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Message-ID: <ZMK8ch6N/s3mbK6F@casper.infradead.org>
Date: Thu, 27 Jul 2023 19:50:26 +0100
From: Matthew Wilcox <willy@...radead.org>
To: syzbot <syzbot+8645fe63c4d22c8d27b8@...kaller.appspotmail.com>
Cc: akpm@...ux-foundation.org, liam.howlett@...cle.com,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [mm?] WARNING: suspicious RCU usage in mas_walk (2)
On Tue, Jul 25, 2023 at 11:57:22PM -0700, syzbot wrote:
> syzbot has bisected this issue to:
FWIW, this is unrelated to the previous issue. It's the caller of
mas_walk() that has violated the locking constraints, and mas_walk() is
simply reporting the issue. Is there a way to get syzbot to understand
that it needs to unwind the call-stack further to decide who to blame?
> commit a52f58b34afe095ebc5823684eb264404dad6f7b
> Author: Matthew Wilcox (Oracle) <willy@...radead.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
> final oops: https://syzkaller.appspot.com/x/report.txt?x=1443585ea80000
> console output: https://syzkaller.appspot.com/x/log.txt?x=1043585ea80000
> kernel config: https://syzkaller.appspot.com/x/.config?x=f481ab36ce878b84
> dashboard link: https://syzkaller.appspot.com/bug?extid=8645fe63c4d22c8d27b8
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1697cec9a80000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1566986ea80000
#syz test
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..
*/
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