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Bottomley" , Helge Deller , Madhavan Srinivasan , Michael Ellerman , Nicholas Piggin , "Christophe Leroy (CS GROUP)" , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , Yoshinori Sato , Rich Felker , John Paul Adrian Glaubitz , "David S. Miller" , Andreas Larsson , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Chris Zankel , Max Filippov , linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org, linux-snps-arc@lists.infradead.org, linux-hexagon@vger.kernel.org, linux-parisc@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, Jakub Kicinski Subject: Re: [PATCH] cmpxchg: allow const-qualified old value in cmpxchg() Message-ID: References: <20260402-cmpxchg-v1-1-4561e2c05d2c@gmail.com> <20260402095747.6efbd456@pumpkin> Precedence: bulk X-Mailing-List: sparclinux@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260402095747.6efbd456@pumpkin> On Thu, Apr 02, 2026 at 09:57:47AM +0100, David Laight wrote: > > diff --git a/arch/alpha/include/asm/cmpxchg.h b/arch/alpha/include/asm/cmpxchg.h > > index ae1b96479d0c..b4b8dac759c4 100644 > > --- a/arch/alpha/include/asm/cmpxchg.h > > +++ b/arch/alpha/include/asm/cmpxchg.h > > @@ -234,7 +234,7 @@ ____cmpxchg(volatile void *ptr, unsigned long old, unsigned long new, > > > > #define arch_cmpxchg_local(ptr, o, n) \ > > ({ \ > > - __typeof__(*(ptr)) _o_ = (o); \ > > + __typeof__(*(ptr)) _o_ = (__typeof__(*(ptr)))(o); \ > > __typeof__(*(ptr)) _n_ = (n); \ > > (__typeof__(*(ptr))) ____cmpxchg((ptr), (unsigned long)_o_, \ > > (unsigned long)_n_, \ > > That looks like it loses the check that 'o' has the same type as '*ptr'. > Maybe this works? > auto _o_ = 1 ? (o) : *(ptr); > Oh, I didn't notice this. Thanks for the comment! Best Regards Hangbin