From: Thomas Gleixner <tglx@linutronix.de>
To: Dmitry Vyukov <dvyukov@google.com>,
Jinjie Ruan <ruanjinjie@huawei.com>,
linux-man@vger.kernel.org
Cc: Mark Rutland <mark.rutland@arm.com>,
Mathias Stearn <mathias@mongodb.com>,
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>,
regressions@lists.linux.dev, linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Blake Oler <blake.oler@mongodb.com>
Subject: Re: [REGRESSION] rseq: refactoring in v6.19 broke everyone on arm64 and tcmalloc everywhere
Date: Thu, 23 Apr 2026 12:39:36 +0200 [thread overview]
Message-ID: <87ik9i0xlj.ffs@tglx> (raw)
In-Reply-To: <CACT4Y+bxnQyHGdVNE1BYTx+Z2-cscLb38HYS9jBM5gPAz8=4bw@mail.gmail.com>
On Thu, Apr 23 2026 at 07:53, Dmitry Vyukov wrote:
> On Thu, 23 Apr 2026 at 03:48, Jinjie Ruan <ruanjinjie@huawei.com> wrote:
>
> This part of the rseq man page needs to be fixed as well I think. The
> kernel no longer reliably provides clearing of rseq_cs on preemption,
> right?
>
> https://git.kernel.org/pub/scm/libs/librseq/librseq.git/tree/doc/man/rseq.2#n241
>
> "and set to NULL by the kernel when it restarts an assembly
> instruction sequence block,
> as well as when the kernel detects that it is preempting or delivering
> a signal outside of the range targeted by the rseq_cs."
The kernel clears rseq_cs reliably when user space was interrupted and:
the task was preempted
or
the return from interrupt delivers a signal
If the task invoked a syscall then there is absolutely no reason to do
either of this because syscalls from within a critical section are a
bug and catched when enabling rseq debugging.
The original code did this along with unconditionally updating CPU/MMCID
which resulted in ~15% performance regression on a syscall heavy
database benchmark once glibc started to register rseq.
Thanks,
tglx
next prev parent reply other threads:[~2026-04-23 10:39 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-22 9:50 [REGRESSION] rseq: refactoring in v6.19 broke everyone on arm64 and tcmalloc everywhere Mathias Stearn
2026-04-22 12:56 ` 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
2026-04-27 16:12 ` Linus Torvalds
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 [this message]
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
2026-04-27 18:35 ` Mathieu Desnoyers
2026-04-27 21:06 ` Thomas Gleixner
2026-04-28 6:11 ` Dmitry Vyukov
2026-04-28 8:07 ` Thomas Gleixner
2026-04-28 8:18 ` Thomas Gleixner
2026-04-28 10:53 ` Dmitry Vyukov
2026-04-28 13:31 ` Mathias Stearn
2026-04-28 15:46 ` Thomas Gleixner
2026-04-28 7:39 ` Peter Zijlstra
2026-04-28 8:13 ` Peter Zijlstra
2026-04-28 8:51 ` Thomas Gleixner
2026-04-28 8:03 ` Peter Zijlstra
2026-04-28 8:36 ` 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
2026-04-28 1:39 ` [PATCH] arm64/entry: Fix arm64-specific rseq brokenness Jinjie Ruan
2026-04-28 13:40 ` Mark Rutland
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