Linux-mm Archive on lore.kernel.org
 help / color / Atom feed
From: Mina Almasry <almasrymina@google.com>
To: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Qian Cai <cai@lca.pw>, Andrew Morton <akpm@linux-foundation.org>,
	shuah <shuah@kernel.org>,  David Rientjes <rientjes@google.com>,
	Shakeel Butt <shakeelb@google.com>,
	 Greg Thelen <gthelen@google.com>,
	open list <linux-kernel@vger.kernel.org>,
	linux-mm@kvack.org,  linux-kselftest@vger.kernel.org,
	cgroups@vger.kernel.org
Subject: Re: [PATCH v12 1/9] hugetlb_cgroup: Add hugetlb_cgroup reservation counter
Date: Tue, 18 Feb 2020 14:27:57 -0800
Message-ID: <CAHS8izO0LikomAQEbGacuBfcczZXJzYWjXX1bu=hrF5ZBCT5Ng@mail.gmail.com> (raw)
In-Reply-To: <9d6690e9-0dd4-f779-89b2-e02ff9a517e4@oracle.com>

On Tue, Feb 18, 2020 at 1:41 PM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
> On 2/18/20 1:36 PM, Mina Almasry wrote:
> > On Tue, Feb 18, 2020 at 11:25 AM Mina Almasry <almasrymina@google.com> wrote:
> >>
> >> On Tue, Feb 18, 2020 at 11:14 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
> >>>
> >>> On 2/18/20 10:35 AM, Mina Almasry wrote:
> >>>> On Tue, Feb 18, 2020 at 6:21 AM Qian Cai <cai@lca.pw> wrote:
> >>>>>
> >>>>> On Tue, 2020-02-11 at 15:19 -0800, Andrew Morton wrote:
> >>>>>> On Tue, 11 Feb 2020 13:31:20 -0800 Mina Almasry <almasrymina@google.com> wrote:
> >>>>>>
> >>>>> [ 7933.806377][T14355] ------------[ cut here ]------------
> >>>>> [ 7933.806541][T14355] kernel BUG at mm/hugetlb.c:490!
> >>>>> VM_BUG_ON(t - f <= 1);
> >>>>> [ 7933.806562][T14355] Oops: Exception in kernel mode, sig: 5 [#1]
> >>> <snip>
> >>>> Hi Qian,
> >>>>
> >>>> Yes this VM_BUG_ON was added by a patch in the series ("hugetlb:
> >>>> disable region_add file_region coalescing") so it's definitely related
> >>>> to the series. I'm taking a look at why this VM_BUG_ON fires. Can you
> >>>> confirm you reproduce this by running hugemmap06 from the ltp on a
> >>>> powerpc machine? Can I maybe have your config?
> >>>>
> >>>> Thanks!
> >>>
> >>> Hi Mina,
> >>>
> >>> Looking at the region_chg code again, we do a
> >>>
> >>>         resv->adds_in_progress += *out_regions_needed;
> >>>
> >>> and then potentially drop the lock to allocate the needed entries.  Could
> >>> anopther thread (only adding reservation for a single page) then come in
> >>> and notice that there are not enough entries in the cache and hit the
> >>> VM_BUG_ON()?
> >>
> >> Maybe. Also I'm thinking the code thinks actual_regions_needed >=
> >> in_regions_needed, but that doesn't seem like a guarantee. I think
> >> this call sequence with the same t->f range would violate that:
> >>
> >> region_chg (regions_needed=1)
> >> region_chg (regions_needed=1)
> >> region_add (fills in the range)
> >> region_add (in_regions_needed = 1, actual_regions_needed = 0, so
> >> assumptions in the code break).
> >>
> >> Luckily it seems the ltp readily reproduces this, so I'm working on
> >> reproducing it. I should have a fix soon, at least if I can reproduce
> >> it as well.
> >
> > I had a bit of trouble reproducing this but I got it just now.
> >
> > Makes sense I've never run into this even though others can readily
> > reproduce it. I happen to run my kernels on a pretty beefy 36 core
> > machine and in that setup things seem to execute fast and there is
> > never a queue of pending file_region inserts into the resv_map. Once I
> > limited qemu to only use 2 cores I ran into the issue right away.
> > Looking into a fix now.
>
> This may not be optimal, but it resolves the issue for me.  I just put it
> together to test the theory that the region_chg code was at fault.

Thanks! Just sent out a similar patch "[PATCH -next] mm/hugetlb: Fix
file_region entry allocations"


  reply index

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-11 21:31 Mina Almasry
2020-02-11 21:31 ` [PATCH v12 2/9] hugetlb_cgroup: add interface for charge/uncharge hugetlb reservations Mina Almasry
2020-02-15  0:50   ` Mike Kravetz
2020-02-16  1:21     ` David Rientjes
2020-02-11 21:31 ` [PATCH v12 3/9] hugetlb_cgroup: add reservation accounting for private mappings Mina Almasry
2020-02-11 21:31 ` [PATCH v12 4/9] hugetlb: disable region_add file_region coalescing Mina Almasry
2020-02-15  1:27   ` Mike Kravetz
2020-02-16  1:25   ` David Rientjes
2020-02-11 21:31 ` [PATCH v12 5/9] hugetlb_cgroup: add accounting for shared mappings Mina Almasry
2020-02-16  1:29   ` David Rientjes
2020-02-18 18:07   ` Mike Kravetz
2020-02-11 21:31 ` [PATCH v12 6/9] hugetlb_cgroup: support noreserve mappings Mina Almasry
2020-02-18 20:57   ` Mike Kravetz
2020-02-11 21:31 ` [PATCH v12 7/9] hugetlb: support file_region coalescing again Mina Almasry
2020-02-16  1:29   ` David Rientjes
2020-02-19  3:28   ` Mike Kravetz
2020-02-19  7:54     ` Mina Almasry
2020-02-19 23:36     ` [PATCH] hugetlb: Remove check_coalesce_bug debug code Mina Almasry
2020-02-20  0:07       ` Mike Kravetz
2020-02-11 21:31 ` [PATCH v12 8/9] hugetlb_cgroup: Add hugetlb_cgroup reservation tests Mina Almasry
2020-02-12  8:50   ` Sandipan Das
2020-02-20  0:05     ` Mina Almasry
2020-02-21  0:52   ` Mike Kravetz
2020-02-11 21:31 ` [PATCH v12 9/9] hugetlb_cgroup: Add hugetlb_cgroup reservation docs Mina Almasry
2020-02-20  0:03   ` Mina Almasry
2020-02-20  0:18   ` Mike Kravetz
2020-02-11 23:19 ` [PATCH v12 1/9] hugetlb_cgroup: Add hugetlb_cgroup reservation counter Andrew Morton
2020-02-18 14:21   ` Qian Cai
2020-02-18 18:35     ` Mina Almasry
2020-02-18 18:41       ` Qian Cai
2020-02-18 19:14       ` Mike Kravetz
2020-02-18 19:25         ` Mina Almasry
2020-02-18 21:36           ` Mina Almasry
2020-02-18 21:41             ` Mike Kravetz
2020-02-18 22:27               ` Mina Almasry [this message]
2020-02-19 19:05   ` Mina Almasry
2020-02-19 21:06     ` Andrew Morton
2020-02-20 19:22       ` Mina Almasry
2020-02-21  0:28         ` Andrew Morton
2020-02-21  0:41           ` Mike Kravetz
2020-02-21  1:52             ` Mina Almasry
2020-02-21 20:19       ` Mina Almasry

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='CAHS8izO0LikomAQEbGacuBfcczZXJzYWjXX1bu=hrF5ZBCT5Ng@mail.gmail.com' \
    --to=almasrymina@google.com \
    --cc=akpm@linux-foundation.org \
    --cc=cai@lca.pw \
    --cc=cgroups@vger.kernel.org \
    --cc=gthelen@google.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-kselftest@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=mike.kravetz@oracle.com \
    --cc=rientjes@google.com \
    --cc=shakeelb@google.com \
    --cc=shuah@kernel.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

Linux-mm Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-mm/0 linux-mm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-mm linux-mm/ https://lore.kernel.org/linux-mm \
		linux-mm@kvack.org
	public-inbox-index linux-mm

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kvack.linux-mm


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git