From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org (ozlabs.org [103.22.144.67]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 7D0C41A0076 for ; Wed, 20 May 2015 11:00:08 +1000 (AEST) Message-ID: <1432083608.20823.19.camel@neuling.org> Subject: Re: [PATCH] powerpc: Make doorbell check preemption safe From: Michael Neuling To: "Shreyas B. Prabhu" Date: Wed, 20 May 2015 11:00:08 +1000 In-Reply-To: <1432062014-9115-1-git-send-email-shreyas@linux.vnet.ibm.com> References: <1432062014-9115-1-git-send-email-shreyas@linux.vnet.ibm.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Cc: paulus@samba.org, linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, 2015-05-20 at 00:30 +0530, Shreyas B. Prabhu wrote: > Doorbell can be used to cause ipi on cpus which are sibling threads on > the same core. So icp_native_cause_ipi checks if the destination cpu > is a sibling thread of the current cpu and uses doorbell in such cases. >=20 > But while running with CONFIG_PREEMPT=3Dy, since this section is > preemtible, we can run into issues if after we check if the destination > cpu is a sibling cpu, the task gets migrated from a sibling cpu to a > cpu on another core. >=20 > Fix this by using get_cpu()/ put_cpu() Thanks. Looks good and it's boots for me. Signed-off-by: Michael Neuling > Signed-off-by: Shreyas B. Prabhu > --- > arch/powerpc/sysdev/xics/icp-native.c | 14 +++++++++----- > 1 file changed, 9 insertions(+), 5 deletions(-) >=20 > diff --git a/arch/powerpc/sysdev/xics/icp-native.c b/arch/powerpc/sysdev/= xics/icp-native.c > index 2fc4cf1..62fd478 100644 > --- a/arch/powerpc/sysdev/xics/icp-native.c > +++ b/arch/powerpc/sysdev/xics/icp-native.c > @@ -147,12 +147,16 @@ static void icp_native_cause_ipi(int cpu, unsigned = long data) > { > kvmppc_set_host_ipi(cpu, 1); > #ifdef CONFIG_PPC_DOORBELL > - if (cpu_has_feature(CPU_FTR_DBELL) && > - (cpumask_test_cpu(cpu, cpu_sibling_mask(smp_processor_id())))) > - doorbell_cause_ipi(cpu, data); > - else > + if (cpu_has_feature(CPU_FTR_DBELL)) { > + if (cpumask_test_cpu(cpu, cpu_sibling_mask(get_cpu()))) { > + doorbell_cause_ipi(cpu, data); > + put_cpu(); > + return; > + } > + put_cpu(); > + } > #endif > - icp_native_set_qirr(cpu, IPI_PRIORITY); > + icp_native_set_qirr(cpu, IPI_PRIORITY); > } > =20 > /*