From: "Vlastimil Babka (SUSE)" <vbabka@kernel.org>
To: "Gregory Price (Meta)" <gourry@gourry.net>, linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com,
muchun.song@linux.dev, osalvador@suse.de, david@kernel.org,
akpm@linux-foundation.org, ziy@nvidia.com,
joshua.hahnjy@gmail.com, rakie.kim@sk.com,
ying.huang@linux.alibaba.com, ljs@kernel.org, liam@infradead.org,
rppt@kernel.org, surenb@google.com, mhocko@suse.com,
brendan.jackman@linux.dev, hannes@cmpxchg.org,
mgorman@techsingularity.net, anshuman.khandual@arm.com,
stable@vger.kernel.org
Subject: Re: [PATCH v4 3/8] mm/page_alloc: snapshot the preferred zone against shrink rebuilds
Date: Thu, 29 Oct 2026 16:21:31 +0100 [thread overview]
Message-ID: <de5cfd94-279d-4640-95ab-97f44b6b9841@kernel.org> (raw)
In-Reply-To: <20261028211930.3504634-4-gourry@gourry.net>
On 10/28/26 22:19, Gregory Price (Meta) wrote:
> get_page_from_freelist() and alloc_pages_bulk_noprof() reread
> ac->preferred_zoneref->zone at every use. Offlining a zone's last block
> rebuilds the zonelists in place, and the shrunk list's NULL terminator
> can land on the preferred slot mid-walk:
>
> CPU 0 CPU 1
> get_page_from_freelist(GFP_KERNEL | __GFP_THISNODE)
> zone = NORMAL (slot 1)
> offline_pages()
> build_all_zonelists()
> [MOVABLE, NORMAL, NULL]
> -> [NORMAL, NULL]
> rmqueue(zonelist_zone(slot 1), zone)
> zone_statistics(NULL, zone)
>
> BUG: kernel NULL pointer dereference, address: 0000000000000060
> RIP: 0010:get_page_from_freelist+0x6a5/0x15f0
> Call Trace:
> __alloc_frozen_pages_noprof+0x125/0x330
>
> Read the slot once. Zones are never freed, so a stale zone is safe, and
> a NULL slot fails the same way as walking off the end.
>
> Fixes: 11cd8638c37f ("mm, page_alloc: remove stop_machine from build_all_zonelists")
> Cc: stable@vger.kernel.org
> Signed-off-by: Gregory Price (Meta) <gourry@gourry.net>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
next prev parent reply other threads:[~2026-10-29 15:29 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-28 21:19 [PATCH v4 0/8] mm: fix allocator races with memory hotplug Gregory Price (Meta)
2026-10-28 21:19 ` [PATCH v4 1/8] mm/page_alloc: reset can_retry_reserves when the slowpath restarts Gregory Price (Meta)
2026-10-29 13:37 ` Vlastimil Babka (SUSE)
2026-10-29 16:31 ` Gregory Price (Meta)
2026-10-28 21:19 ` [PATCH v4 2/8] mm/page_alloc: detect zonelist rebuilds from memory hot-add Gregory Price (Meta)
2026-10-28 21:19 ` [PATCH v4 3/8] mm/page_alloc: snapshot the preferred zone against shrink rebuilds Gregory Price (Meta)
2026-10-29 15:21 ` Vlastimil Babka (SUSE) [this message]
2026-10-28 21:19 ` [PATCH v4 4/8] mm/mmzone: read each zoneref slot once when filtering by nodemask Gregory Price (Meta)
2026-10-29 15:51 ` Vlastimil Babka (SUSE)
2026-10-28 21:19 ` [PATCH v4 5/8] mm/page_alloc: retry allocations that raced with a zonelist rebuild Gregory Price (Meta)
2026-10-29 17:47 ` Vlastimil Babka (SUSE)
2026-10-28 21:19 ` [PATCH v4 6/8] mm/hugetlb: retry the pool walk when the zonelist is rebuilt Gregory Price (Meta)
2026-10-29 18:08 ` Vlastimil Babka (SUSE)
2026-10-30 1:37 ` Gregory Price (Meta)
2026-10-28 21:19 ` [PATCH v4 7/8] mm/page_alloc: retry alloc_contig_pages() " Gregory Price (Meta)
2026-10-29 18:10 ` Vlastimil Babka (SUSE)
2026-10-28 21:19 ` [PATCH v4 8/8] mm/mempolicy: read the zoneref slot once in mempolicy_slab_node() Gregory Price (Meta)
2026-10-29 18:16 ` Vlastimil Babka (SUSE)
2026-10-29 21:19 ` sashiko-bot
2026-10-29 18:52 ` [PATCH v4 0/8] mm: fix allocator races with memory hotplug Gregory Price (Meta)
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