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Date: Tue, 26 May 2020 21:22:45 -0400 From: Qian Cai <cai@....pw> To: Paul Mackerras <paulus@...abs.org> Cc: mpe@...erman.id.au, benh@...nel.crashing.org, aik@...abs.ru, paulmck@...nel.org, linuxppc-dev@...ts.ozlabs.org, kvm-ppc@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH] powerpc/kvm/book3s64/vio: fix some RCU-list locks On Wed, May 27, 2020 at 11:13:23AM +1000, Paul Mackerras wrote: > On Sun, May 10, 2020 at 01:18:34AM -0400, Qian Cai wrote: > > It is unsafe to traverse kvm->arch.spapr_tce_tables and > > stt->iommu_tables without the RCU read lock held. Also, add > > cond_resched_rcu() in places with the RCU read lock held that could take > > a while to finish. > > This mostly looks fine. The cond_resched_rcu() in kvmppc_tce_validate > doesn't seem necessary (the list would rarely have more than a few > dozen entries) and could be a performance problem given that TCE > validation is a hot-path. > > Are you OK with me modifying the patch to take out that > cond_resched_rcu(), or is there some reason why it's essential that it > be there? Feel free to take out that cond_resched_rcu(). Your reasoning makes sense.
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