04-23 12:29 ` Mathieu Desnoyers
2026-04-23 12:36 ` Dmitry Vyukov
2026-04-23 12:53 ` Mathieu Desnoyers
2026-04-23 12:58 ` Dmitry Vyukov
2026-04-24 16:45 ` [PATCH] arm64/entry: Fix arm64-specific rseq brokenness (was: Re: [REGRESSION] rseq: refactoring in v6.19 broke everyone on arm64) " Mark Rutland
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=lhuqzo051cq.fsf@oldenburg.str.redhat.com \
--to=fweimer@redhat.com \
--cc=blake.oler@mongodb.com \
--cc=boqun.feng@gmail.com \
--cc=catalin.marinas@arm.com \
--cc=ckennelly@google.com \
--cc=dvyukov@google.com \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mark.rutland@arm.com \
--cc=mathias@mongodb.com \
--cc=mathieu.desnoyers@efficios.com \
--cc=mingo@kernel.org \
--cc=paulmck@kernel.org \
--cc=peterz@infradead.org \
--cc=regressions@lists.linux.dev \
--cc=ruanjinjie@huawei.com \
--cc=tglx@kernel.org \
--cc=torvalds@linux-foundation.org \
--cc=will@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox