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[156.34.48.30]) by smtp.gmail.com with ESMTPSA id v9sm2453624qkv.34.2020.11.20.10.23.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 20 Nov 2020 10:23:17 -0800 (PST) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1kgB40-008ub6-IN; Fri, 20 Nov 2020 14:23:16 -0400 Date: Fri, 20 Nov 2020 14:23:16 -0400 From: Jason Gunthorpe To: Daniel Vetter Cc: DRI Development , Intel Graphics Development , linux-mm@kvack.org, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, LKML , Dave Chinner , Qian Cai , Thomas =?utf-8?Q?Hellstr=C3=B6m?= , Andrew Morton , linux-rdma@vger.kernel.org, Maarten Lankhorst , Christian =?utf-8?B?S8O2bmln?= , "Matthew Wilcox (Oracle)" , Daniel Vetter Subject: Re: [PATCH 1/3] mm: Track mmu notifiers in fs_reclaim_acquire/release Message-ID: <20201120182316.GP244516@ziepe.ca> References: <20201120095445.1195585-1-daniel.vetter@ffwll.ch> <20201120095445.1195585-2-daniel.vetter@ffwll.ch> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20201120095445.1195585-2-daniel.vetter@ffwll.ch> Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Fri, Nov 20, 2020 at 10:54:42AM +0100, Daniel Vetter wrote: > fs_reclaim_acquire/release nicely catch recursion issues when > allocating GFP_KERNEL memory against shrinkers (which gpu drivers tend > to use to keep the excessive caches in check). For mmu notifier > recursions we do have lockdep annotations since 23b68395c7c7 > ("mm/mmu_notifiers: add a lockdep map for invalidate_range_start/end"). > > But these only fire if a path actually results in some pte > invalidation - for most small allocations that's very rarely the case. > The other trouble is that pte invalidation can happen any time when > __GFP_RECLAIM is set. Which means only really GFP_ATOMIC is a safe > choice, GFP_NOIO isn't good enough to avoid potential mmu notifier > recursion. > > I was pondering whether we should just do the general annotation, but > there's always the risk for false positives. Plus I'm assuming that > the core fs and io code is a lot better reviewed and tested than > random mmu notifier code in drivers. Hence why I decide to only > annotate for that specific case. > > Furthermore even if we'd create a lockdep map for direct reclaim, we'd > still need to explicit pull in the mmu notifier map - there's a lot > more places that do pte invalidation than just direct reclaim, these > two contexts arent the same. > > Note that the mmu notifiers needing their own independent lockdep map > is also the reason we can't hold them from fs_reclaim_acquire to > fs_reclaim_release - it would nest with the acquistion in the pte > invalidation code, causing a lockdep splat. And we can't remove the > annotations from pte invalidation and all the other places since > they're called from many other places than page reclaim. Hence we can > only do the equivalent of might_lock, but on the raw lockdep map. > > With this we can also remove the lockdep priming added in 66204f1d2d1b > ("mm/mmu_notifiers: prime lockdep") since the new annotations are > strictly more powerful. > > v2: Review from Thomas Hellstrom: > - unbotch the fs_reclaim context check, I accidentally inverted it, > but it didn't blow up because I inverted it immediately > - fix compiling for !CONFIG_MMU_NOTIFIER > > v3: Unbreak the PF_MEMALLOC_ context flags. Thanks to Qian for the > report and Dave for explaining what I failed to see. > > Cc: linux-fsdevel@vger.kernel.org > Cc: Dave Chinner > Cc: Qian Cai > Cc: linux-xfs@vger.kernel.org > Cc: Thomas Hellström (Intel) > Cc: Andrew Morton > Cc: Jason Gunthorpe > Cc: linux-mm@kvack.org > Cc: linux-rdma@vger.kernel.org > Cc: Maarten Lankhorst > Cc: Christian König > Cc: "Matthew Wilcox (Oracle)" > Signed-off-by: Daniel Vetter > --- > mm/mmu_notifier.c | 7 ------- > mm/page_alloc.c | 31 ++++++++++++++++++++----------- > 2 files changed, 20 insertions(+), 18 deletions(-) Reviewed-by: Jason Gunthorpe Jason