From: Muchun Song <songmuchun@bytedance.com>
To: Michal Hocko <mhocko@suse.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>,
Linux Memory Management List <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
Roman Gushchin <guro@fb.com>, Shakeel Butt <shakeelb@google.com>,
Oscar Salvador <osalvador@suse.de>,
David Hildenbrand <david@redhat.com>,
David Rientjes <rientjes@google.com>,
Miaohe Lin <linmiaohe@huawei.com>,
Peter Zijlstra <peterz@infradead.org>,
Matthew Wilcox <willy@infradead.org>,
HORIGUCHI NAOYA <naoya.horiguchi@nec.com>,
"Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>,
Waiman Long <longman@redhat.com>, Peter Xu <peterx@redhat.com>,
Mina Almasry <almasrymina@google.com>,
Hillf Danton <hdanton@sina.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Barry Song <song.bao.hua@hisilicon.com>,
Will Deacon <will@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [External] Re: [PATCH v2 1/8] mm/cma: change cma mutex to irq safe spinlock
Date: Tue, 30 Mar 2021 16:21:45 +0800 [thread overview]
Message-ID: <CAMZfGtWOY+gxSkfVNdW-GfKfZXKCgjwYGo=Y6ABk5L=HDsxhVg@mail.gmail.com> (raw)
In-Reply-To: <YGLe31q/4kAoLmmr@dhcp22.suse.cz>
On Tue, Mar 30, 2021 at 4:18 PM Michal Hocko <mhocko@suse.com> wrote:
>
> On Tue 30-03-21 16:08:36, Muchun Song wrote:
> > On Tue, Mar 30, 2021 at 4:01 PM Michal Hocko <mhocko@suse.com> wrote:
> > >
> > > On Mon 29-03-21 16:23:55, Mike Kravetz wrote:
> > > > Ideally, cma_release could be called from any context. However, that is
> > > > not possible because a mutex is used to protect the per-area bitmap.
> > > > Change the bitmap to an irq safe spinlock.
> > >
> > > I would phrase the changelog slightly differerent
> > > "
> > > cma_release is currently a sleepable operatation because the bitmap
> > > manipulation is protected by cma->lock mutex. Hugetlb code which relies
> > > on cma_release for CMA backed (giga) hugetlb pages, however, needs to be
> > > irq safe.
> > >
> > > The lock doesn't protect any sleepable operation so it can be changed to
> > > a (irq aware) spin lock. The bitmap processing should be quite fast in
> > > typical case but if cma sizes grow to TB then we will likely need to
> > > replace the lock by a more optimized bitmap implementation.
> > > "
> > >
> > > it seems that you are overusing irqsave variants even from context which
> > > are never called from the IRQ context so they do not need storing flags.
> > >
> > > [...]
> > > > @@ -391,8 +391,9 @@ static void cma_debug_show_areas(struct cma *cma)
> > > > unsigned long start = 0;
> > > > unsigned long nr_part, nr_total = 0;
> > > > unsigned long nbits = cma_bitmap_maxno(cma);
> > > > + unsigned long flags;
> > > >
> > > > - mutex_lock(&cma->lock);
> > > > + spin_lock_irqsave(&cma->lock, flags);
> > >
> > > spin_lock_irq should be sufficient. This is only called from the
> > > allocation context and that is never called from IRQ context.
> >
> > This makes me think more. I think that spin_lock should be
> > sufficient. Right?
>
> Nope. Think of the following scenario
> spin_lock(cma->lock);
> <IRQ>
> put_page
> __free_huge_page
> cma_release
> spin_lock_irqsave() DEADLOCK
Got it. Thanks.
> --
> Michal Hocko
> SUSE Labs
next prev parent reply other threads:[~2021-03-30 8:22 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-29 23:23 [PATCH v2 0/8] make hugetlb put_page safe for all calling contexts Mike Kravetz
2021-03-29 23:23 ` [PATCH v2 1/8] mm/cma: change cma mutex to irq safe spinlock Mike Kravetz
2021-03-30 1:13 ` Roman Gushchin
2021-03-30 1:20 ` Song Bao Hua (Barry Song)
2021-03-30 2:18 ` Mike Kravetz
2021-03-30 8:01 ` Michal Hocko
2021-03-30 8:08 ` [External] " Muchun Song
2021-03-30 8:17 ` Song Bao Hua (Barry Song)
2021-03-30 8:18 ` Michal Hocko
2021-03-30 8:21 ` Muchun Song [this message]
2021-03-31 2:37 ` Mike Kravetz
2021-03-29 23:23 ` [PATCH v2 2/8] hugetlb: no need to drop hugetlb_lock to call cma_release Mike Kravetz
2021-03-30 1:13 ` Roman Gushchin
2021-03-30 8:01 ` Michal Hocko
2021-03-29 23:23 ` [PATCH v2 3/8] hugetlb: add per-hstate mutex to synchronize user adjustments Mike Kravetz
2021-03-30 2:23 ` [External] " Muchun Song
2021-03-29 23:23 ` [PATCH v2 4/8] hugetlb: create remove_hugetlb_page() to separate functionality Mike Kravetz
2021-03-29 23:23 ` [PATCH v2 5/8] hugetlb: call update_and_free_page without hugetlb_lock Mike Kravetz
2021-03-30 2:10 ` Miaohe Lin
2021-03-30 2:21 ` [External] " Muchun Song
2021-03-31 2:39 ` Mike Kravetz
2021-03-29 23:24 ` [PATCH v2 6/8] hugetlb: change free_pool_huge_page to remove_pool_huge_page Mike Kravetz
2021-03-30 2:30 ` [External] " Muchun Song
2021-03-30 8:06 ` Michal Hocko
2021-03-29 23:24 ` [PATCH v2 7/8] hugetlb: make free_huge_page irq safe Mike Kravetz
2021-03-29 23:24 ` [PATCH v2 8/8] hugetlb: add lockdep_assert_held() calls for hugetlb_lock Mike Kravetz
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