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Date:   Thu, 27 Jul 2023 11:53:02 -0700
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Message-ID: <0000000000004ccc7906017c79e0@google.com>
Subject: Re: [syzbot] [mm?] WARNING: suspicious RCU usage in mas_walk (2)
From:   syzbot <syzbot+8645fe63c4d22c8d27b8@syzkaller.appspotmail.com>
To:     willy@infradead.org
Cc:     akpm@linux-foundation.org, liam.howlett@oracle.com,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        syzkaller-bugs@googlegroups.com, willy@infradead.org
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> On Tue, Jul 25, 2023 at 11:57:22PM -0700, syzbot wrote:
>> syzbot has bisected this issue to:
>> 
>> commit a52f58b34afe095ebc5823684eb264404dad6f7b
>> Author: Matthew Wilcox (Oracle) <willy@infradead.org>
>> Date:   Mon Jul 24 18:54:10 2023 +0000
>> 
>>     mm: handle faults that merely update the accessed bit under the VMA lock
>> 
>> bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=1783585ea80000
>> start commit:   [unknown] 
>> git tree:       linux-next
>
> #syz test linux-next a52f58b34afe095ebc5823684eb264404dad6f7b

"linux-next" does not look like a valid git repo address.

>
> diff --git a/mm/memory.c b/mm/memory.c
> index 20a2e9ed4aeb..57b271108bdc 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3567,6 +3567,12 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf)
>  		return 0;
>  	}
>  copy:
> +	if ((vmf->flags & FAULT_FLAG_VMA_LOCK) && !vma->anon_vma) {
> +		pte_unmap_unlock(vmf->pte, vmf->ptl);
> +		vma_end_read(vmf->vma);
> +		return VM_FAULT_RETRY;
> +	}
> +
>  	/*
>  	 * Ok, we need to copy. Oh, well..
>  	 */