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b=vWd9PH4+zF/ek7rkQK7nPfLAYMQVfP5lqY+NM+kCTLWqo+X38fwCxKAyy0FnFyG1P MiUegVKczEMU5b8yTm6ic0qG+vKHG1auoyMcR+HkEBJOqDBamYBDAP6k7kPNednXR2 obkSLcLVKAuZAsYFODXUXZM6LIA732tk25e5j3Lg= Date: Sun, 5 Jul 2026 15:27:08 -0700 From: Andrew Morton To: Hajime Tazaki Cc: liam@infradead.org, ljs@kernel.org, vbabka@kernel.org, jannh@google.com, pfalcato@suse.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: nommu: point to the write iterator upon split_vma Message-Id: <20260705152708.582fd8d87561f600da23c0a7@linux-foundation.org> In-Reply-To: <20260702012546.665383-1-thehajime@gmail.com> References: <20260702012546.665383-1-thehajime@gmail.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: A2FC440005 X-Stat-Signature: tj6apg7hudu4c5yqdtqp6x4aodyfio1r X-HE-Tag: 1783290430-30260 X-HE-Meta: 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 5/iQz55v s8/+77x4D+0KQiF40JppgKRzoarD+pgIl5pQu2AUez1f/Nc3VRo/1aATIJqL8wARbiaSbYRH/Kxj2qgo2pGU5q2/ZWMjJK3xIrbTZMjS8kQ5ryE6mS/PviCVtU9nyQapbfc/sIYuGmdyBa027pTg+TGJrhRTz/S2e/+sn2sj5acEmrfHRYan40vXQ17u4cZfY9DujMaZEwWp0Cc9askn8npU3hnve/Ak9NS5jFaWnq/Nj9ffTF6sPnOUTcz0DKRw7bHtg+oBJ1Nu9fIruRaxLFwCZqul9Lxc5L0kewcOkOMcCvgMJuGl75RezEKshBD0wsSB3LlPDh7hw8il7c1jLiJ1N0iDtRlHqHABBezCPMgUx7HmIPaskRGkhGj8LPPa/spfP Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 2 Jul 2026 10:25:46 +0900 Hajime Tazaki wrote: > When users munmap(2) the partial region allocated by mmap, it might > split the original region if necessary and shrink to the right size. > At the begining of vmi_shrink_vma(), it clears the unused part but > generates assetion when the shrink happenes after split_vma(). > > This commit fixes this issue by configuring the right pointer to the > iterator at the end of split_vma(). > > This was detected with a LTP (Linux Test Project) test, which linked > below, on the nommu UML environment (out-of-tree extension to UML). > > Here is a minimal reproducible chunk of code for this issue: > > void *addr; > size_t pagesize = getpagesize(); > > addr = mmap(NULL, pagesize * 4, PROT_READ | PROT_WRITE, > MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); > munmap(addr + pagesize * 1, pagesize); > > This is the console output with CONFIG_DEBUG_MAPLE_TREE=y. > > nommu: WARN at __mas_set_range:791 (1) > MAS: tree=0000000091c23b08 enode=0000000065057663 > (ma_active) > Store Type: > node_store > [9/9] index=70af8000 last=ffffffffffffffff > min=0 max=ffffffffffffffff sheaf=0000000000000000, request 0 > depth=0, flags=0 > maple_tree(0000000091c23b08) flags 307, height 1 root 0000000083394c06 > 0-ffffffffffffffff: node 0000000010c90bd6 depth 0 type 1 parent > 0000000050e1ddf8 contents: 0000000000000000 707A > 7FFF 00000000eb0ac2b5 707AFFFF 0000000000000000 7093FFFF > 0000000045ead616 7095FFFF 0000000000000000 7096CFFF 000 > 00000681c7151 7096FFFF 0000000000000000 70AF3FFF 000000006c78b9e9 > 70AF4FFF 000000001914ab0b 70AF7FFF 00000000000 > 00000 FFFFFFFFFFFFFFFF 0000000000000000 0 0000000000000000 0 > 0000000000000000 0 0000000000000000 0 0000000000000 > 000 0 00000000bca8be4f > 0-707a7fff: 0000000000000000 > 707a8000-707affff: 00000000eb0ac2b5 > 707b0000-7093ffff: 0000000000000000 > 70940000-7095ffff: 0000000045ead616 > 70960000-7096cfff: 0000000000000000 > 7096d000-7096ffff: 00000000681c7151 > 70970000-70af3fff: 0000000000000000 > 70af4000-70af4fff: 000000006c78b9e9 > 70af5000-70af7fff: 000000001914ab0b > 70af8000-ffffffffffffffff: 0000000000000000 > nommu: Pass: 796 Run:797 Thanks. Unfortunately we aren't very diligent about the nommu code (are we?). Perhaps appropriately - clearly this code doesn't get used a lot. It appears that AI review has found another issue in there: https://sashiko.dev/#/patchset/20260702012546.665383-1-thehajime@gmail.com > --- a/mm/nommu.c > +++ b/mm/nommu.c > @@ -1367,6 +1367,10 @@ static int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma, > setup_vma_to_mm(vma, mm); > setup_vma_to_mm(new, mm); > vma_iter_store_new(vmi, new); > + > + /* vmi should point lower address */ > + if (new_below) > + vma_next(vmi); > mm->map_count++; > return 0; Lorenzo, others: do you have the time? Thanks.