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[94.245.46.61]) by smtp.gmail.com with ESMTPSA id u3sm53372lfm.4.2021.09.22.03.41.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Sep 2021 03:41:43 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Wed, 22 Sep 2021 12:41:41 +0200 To: David Hildenbrand Cc: Uladzislau Rezki , LKML , Ping Fang , Andrew Morton , Roman Gushchin , Michal Hocko , Oscar Salvador , Linux Memory Management List Subject: Re: [PATCH v1] mm/vmalloc: fix exact allocations with an alignment > 1 Message-ID: <20210922104141.GA27011@pc638.lan> References: <20210908132727.16165-1-david@redhat.com> <20210916193403.GA1940@pc638.lan> <221e38c1-4b8a-8608-455a-6bde544adaf0@redhat.com> <20210921221337.GA60191@pc638.lan> <7f62d710-ca85-7d33-332a-25ff88b5452f@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7f62d710-ca85-7d33-332a-25ff88b5452f@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 22, 2021 at 10:34:55AM +0200, David Hildenbrand wrote: > > > No, that's leaking implementation details to the caller. And no, increasing > > > the range and eventually allocating something bigger (e.g., placing a huge > > > page where it might not have been possible) is not acceptable for KASAN. > > > > > > If you're terribly unhappy with this patch, > > Sorry to say but it simple does not make sense. > > > > Let's agree to disagree. > > find_vmap_lowest_match() is imprecise now and that's an issue for exact > allocations. We can either make it fully precise again (eventually degrading > allocation performance) or just special-case exact allocations to fix the > regression. > > I decided to go the easy path and do the latter; I do agree that making > find_vmap_lowest_match() fully precise again might be preferred -- we could > have other allocations failing right now although there are still suitable > holes. > > I briefly thought about performing the search in find_vmap_lowest_match() > twice. First, start the search without an extended range, and fallback to > the extended range if that search fails. Unfortunately, I think that still > won't make the function completely precise due to the way we might miss > searching some suitable subtrees. > > > > > > > please suggest something reasonable to fix exact allocations: > > > a) Fixes the KASAN use case. > > > b) Allows for automatic placement of huge pages for exact allocations. > > > c) Doesn't leak implementation details into the caller. > > > > > I am looking at it. > I am testing this: diff --git a/mm/vmalloc.c b/mm/vmalloc.c index dcf23d16a308..cdf3bda6313d 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -1161,18 +1161,14 @@ find_vmap_lowest_match(unsigned long size, { struct vmap_area *va; struct rb_node *node; - unsigned long length; /* Start from the root. */ node = free_vmap_area_root.rb_node; - /* Adjust the search size for alignment overhead. */ - length = size + align - 1; - while (node) { va = rb_entry(node, struct vmap_area, rb_node); - if (get_subtree_max_size(node->rb_left) >= length && + if (get_subtree_max_size(node->rb_left) >= size && vstart < va->va_start) { node = node->rb_left; } else { @@ -1182,9 +1178,9 @@ find_vmap_lowest_match(unsigned long size, /* * Does not make sense to go deeper towards the right * sub-tree if it does not have a free block that is - * equal or bigger to the requested search length. + * equal or bigger to the requested search size. */ - if (get_subtree_max_size(node->rb_right) >= length) { + if (get_subtree_max_size(node->rb_right) >= size) { node = node->rb_right; continue; } @@ -1192,16 +1188,30 @@ find_vmap_lowest_match(unsigned long size, /* * OK. We roll back and find the first right sub-tree, * that will satisfy the search criteria. It can happen - * only once due to "vstart" restriction. + * due to "vstart" restriction or an alignment overhead. */ while ((node = rb_parent(node))) { va = rb_entry(node, struct vmap_area, rb_node); if (is_within_this_va(va, size, align, vstart)) return va; - if (get_subtree_max_size(node->rb_right) >= length && + if (get_subtree_max_size(node->rb_right) >= size && vstart <= va->va_start) { + /* + * Shift the vstart forward, so we do not loop over same + * sub-tree force and back. The aim is to continue tree + * scanning toward higher addresses cutting off previous + * ones. + * + * Please note we update vstart with parent's start address + * adding "1" because we do not want to enter same sub-tree + * one more time after it has already been inspected and no + * suitable free block found there. + */ + vstart = va->va_start + 1; node = node->rb_right; + + /* Scan a sub-tree rooted at "node". */ break; } } so it handles any alignment and is accurate when it comes to searching the most lowest free block when user wants to allocate with a special alignment value. Could you please help and test the KASAN use case? Thanks! -- Vlad Rezki