linux-kernel - Re: linux-next: manual merge of the mm tree with Linus' tree

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Message-ID: <20230728092915.732d4115@canb.auug.org.au>
Date:   Fri, 28 Jul 2023 09:29:15 +1000
From:   Stephen Rothwell <sfr@...b.auug.org.au>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Jann Horn <jannh@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Suren Baghdasaryan <surenb@...gle.com>
Subject: Re: linux-next: manual merge of the mm tree with Linus' tree

Hi all,

On Fri, 28 Jul 2023 09:18:49 +1000 Stephen Rothwell <sfr@...b.auug.org.au> wrote:
>
> Today's linux-next merge of the mm tree got a conflict in:
> 
>   mm/memory.c
> 
> between commit:
> 
>   657b5146955e ("mm: lock_vma_under_rcu() must check vma->anon_vma under vma lock")
> 
> from Linus' tree and commits:
> 
>   69f6bbd1317f ("mm: handle userfaults under VMA lock")
>   a3bdf38e85aa ("mm: allow per-VMA locks on file-backed VMAs")
> 
> from the mm tree.
> 
> I fixed it up (I think, please check - see below) and can carry the fix
> as necessary. This is now fixed as far as linux-next is concerned, but
> any non trivial conflicts should be mentioned to your upstream
> maintainer when your tree is submitted for merging.  You may also want
> to consider cooperating with the maintainer of the conflicting tree to
> minimise any particularly complex conflicts.
> 
> -- 
> Cheers,
> Stephen Rothwell
> 
> diff --cc mm/memory.c
> index ca632b58f792,271982fab2b8..000000000000
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@@ -5392,32 -5597,18 +5597,21 @@@ retry
>   	if (!vma)
>   		goto inval;
>   
> - 	/* Only anonymous and tcp vmas are supported for now */
> - 	if (!vma_is_anonymous(vma) && !vma_is_tcp(vma))
>  -	/* find_mergeable_anon_vma uses adjacent vmas which are not locked */
>  -	if (vma_is_anonymous(vma) && !vma->anon_vma)
> --		goto inval;
> --
>   	if (!vma_start_read(vma))
>   		goto inval;
>   
>  +	/*
>  +	 * find_mergeable_anon_vma uses adjacent vmas which are not locked.
>  +	 * This check must happen after vma_start_read(); otherwise, a
>  +	 * concurrent mremap() with MREMAP_DONTUNMAP could dissociate the VMA
>  +	 * from its anon_vma.
>  +	 */
> - 	if (unlikely(!vma->anon_vma && !vma_is_tcp(vma)))
> - 		goto inval_end_read;
> - 
> - 	/*
> - 	 * Due to the possibility of userfault handler dropping mmap_lock, avoid
> - 	 * it for now and fall back to page fault handling under mmap_lock.
> - 	 */
> - 	if (userfaultfd_armed(vma))
> ++	if (unlikely(vma_is_anonymous(vma) && !vma_is_tcp(vma)))
>  +		goto inval_end_read;
>  +
>   	/* Check since vm_start/vm_end might change before we lock the VMA */
>  -	if (unlikely(address < vma->vm_start || address >= vma->vm_end)) {
>  -		vma_end_read(vma);
>  -		goto inval;
>  -	}
>  +	if (unlikely(address < vma->vm_start || address >= vma->vm_end))
>  +		goto inval_end_read;
>   
>   	/* Check if the VMA got isolated after we found it */
>   	if (vma->detached) {

Sorry, doesn't even build ... let me try that again.

-- 
Cheers,
Stephen Rothwell

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