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Date:   Thu, 27 Jul 2023 19:52:59 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     syzbot <syzbot+8645fe63c4d22c8d27b8@syzkaller.appspotmail.com>
Cc:     akpm@linux-foundation.org, liam.howlett@oracle.com,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [mm?] WARNING: suspicious RCU usage in mas_walk (2)
Message-ID: <ZMK9C+iq3y8POOGp@casper.infradead.org>
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 <0000000000000aeb7f06015e5cbd@google.com>
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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

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..
 	 */