From: "Huang\, Ying" <ying.huang@intel.com>
To: Rafael Aquini <aquini@redhat.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
akpm@linux-foundation.org
Subject: Re: [PATCH] mm: swapfile: avoid split_swap_cluster() NULL pointer dereference
Date: Fri, 09 Oct 2020 08:18:10 +0800 [thread overview]
Message-ID: <877ds09rr1.fsf@yhuang-dev.intel.com> (raw)
In-Reply-To: <20201005133907.GE1530324@optiplex-lnx> (Rafael Aquini's message of "Mon, 5 Oct 2020 09:39:07 -0400")
Rafael Aquini <aquini@redhat.com> writes:
> On Thu, Oct 01, 2020 at 10:31:57AM -0400, Rafael Aquini wrote:
>> On Fri, Sep 25, 2020 at 11:21:58AM +0800, Huang, Ying wrote:
>> > Rafael Aquini <aquini@redhat.com> writes:
>> > >> Or, can you help to run the test with a debug kernel based on upstream
>> > >> kernel. I can provide some debug patch.
>> > >>
>> > >
>> > > Sure, I can set your patches to run with the test cases we have that tend to
>> > > reproduce the issue with some degree of success.
>> >
>> > Thanks!
>> >
>> > I found a race condition. During THP splitting, "head" may be unlocked
>> > before calling split_swap_cluster(), because head != page during
>> > deferred splitting. So we should call split_swap_cluster() before
>> > unlocking. The debug patch to do that is as below. Can you help to
>> > test it?
>> >
>> > Best Regards,
>> > Huang, Ying
>> >
>> > ------------------------8<----------------------------
>> > From 24ce0736a9f587d2dba12f12491c88d3e296a491 Mon Sep 17 00:00:00 2001
>> > From: Huang Ying <ying.huang@intel.com>
>> > Date: Fri, 25 Sep 2020 11:10:56 +0800
>> > Subject: [PATCH] dbg: Call split_swap_clsuter() before unlock page during
>> > split THP
>> >
>> > ---
>> > mm/huge_memory.c | 13 +++++++------
>> > 1 file changed, 7 insertions(+), 6 deletions(-)
>> >
>> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> > index faadc449cca5..8d79e5e6b46e 100644
>> > --- a/mm/huge_memory.c
>> > +++ b/mm/huge_memory.c
>> > @@ -2444,6 +2444,12 @@ static void __split_huge_page(struct page *page, struct list_head *list,
>> >
>> > remap_page(head);
>> >
>> > + if (PageSwapCache(head)) {
>> > + swp_entry_t entry = { .val = page_private(head) };
>> > +
>> > + split_swap_cluster(entry);
>> > + }
>> > +
>> > for (i = 0; i < HPAGE_PMD_NR; i++) {
>> > struct page *subpage = head + i;
>> > if (subpage == page)
>> > @@ -2678,12 +2684,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
>> > }
>> >
>> > __split_huge_page(page, list, end, flags);
>> > - if (PageSwapCache(head)) {
>> > - swp_entry_t entry = { .val = page_private(head) };
>> > -
>> > - ret = split_swap_cluster(entry);
>> > - } else
>> > - ret = 0;
>> > + ret = 0;
>> > } else {
>> > if (IS_ENABLED(CONFIG_DEBUG_VM) && mapcount) {
>> > pr_alert("total_mapcount: %u, page_count(): %u\n",
>> > --
>> > 2.28.0
>> >
>>
>> I left it running for several days, on several systems that had seen the
>> crash hitting before, and no crashes were observed for either the upstream
>> kernel nor the distro build 4.18-based kernel.
>>
>> I guess we can comfortably go with your patch. Thanks!
>>
>>
> Ping
>
> Are you going to post this patchfix soon? Or do you rather have me
> posting it?
Sorry for late replying. I just come back from a long local holiday.
Thanks a lot for testing! I will prepare the formal fixing patch.
Best Regards,
Huang, Ying
prev parent reply other threads:[~2020-10-09 0:18 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-22 18:48 [PATCH] mm: swapfile: avoid split_swap_cluster() NULL pointer dereference Rafael Aquini
2020-09-22 19:47 ` Andrew Morton
2020-09-23 13:42 ` Rafael Aquini
2020-09-25 2:59 ` Andrew Morton
2020-09-25 3:06 ` Huang, Ying
2020-09-25 3:10 ` Andrew Morton
2020-09-23 2:21 ` Huang, Ying
2020-09-23 4:34 ` Rafael Aquini
2020-09-23 5:13 ` Huang, Ying
2020-09-23 13:01 ` Rafael Aquini
2020-09-24 0:59 ` Huang, Ying
2020-09-24 2:09 ` Rafael Aquini
2020-09-24 3:51 ` Huang, Ying
2020-09-24 6:30 ` Rafael Aquini
2020-09-24 6:57 ` Huang, Ying
2020-09-24 7:45 ` Huang, Ying
2020-09-24 15:08 ` Rafael Aquini
2020-09-25 3:21 ` Huang, Ying
2020-09-26 15:16 ` Rafael Aquini
2020-09-27 5:33 ` Huang, Ying
2020-10-01 14:31 ` Rafael Aquini
2020-10-05 13:39 ` Rafael Aquini
2020-10-09 0:18 ` Huang, Ying [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=877ds09rr1.fsf@yhuang-dev.intel.com \
--to=ying.huang@intel.com \
--cc=akpm@linux-foundation.org \
--cc=aquini@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).