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[142.68.128.5]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-6d8da6b2291sm48868886d6.58.2024.12.09.06.20.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 09 Dec 2024 06:20:14 -0800 (PST) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1tKecP-00000009sI1-2JGA; Mon, 09 Dec 2024 10:20:13 -0400 Date: Mon, 9 Dec 2024 10:20:13 -0400 From: Jason Gunthorpe To: "Luis Claudio R. Goncalves" Cc: Thierry Reding , Krishna Reddy , Will Deacon , Robin Murphy , Joerg Roedel , Jonathan Hunter , linux-kernel@vger.kernel.org, iommu@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-tegra@vger.kernel.org, Sebastian Andrzej Siewior , Steven Rostedt , linux-rt-devel@lists.linux.dev Subject: Re: [PATCH v2] iommu/tegra241-cmdqv: do not use smp_processor_id in preemptible context Message-ID: <20241209142013.GC1888283@ziepe.ca> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20241209_062016_224965_CA0D4C32 X-CRM114-Status: GOOD ( 15.74 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Dec 06, 2024 at 10:01:14AM -0300, Luis Claudio R. Goncalves wrote: > During boot some of the calls to tegra241_cmdqv_get_cmdq() will happen > in preemptible context. As this function calls smp_processor_id(), if > CONFIG_DEBUG_PREEMPT is enabled, these calls will trigger a series of > "BUG: using smp_processor_id() in preemptible" backtraces. > > As tegra241_cmdqv_get_cmdq() only calls smp_processor_id() to use the > CPU number as a factor to balance out traffic on cmdq usage, it is safe > to use raw_smp_processor_id() here. > > v2: Sebastian helped identify that the problem was not exclusive to kernels > with PREEMPT_RT enabled. The delta between v1 and v2 is the description. > > Signed-off-by: Luis Claudio R. Goncalves > --- > drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) Makes sense Reviewed-by: Jason Gunthorpe Jason