From: Matthew Wilcox <willy@infradead.org>
To: Hugh Dickins <hughd@google.com>
Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>,
Andrew Morton <akpm@linux-foundation.org>,
Andi Kleen <ak@linux.intel.com>, Christoph Lameter <cl@linux.com>,
Mike Kravetz <mike.kravetz@oracle.com>,
David Hildenbrand <david@redhat.com>,
Suren Baghdasaryan <surenb@google.com>,
Yang Shi <shy828301@gmail.com>,
Sidhartha Kumar <sidhartha.kumar@oracle.com>,
Vishal Moola <vishal.moola@gmail.com>,
Kefeng Wang <wangkefeng.wang@huawei.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Tejun Heo <tj@kernel.org>,
Mel Gorman <mgorman@techsingularity.net>,
Michal Hocko <mhocko@suse.com>,
"Huang, Ying" <ying.huang@intel.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH] mempolicy: migration attempt to match interleave nodes: fix
Date: Tue, 24 Oct 2023 17:45:12 +0100 [thread overview]
Message-ID: <ZTf0mP3fTvhlr/DX@casper.infradead.org> (raw)
In-Reply-To: <5b570bcd-e0fb-4473-7cfc-81b8b53d7712@google.com>
On Tue, Oct 24, 2023 at 09:32:44AM -0700, Hugh Dickins wrote:
> On Tue, 24 Oct 2023, Liam R. Howlett wrote:
>
> > * Hugh Dickins <hughd@google.com> [231024 02:50]:
> > > mm-unstable commit edd33b8807a1 ("mempolicy: migration attempt to match
> > > interleave nodes") added a second vma_iter search to do_mbind(), to
> > > determine the interleave index to be used in the MPOL_INTERLEAVE case.
> > >
> > > But sadly it added it just after the mmap_write_unlock(), leaving this
> > > new VMA search unprotected: and so syzbot reports suspicious RCU usage
> > > from lib/maple_tree.c:856.
> > >
> > > This could be fixed with an rcu_read_lock/unlock() pair (per Liam);
> > > but since we have been relying on the mmap_lock up to this point, it's
> > > slightly better to extend it over the new search too, for a well-defined
> > > result consistent with the policy this mbind() is establishing (rather
> > > than whatever might follow once the mmap_lock is dropped).
> >
> > Would downgrading the lock work? It would avoid the potential writing
> > issue and should still satisfy lockdep.
>
> Downgrading the lock would work, but it would be a pointless complication.
I tend to agree. It's also becoming far less important these days
with the vast majority of page faults handled under the per-VMA lock.
We might be able to turn it into a mutex instead of an rwsem without
seeing a noticable drop-off in performance. Not volunteering to try this.
prev parent reply other threads:[~2023-10-24 16:46 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-03 9:12 [PATCH v2 00/12] mempolicy: cleanups leading to NUMA mpol without vma Hugh Dickins
2023-10-03 9:15 ` [PATCH v2 01/12] hugetlbfs: drop shared NUMA mempolicy pretence Hugh Dickins
2023-10-03 9:16 ` [PATCH v2 02/12] kernfs: drop shared NUMA mempolicy hooks Hugh Dickins
2023-10-03 9:17 ` [PATCH v2 03/12] mempolicy: fix migrate_pages(2) syscall return nr_failed Hugh Dickins
2023-10-07 7:27 ` Huang, Ying
2023-10-03 9:19 ` [PATCH v2 04/12] mempolicy trivia: delete those ancient pr_debug()s Hugh Dickins
2023-10-03 9:20 ` [PATCH v2 05/12] mempolicy trivia: slightly more consistent naming Hugh Dickins
2023-10-03 9:21 ` [PATCH v2 06/12] mempolicy trivia: use pgoff_t in shared mempolicy tree Hugh Dickins
2023-10-03 9:22 ` [PATCH v2 07/12] mempolicy: mpol_shared_policy_init() without pseudo-vma Hugh Dickins
2023-10-03 9:24 ` [PATCH v2 08/12] mempolicy: remove confusing MPOL_MF_LAZY dead code Hugh Dickins
2023-10-03 22:28 ` Yang Shi
2023-10-03 9:25 ` [PATCH v2 09/12] mm: add page_rmappable_folio() wrapper Hugh Dickins
2023-10-03 9:26 ` [PATCH v2 10/12] mempolicy: alloc_pages_mpol() for NUMA policy without vma Hugh Dickins
2023-10-19 20:39 ` [PATCH v3 " Hugh Dickins
2023-10-23 16:53 ` domenico cerasuolo
2023-10-23 17:53 ` Andrew Morton
2023-10-23 18:10 ` domenico cerasuolo
2023-10-23 19:05 ` Johannes Weiner
2023-10-23 19:48 ` Hugh Dickins
2023-10-24 6:44 ` [PATCH] mempolicy: alloc_pages_mpol() for NUMA policy without vma: fix Hugh Dickins
2023-10-24 8:17 ` kernel test robot
2023-10-24 15:56 ` Hugh Dickins
2023-10-24 16:09 ` [PATCH v2] " Hugh Dickins
2023-10-23 18:34 ` [PATCH v3 10/12] mempolicy: alloc_pages_mpol() for NUMA policy without vma Zi Yan
2023-10-23 21:10 ` Hugh Dickins
2023-10-23 21:13 ` Zi Yan
2023-10-03 9:27 ` [PATCH v2 11/12] mempolicy: mmap_lock is not needed while migrating folios Hugh Dickins
2023-10-03 9:29 ` [PATCH v2 12/12] mempolicy: migration attempt to match interleave nodes Hugh Dickins
2023-10-24 6:50 ` [PATCH] mempolicy: migration attempt to match interleave nodes: fix Hugh Dickins
2023-10-24 15:18 ` Liam R. Howlett
2023-10-24 16:32 ` Hugh Dickins
2023-10-24 16:45 ` Matthew Wilcox [this message]
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