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From: Hangbin Liu <liuhangbin@gmail.com>
To: David Laight <david.laight.linux@gmail.com>
Cc: Richard Henderson <richard.henderson@linaro.org>,
	Matt Turner <mattst88@gmail.com>,
	Magnus Lindholm <linmag7@gmail.com>,
	Vineet Gupta <vgupta@kernel.org>, Brian Cain <bcain@kernel.org>,
	"James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
	Helge Deller <deller@gmx.de>,
	Madhavan Srinivasan <maddy@linux.ibm.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Nicholas Piggin <npiggin@gmail.com>,
	"Christophe Leroy (CS GROUP)" <chleroy@kernel.org>,
	Paul Walmsley <pjw@kernel.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Alexandre Ghiti <alex@ghiti.fr>,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	Rich Felker <dalias@libc.org>,
	John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
	"David S. Miller" <davem@davemloft.net>,
	Andreas Larsson <andreas@gaisler.com>,
	Thomas Gleixner <tglx@kernel.org>, Ingo Molnar <mingo@redhat.com>,
	Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Chris Zankel <chris@zankel.net>,
	Max Filippov <jcmvbkbc@gmail.com>,
	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 <kuba@kernel.org>
Subject: Re: [PATCH] cmpxchg: allow const-qualified old value in cmpxchg()
Date: Thu, 2 Apr 2026 13:07:45 +0000	[thread overview]
Message-ID: <ac5qIUS5azbWAc9q@fedora> (raw)
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

WARNING: multiple messages have this Message-ID (diff)
From: Hangbin Liu <liuhangbin@gmail.com>
To: David Laight <david.laight.linux@gmail.com>
Cc: Richard Henderson <richard.henderson@linaro.org>,
	Matt Turner <mattst88@gmail.com>,
	Magnus Lindholm <linmag7@gmail.com>,
	Vineet Gupta <vgupta@kernel.org>, Brian Cain <bcain@kernel.org>,
	"James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
	Helge Deller <deller@gmx.de>,
	Madhavan Srinivasan <maddy@linux.ibm.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Nicholas Piggin <npiggin@gmail.com>,
	"Christophe Leroy (CS GROUP)" <chleroy@kernel.org>,
	Paul Walmsley <pjw@kernel.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Alexandre Ghiti <alex@ghiti.fr>,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	Rich Felker <dalias@libc.org>,
	John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
	"David S. Miller" <davem@davemloft.net>,
	Andreas Larsson <andreas@gaisler.com>,
	Thomas Gleixner <tglx@kernel.org>, Ingo Molnar <mingo@redhat.com>,
	Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Chris Zankel <chris@zankel.net>,
	Max Filippov <jcmvbkbc@gmail.com>,
	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 <kuba@kernel.org>
Subject: Re: [PATCH] cmpxchg: allow const-qualified old value in cmpxchg()
Date: Thu, 2 Apr 2026 13:07:45 +0000	[thread overview]
Message-ID: <ac5qIUS5azbWAc9q@fedora> (raw)
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

_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

WARNING: multiple messages have this Message-ID (diff)
From: Hangbin Liu <liuhangbin@gmail.com>
To: David Laight <david.laight.linux@gmail.com>
Cc: Richard Henderson <richard.henderson@linaro.org>,
	Matt Turner <mattst88@gmail.com>,
	Magnus Lindholm <linmag7@gmail.com>,
	Vineet Gupta <vgupta@kernel.org>, Brian Cain <bcain@kernel.org>,
	"James E.J. Bottomley" <James.Bottomley@hansenpartnership.com>,
	Helge Deller <deller@gmx.de>,
	Madhavan Srinivasan <maddy@linux.ibm.com>,
	Michael Ellerman <mpe@ellerman.id.au>,
	Nicholas Piggin <npiggin@gmail.com>,
	"Christophe Leroy (CS GROUP)" <chleroy@kernel.org>,
	Paul Walmsley <pjw@kernel.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Alexandre Ghiti <alex@ghiti.fr>,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	Rich Felker <dalias@libc.org>,
	John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
	"David S. Miller" <davem@davemloft.net>,
	Andreas Larsson <andreas@gaisler.com>,
	Thomas Gleixner <tglx@kernel.org>, Ingo Molnar <mingo@redhat.com>,
	Borislav Petkov <bp@alien8.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Chris Zankel <chris@zankel.net>,
	Max Filippov <jcmvbkbc@gmail.com>,
	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 <kuba@kernel.org>
Subject: Re: [PATCH] cmpxchg: allow const-qualified old value in cmpxchg()
Date: Thu, 2 Apr 2026 13:07:45 +0000	[thread overview]
Message-ID: <ac5qIUS5azbWAc9q@fedora> (raw)
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

_______________________________________________
linux-snps-arc mailing list
linux-snps-arc@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-snps-arc

  reply	other threads:[~2026-04-02 13:08 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-04-02  6:56 [PATCH] cmpxchg: allow const-qualified old value in cmpxchg() Hangbin Liu
2026-04-02  6:56 ` Hangbin Liu
2026-04-02  6:56 ` Hangbin Liu
2026-04-02  8:57 ` David Laight
2026-04-02  8:57   ` David Laight
2026-04-02  8:57   ` David Laight
2026-04-02 13:07   ` Hangbin Liu [this message]
2026-04-02 13:07     ` Hangbin Liu
2026-04-02 13:07     ` Hangbin Liu
2026-04-02 10:47 ` Peter Zijlstra
2026-04-02 10:47   ` Peter Zijlstra
2026-04-02 10:47   ` Peter Zijlstra

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