linux-kernel - Re: [PATCH RESEND 1/2] x86/locking: Use ALT_OUTPUT_SP() for percpu_{,try_}cmpxchg{64,128}

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Message-ID: <04adffd9-2900-4cdb-a557-1c486a87b522@intel.com>
Date: Thu, 13 Feb 2025 12:43:13 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Uros Bizjak <ubizjak@...il.com>, x86@...nel.org, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...nel.org>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 "H. Peter Anvin" <hpa@...or.com>, Dennis Zhou <dennis@...nel.org>,
 Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>,
 "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [PATCH RESEND 1/2] x86/locking: Use ALT_OUTPUT_SP() for
 percpu_{,try_}cmpxchg{64,128}_op()

On 2/13/25 11:14, Uros Bizjak wrote:
> percpu_{,try_}cmpxchg{64,128}() macros use CALL instruction inside
> asm statement in one of their alternatives. Use ALT_OUTPUT_SP()
> macro to add required dependence on %esp register.

Is this just a pedantic fix? Or is there an actual impact to end users
that needs to be considered?

Basically, you've told me what the patch does, but not why anyone should
care or why it should be applied.