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From: Thomas Gleixner <tglx@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Mathias Stearn <mathias@mongodb.com>, Dmitry Vyukov
 <dvyukov@google.com>, Jinjie Ruan <ruanjinjie@huawei.com>,
 linux-man@vger.kernel.org, Mark Rutland <mark.rutland@arm.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, Ingo
 Molnar <mingo@kernel.org>, Blake Oler <blake.oler@mongodb.com>, Florian
 Weimer <fweimer@redhat.com>, Rich Felker <dalias@libc.org>, Matthew Wilcox
 <willy@infradead.org>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
 Linus Torvalds <torvalds@linuxfoundation.org>
Subject: Re: [REGRESSION] rseq: refactoring in v6.19 broke everyone on arm64
 and tcmalloc everywhere
In-Reply-To: <20260428073938.GH3126523@noisy.programming.kicks-ass.net>
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Date: Tue, 28 Apr 2026 10:51:29 +0200
Message-ID: <87zf2nxyb2.ffs@tglx>
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On Tue, Apr 28 2026 at 09:39, Peter Zijlstra wrote:
> On Mon, Apr 27, 2026 at 12:04:48AM +0200, Thomas Gleixner wrote:
>>  static inline void rseq_signal_deliver(struct ksignal *ksig, struct pt_regs *regs)
>>  {
>> -	if (IS_ENABLED(CONFIG_GENERIC_IRQ_ENTRY)) {
>> +	if (IS_ENABLED(CONFIG_GENERIC_IRQ_ENTRY) && rseq_optimized(current)) {
>
> rseq_optimized() already implies GENERIC_IRQ_ENTRY

Indeed.

>> +			u8			optimized;
>>  			union {
>>  				u16		error;
>>  				struct {
>
> I know you like the 'optimized' name, it is faster etc. However, the
> description there suggests: has_rseq_v2 not be a bad name.
>
> And while I write this, I figured we could have the value of has_rseq be
> 2, rather than 1, but this might end up generating worse code, dunno,
> haven't tried yet.

Tried that early on and it was worse, but back the approach has changed
since then and I just validated that it's actually fine to do so. Fixed.

Thanks,

        tglx