linux-kernel - Re: kernel BUG at mm/shmem.c:LINE!

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Date:   Thu, 26 Jul 2018 09:40:20 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     Matthew Wilcox <willy@...radead.org>
cc:     Hugh Dickins <hughd@...gle.com>,
        syzbot <syzbot+b8e0dfee3fd8c9012771@...kaller.appspotmail.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: kernel BUG at mm/shmem.c:LINE!

On Thu, 26 Jul 2018, Matthew Wilcox wrote:
> On Wed, Jul 25, 2018 at 11:53:15PM -0700, Hugh Dickins wrote:
> 
> and fixing the bug differently ;-)  But many thanks for spotting it!

I thought you might :)

> 
> I'll look into the next bug you reported ...

No need: that idea now works a lot better when I use the initialized
"start", instead of the uninitialized "index".

Hugh

--- mmotm/mm/khugepaged.c	2018-07-20 17:54:41.978805312 -0700
+++ linux/mm/khugepaged.c	2018-07-26 09:20:22.416949014 -0700
@@ -1352,6 +1352,7 @@ static void collapse_shmem(struct mm_str
 			goto out;
 	} while (1);
 
+	xas_set(&xas, start);
 	for (index = start; index < end; index++) {
 		struct page *page = xas_next(&xas);