From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Date: Sun, 17 Apr 2016 16:59:21 +0000 Subject: Re: [PATCH 10/11] x86, rwsem: provide __down_write_killable Message-Id: <20160417165920.GA9051@dhcp22.suse.cz> List-Id: References: <1460041951-22347-1-git-send-email-mhocko@kernel.org> <1460041951-22347-11-git-send-email-mhocko@kernel.org> <20160413090829.GB29579@gmail.com> <20160413091625.GF14351@dhcp22.suse.cz> <20160413091943.GA17858@gmail.com> <20160413102731.GA29896@gmail.com> <20160413124943.GH14351@dhcp22.suse.cz> In-Reply-To: <20160413124943.GH14351@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit To: Ingo Molnar Cc: LKML , Peter Zijlstra , Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , "David S. Miller" , Tony Luck , Andrew Morton , Chris Zankel , Max Filippov , x86@kernel.org, linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org, linux-s390@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, linux-xtensa@linux-xtensa.org, linux-arch@vger.kernel.org, Josh Poimboeuf On Wed 13-04-16 14:49:43, Michal Hocko wrote: > On Wed 13-04-16 12:27:31, Ingo Molnar wrote: > > > > * Ingo Molnar wrote: > > > > > I'm testing your patches today, if they are otherwise OK [...] > > > > got this build failure: > > > > ./arch/x86/include/asm/rwsem.h:106:2: error: ‘asm’ operand has impossible constraints > > Hmm, I have no idea why 64b didn't have problem with the asm but 32b > complains. Anyway, the following makes both happy. I have checked the > generated code for 64b and it hasn't changed after the patch. 32b also > seems to be generating a proper code. My gcc asm()-foo is rather weak so > I would feel better if somebody double checked after me. Peter, Ingo, does the patch makes sense to you? Thanks! > --- > From d23f4e6994670bf2c5d864f2190f21022b4499b2 Mon Sep 17 00:00:00 2001 > From: Michal Hocko > Date: Wed, 13 Apr 2016 14:21:25 +0200 > Subject: [PATCH] x86: __down_read_trylock fix 32b build failure > MIME-Version: 1.0 > Content-Type: text/plain; charset=UTF-8 > Content-Transfer-Encoding: 8bit > > Ingo has noticed the following compilation error with CONFIG_X86_32=y > ./arch/x86/include/asm/rwsem.h:106:2: error: ‘asm’ operand has impossible constraints > > The reason seems to be that 32b doesn't like ret being input and output > argument sharing the same register with sem which is only the input. Fix > this by making ret output only and use %3 (aka sem) for xadd. > > ret initialization is not needed now because this is done implicitly > by the asm even for the fast path as both sem and ret share the same > register. > > Reported-by: Ingo Molnar > Signed-off-by: Michal Hocko > --- > arch/x86/include/asm/rwsem.h | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/include/asm/rwsem.h b/arch/x86/include/asm/rwsem.h > index d759c5f70f49..453744c1d347 100644 > --- a/arch/x86/include/asm/rwsem.h > +++ b/arch/x86/include/asm/rwsem.h > @@ -102,9 +102,9 @@ static inline int __down_read_trylock(struct rw_semaphore *sem) > #define ____down_write(sem, slow_path) \ > ({ \ > long tmp; \ > - struct rw_semaphore* ret = sem; \ > + struct rw_semaphore* ret; \ > asm volatile("# beginning down_write\n\t" \ > - LOCK_PREFIX " xadd %1,(%2)\n\t" \ > + LOCK_PREFIX " xadd %1,(%3)\n\t" \ > /* adds 0xffff0001, returns the old value */ \ > " test " __ASM_SEL(%w1,%k1) "," __ASM_SEL(%w1,%k1) "\n\t" \ > /* was the active mask 0 before? */\ > @@ -112,7 +112,7 @@ static inline int __down_read_trylock(struct rw_semaphore *sem) > " call " slow_path "\n" \ > "1:\n" \ > "# ending down_write" \ > - : "+m" (sem->count), "=d" (tmp), "+a" (ret) \ > + : "+m" (sem->count), "=d" (tmp), "=a" (ret) \ > : "a" (sem), "1" (RWSEM_ACTIVE_WRITE_BIAS) \ > : "memory", "cc"); \ > ret; \ > -- > 2.8.0.rc3 > > -- > Michal Hocko > SUSE Labs -- Michal Hocko SUSE Labs