linux-kernel - Re: [PATCH v2] powerpc/32: Fix unpaired stwcx. on interrupt exit

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Message-ID: <aMQfD5M5yNmYxLho@gate>
Date: Fri, 12 Sep 2025 08:24:31 -0500
From: Segher Boessenkool <segher@...nel.crashing.org>
To: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>,
        Madhavan Srinivasan <maddy@...ux.ibm.com>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2] powerpc/32: Fix unpaired stwcx. on interrupt exit

Hi!

On Fri, Sep 12, 2025 at 10:37:34AM +0200, Christophe Leroy wrote:
>  BEGIN_FTR_SECTION
> +	lwarx   r0,0,r1
> +END_FTR_SECTION_IFSET(CPU_FTR_NEED_PAIRED_STWCX)
>  	stwcx.	r0,0,r1		/* to clear the reservation */
> -FTR_SECTION_ELSE
> -	lwarx	r0,0,r1
> -ALT_FTR_SECTION_END_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)

Hrm.  So this is for V'ger (mpc7450)?  What kind of issues does that
old thing have with unpaired larx/stcx., some performance impact?

The extra "dummy" larx has serious performance impact itself, on most
implementations (also on all newer stuff).


Segher