From: Baoquan He <bhe@redhat.com>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: linux-mm@kvack.org, akpm@linux-foundation.org,
linux-kernel@vger.kernel.org, mpe@ellerman.id.au,
linuxppc-dev@lists.ozlabs.org,
Sachin Sant <sachinp@linux.vnet.ibm.com>,
dan.j.williams@intel.com, mhocko@kernel.org, david@redhat.com
Subject: Re: [PATCH] mm/sparse: Fix kernel crash with pfn_section_valid check
Date: Wed, 25 Mar 2020 16:36:37 +0800 [thread overview]
Message-ID: <20200325083637.GJ3039@MiWiFi-R3L-srv> (raw)
In-Reply-To: <5cdf5334-7fbb-8427-1918-ed67d5f23834@linux.ibm.com>
On 03/25/20 at 01:42pm, Aneesh Kumar K.V wrote:
> On 3/25/20 1:07 PM, Baoquan He wrote:
> > On 03/25/20 at 03:06pm, Baoquan He wrote:
> > > On 03/25/20 at 08:49am, Aneesh Kumar K.V wrote:
> >
> > > > mm/sparse.c | 2 ++
> > > > 1 file changed, 2 insertions(+)
> > > >
> > > > diff --git a/mm/sparse.c b/mm/sparse.c
> > > > index aadb7298dcef..3012d1f3771a 100644
> > > > --- a/mm/sparse.c
> > > > +++ b/mm/sparse.c
> > > > @@ -781,6 +781,8 @@ static void section_deactivate(unsigned long pfn, unsigned long nr_pages,
> > > > ms->usage = NULL;
> > > > }
> > > > memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr);
> > > > + /* Mark the section invalid */
> > > > + ms->section_mem_map &= ~SECTION_HAS_MEM_MAP;
> > >
> > > Not sure if we should add checking in valid_section() or pfn_valid(),
> > > e.g check ms->usage validation too. Otherwise, this fix looks good to
> > > me.
> >
> > With SPASEMEM_VMEMAP enabled, we should do validation check on ms->usage
> > before checking any subsection is valid. Since now we do have case
> > in which ms->usage is released, people still try to check it.
> >
> > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> > index f0a2c184eb9a..d79bd938852e 100644
> > --- a/include/linux/mmzone.h
> > +++ b/include/linux/mmzone.h
> > @@ -1306,6 +1306,8 @@ static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn)
> > {
> > int idx = subsection_map_index(pfn);
> > + if (!ms->usage)
> > + return 0;
> > return test_bit(idx, ms->usage->subsection_map);
> > }
> > #else
> >
>
> We always check for section valid, before we check if pfn_section_valid().
>
> static inline int pfn_valid(unsigned long pfn)
>
> struct mem_section *ms;
>
> if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
> return 0;
> ms = __nr_to_section(pfn_to_section_nr(pfn));
> if (!valid_section(ms))
> return 0;
> /*
> * Traditionally early sections always returned pfn_valid() for
> * the entire section-sized span.
> */
> return early_section(ms) || pfn_section_valid(ms, pfn);
> }
>
>
> IMHO adding that if (!ms->usage) is redundant.
Yeah, I tend to agree. Consider this happens in the only small window
between ms->usage releasing and ms->section_mem_map releasing when
removing a section. Just thought adding this check to enhance it even
though we have had your fix, because we only check ms->section_mem_map
in valid_section(). Anyway, your fix looks good to me, see if other
people have any comment.
Thanks
Baoquan
next prev parent reply other threads:[~2020-03-25 8:36 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-25 3:19 [PATCH] mm/sparse: Fix kernel crash with pfn_section_valid check Aneesh Kumar K.V
2020-03-25 7:06 ` Baoquan He
2020-03-25 7:37 ` Baoquan He
2020-03-25 8:12 ` Aneesh Kumar K.V
2020-03-25 8:36 ` Baoquan He [this message]
2020-03-26 0:38 ` Andrew Morton
2020-03-26 9:40 ` Michal Hocko
2020-03-26 9:56 ` Aneesh Kumar K.V
2020-03-26 10:16 ` Michal Hocko
2020-03-26 10:50 ` Michal Hocko
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