From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Date: Wed, 22 Aug 2018 07:02:41 +0000 Subject: Re: [PATCH 10/20] powerpc/dma-noncoherent: don't disable irqs over kmap_atomic Message-Id: <20180822070241.GD19284@lst.de> List-Id: References: <20180730163824.10064-1-hch@lst.de> <20180730163824.10064-11-hch@lst.de> In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Benjamin Herrenschmidt Cc: Christoph Hellwig , Paul Mackerras , Michael Ellerman , Tony Luck , Fenghua Yu , Konrad Rzeszutek Wilk , Robin Murphy , linuxppc-dev@lists.ozlabs.org, iommu@lists.linux-foundation.org, linux-ia64@vger.kernel.org On Thu, Aug 09, 2018 at 10:27:46AM +1000, Benjamin Herrenschmidt wrote: > On Mon, 2018-07-30 at 18:38 +0200, Christoph Hellwig wrote: > > The requirement to disable local irqs over kmap_atomic is long gone, > > so remove those calls. > > Really ? I'm trying to verify that and getting lost in a mess of macros > from hell in the per-cpu stuff but if you look at our implementation > of kmap_atomic_prot(), all it does is a preempt_disable(), and then > it uses kmap_atomic_idx_push(): > > int idx = __this_cpu_inc_return(__kmap_atomic_idx) - 1; > > Note the use of __this_cpu_inc_return(), not this_cpu_inc_return(), > ie this is the non-interrupt safe version... Looks like the powerpc variant indeed isn't save. I did look a bit more through the code and history, and it seems like we remove the need to disable irqs when called from process context a while ago, but we still require disabling irqs when called from irq context. Given that this code can also be called from irq context we'll have to keep the local_irq_save.