From: Michal Hocko <mhocko@suse.com>
To: Muchun Song <songmuchun@bytedance.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>,
Andrew Morton <akpm@linux-foundation.org>,
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
Andi Kleen <ak@linux.intel.com>,
Linux Memory Management List <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [External] Re: [PATCH v2 3/6] mm: hugetlb: fix a race between freeing and dissolving the page
Date: Fri, 8 Jan 2021 12:44:11 +0100 [thread overview]
Message-ID: <20210108114411.GZ13207@dhcp22.suse.cz> (raw)
In-Reply-To: <CAMZfGtXhMDjw=C8XBUwsQLD7ZLv5osoLWy+RJzqY11WFm07GwQ@mail.gmail.com>
On Fri 08-01-21 18:08:57, Muchun Song wrote:
> On Fri, Jan 8, 2021 at 5:31 PM Michal Hocko <mhocko@suse.com> wrote:
> >
> > On Fri 08-01-21 17:01:03, Muchun Song wrote:
> > > On Fri, Jan 8, 2021 at 4:43 PM Michal Hocko <mhocko@suse.com> wrote:
> > > >
> > > > On Thu 07-01-21 23:11:22, Muchun Song wrote:
> > [..]
> > > > > But I find a tricky problem to solve. See free_huge_page().
> > > > > If we are in non-task context, we should schedule a work
> > > > > to free the page. We reuse the page->mapping. If the page
> > > > > is already freed by the dissolve path. We should not touch
> > > > > the page->mapping. So we need to check PageHuge().
> > > > > The check and llist_add() should be protected by
> > > > > hugetlb_lock. But we cannot do that. Right? If dissolve
> > > > > happens after it is linked to the list. We also should
> > > > > remove it from the list (hpage_freelist). It seems to make
> > > > > the thing more complex.
> > > >
> > > > I am not sure I follow you here but yes PageHuge under hugetlb_lock
> > > > should be the reliable way to check for the race. I am not sure why we
> > > > really need to care about mapping or other state.
> > >
> > > CPU0: CPU1:
> > > free_huge_page(page)
> > > if (PageHuge(page))
> > > dissolve_free_huge_page(page)
> > > spin_lock(&hugetlb_lock)
> > > update_and_free_page(page)
> > > spin_unlock(&hugetlb_lock)
> > > llist_add(page->mapping)
> > > // the mapping is corrupted
> > >
> > > The PageHuge(page) and llist_add() should be protected by
> > > hugetlb_lock. Right? If so, we cannot hold hugetlb_lock
> > > in free_huge_page() path.
> >
> > OK, I see. I completely forgot about this snowflake. I thought that
> > free_huge_page was a typo missing initial __. Anyway you are right that
> > this path needs a check as well. But I don't see why we couldn't use the
> > lock here. The lock can be held only inside the !in_task branch.
>
> Because we hold the hugetlb_lock without disable irq. So if an interrupt
> occurs after we hold the lock. And we also free a HugeTLB page. Then
> it leads to deadlock.
There is nothing really to prevent making hugetlb_lock irq safe, isn't
it?
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2021-01-08 11:44 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-06 8:47 [PATCH v2 0/6] Fix some bugs about HugeTLB code Muchun Song
2021-01-06 8:47 ` [PATCH v2 1/6] mm: migrate: do not migrate HugeTLB page whose refcount is one Muchun Song
2021-01-06 16:13 ` Michal Hocko
2021-01-07 2:52 ` [External] " Muchun Song
2021-01-07 11:16 ` Michal Hocko
2021-01-07 11:24 ` Muchun Song
2021-01-07 11:48 ` Michal Hocko
2021-01-06 8:47 ` [PATCH v2 2/6] mm: hugetlbfs: fix cannot migrate the fallocated HugeTLB page Muchun Song
2021-01-06 16:35 ` Michal Hocko
2021-01-06 19:30 ` Mike Kravetz
2021-01-06 20:02 ` Michal Hocko
2021-01-06 21:07 ` Mike Kravetz
2021-01-07 8:36 ` Michal Hocko
2021-01-07 2:58 ` [External] " Muchun Song
2021-01-06 8:47 ` [PATCH v2 3/6] mm: hugetlb: fix a race between freeing and dissolving the page Muchun Song
2021-01-06 16:56 ` Michal Hocko
2021-01-06 20:58 ` Mike Kravetz
2021-01-07 3:08 ` [External] " Muchun Song
2021-01-07 8:40 ` Michal Hocko
2021-01-08 0:52 ` Mike Kravetz
2021-01-08 8:28 ` Michal Hocko
2021-01-07 5:39 ` [External] " Muchun Song
2021-01-07 8:41 ` Michal Hocko
2021-01-07 8:53 ` Muchun Song
2021-01-07 11:18 ` Michal Hocko
2021-01-07 11:38 ` Muchun Song
2021-01-07 12:38 ` Michal Hocko
2021-01-07 12:59 ` Muchun Song
2021-01-07 14:11 ` Michal Hocko
2021-01-07 15:11 ` Muchun Song
2021-01-08 1:06 ` Mike Kravetz
2021-01-08 2:38 ` Muchun Song
2021-01-08 8:43 ` Michal Hocko
2021-01-08 9:01 ` Muchun Song
2021-01-08 9:31 ` Michal Hocko
2021-01-08 10:08 ` Muchun Song
2021-01-08 11:44 ` Michal Hocko [this message]
2021-01-08 11:52 ` Muchun Song
2021-01-08 12:04 ` Michal Hocko
2021-01-08 12:24 ` Muchun Song
2021-01-06 8:47 ` [PATCH v2 4/6] mm: hugetlb: add return -EAGAIN for dissolve_free_huge_page Muchun Song
2021-01-06 17:07 ` Michal Hocko
2021-01-07 3:11 ` [External] " Muchun Song
2021-01-07 8:39 ` Michal Hocko
2021-01-07 9:01 ` Muchun Song
2021-01-07 11:22 ` Michal Hocko
2021-01-06 8:47 ` [PATCH v2 5/6] mm: hugetlb: fix a race between isolating and freeing page Muchun Song
2021-01-06 17:10 ` Michal Hocko
2021-01-06 8:47 ` [PATCH v2 6/6] mm: hugetlb: remove VM_BUG_ON_PAGE from page_huge_active Muchun Song
2021-01-06 17:16 ` Michal Hocko
2021-01-08 22:24 ` Mike Kravetz
2021-01-09 4:07 ` [External] " Muchun Song
2021-01-07 9:30 ` [PATCH v2 0/6] Fix some bugs about HugeTLB code David Hildenbrand
2021-01-07 9:40 ` [External] " Muchun Song
2021-01-07 10:10 ` David Hildenbrand
2021-01-07 10:16 ` Muchun Song
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