From: John Hubbard <jhubbard@nvidia.com>
To: Minchan Kim <minchan@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Mike Kravetz <mike.kravetz@oracle.com>,
syzbot <syzbot+acf65ca584991f3cc447@syzkaller.appspotmail.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
llvm@lists.linux.dev, nathan@kernel.org, ndesaulniers@google.com,
syzkaller-bugs@googlegroups.com, trix@redhat.com,
Matthew Wilcox <willy@infradead.org>,
Stephen Rothwell <sfr@canb.auug.org.au>,
David Hildenbrand <david@redhat.com>
Subject: Re: [syzbot] WARNING in follow_hugetlb_page
Date: Fri, 13 May 2022 18:16:46 -0700 [thread overview]
Message-ID: <1c6405b0-271e-22b8-961e-629a2a8bbcf0@nvidia.com> (raw)
In-Reply-To: <d97d8a00-e9e0-278f-0c3f-71162afa48b1@nvidia.com>
On 5/13/22 17:56, John Hubbard wrote:
> On 5/13/22 17:26, Minchan Kim wrote:
>> Anything else further can we get insight from the warning?
>>
>> For example, pin_user_pages going on against a hugetlb page
>> which are concurrently running alloc_contig_range(it's
>> exported function so anyone can call randomly) so
>> alloc_contig_range changes pageblock type as MIGRATE_ISOLATE
>> under us so the hit at the warning?
>
> Well, yes. First of all, the comments above the warning that fired have
> gone a little bit stale: they claim that we can only hit the warning if
> the page refcount overflows. However, we almost certainly got here via:
>
> try_grab_folio()
> /*
> * Can't do FOLL_LONGTERM + FOLL_PIN gup fast path if not in a
> * right zone, so fail and let the caller fall back to the slow
> * path.
> */
> if (unlikely((flags & FOLL_LONGTERM) &&
> !is_pinnable_page(page))) /* which we just changed */
Specifically, the recent patch effectively acted as an error injection
test, by forcing is_pinnable_page() to always return true (if CONFIG_CMA
is defined). Because: MIGRATE_CMA|MIGRATE_ISOLATE == 7, which will match
any of the MIGRATE_* enums when checked with bitwise AND.
I suspect this particular error path has not been exercised much, or if
it has, not reported here anyway. Until now.
thanks,
--
John Hubbard
NVIDIA
next prev parent reply other threads:[~2022-05-14 2:55 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-13 9:03 [syzbot] WARNING in follow_hugetlb_page syzbot
2022-05-13 16:43 ` syzbot
2022-05-13 17:26 ` Andrew Morton
2022-05-13 18:09 ` Mike Kravetz
2022-05-13 22:48 ` Mike Kravetz
2022-05-13 23:19 ` Andrew Morton
2022-05-13 23:54 ` Minchan Kim
2022-05-14 0:09 ` John Hubbard
2022-05-14 0:26 ` Minchan Kim
2022-05-14 0:56 ` John Hubbard
2022-05-14 1:16 ` John Hubbard [this message]
2022-05-17 3:37 ` Mike Kravetz
2022-05-18 7:12 ` John Hubbard
2022-05-20 22:19 ` Minchan Kim
2022-05-20 22:56 ` John Hubbard
2022-05-20 23:25 ` Minchan Kim
2022-05-20 23:31 ` Mike Kravetz
2022-05-20 23:43 ` Minchan Kim
2022-05-21 0:04 ` Mike Kravetz
2022-05-21 15:24 ` Minchan Kim
2022-05-21 15:51 ` David Hildenbrand
2022-05-21 16:36 ` Minchan Kim
2022-05-21 16:46 ` David Hildenbrand
2022-05-21 18:25 ` Minchan Kim
2022-05-21 23:50 ` Mike Kravetz
2022-05-14 0:18 ` Andrew Morton
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