linux-kernel - Re: [PATCH hotfix 6.12 v3 4/5] mm: refactor arch_validate

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Message-ID: <32e59a00-a174-4fcc-befd-56915cfb01d1@lucifer.local>
Date: Tue, 29 Oct 2024 15:52:14 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Yang Shi <shy828301@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Xu <peterx@...hat.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Mark Brown <broonie@...nel.org>,
        "David S . Miller" <davem@...emloft.net>,
        Andreas Larsson <andreas@...sler.com>
Subject: Re: [PATCH hotfix 6.12 v3 4/5] mm: refactor arch_validate_flags()
 and arm64 MTE handling

On Tue, Oct 29, 2024 at 08:43:04AM -0700, Yang Shi wrote:

>
> Sorry for chiming in late. This looks problematic IIUC. The patch 5/5
> moved arch_validate_flags() before call_mmap() as the commit log said.
> But shmem_file() does this check:
> mapping->a_ops == &shmem_aops
>
> But mapping->a_ops is not initialized until shmem_mmap(), which is
> called by call_mmap().
>
> So shmem_file() should always return false here. Did I miss something?

Well firstly this is tested and works so you did miss something :)

Bu shmem_mmap() is not setting mapping->a_ops, it's setting vma->vm_ops.

__shmem_get_inode() and shmem_symlink() set mapping->a_ops.