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[172.10.233.147]) by smtp.gmail.com with ESMTPSA id h189sm209731oif.10.2020.06.10.13.49.14 (version=TLS1 cipher=ECDHE-ECDSA-AES128-SHA bits=128/128); Wed, 10 Jun 2020 13:49:14 -0700 (PDT) Date: Wed, 10 Jun 2020 13:48:59 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Mel Gorman cc: Andrew Morton , Vlastimil Babka , Li Wang , Alex Shi , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH] mm, page_alloc: capture page in task context only Message-ID: User-Agent: Alpine 2.11 (LSU 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Rspamd-Queue-Id: 75BFF1696C X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam04 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: While stressing compaction, one run oopsed on NULL capc->cc in __free_one_page()'s task_capc(zone): compact_zone_order() had been interrupted, and a page was being freed in the return from interrupt. Though you would not expect it from the source, both gccs I was using (a 4.8.1 and a 7.5.0) had chosen to compile compact_zone_order() with the ".cc = &cc" implemented by mov %rbx,-0xb0(%rbp) immediately before callq compact_zone - long after the "current->capture_control = &capc". An interrupt in between those finds capc->cc NULL (zeroed by an earlier rep stos). This could presumably be fixed by a barrier() before setting current->capture_control in compact_zone_order(); but would also need more care on return from compact_zone(), in order not to risk leaking a page captured by interrupt just before capture_control is reset. Maybe that is the preferable fix, but I felt safer for task_capc() to exclude the rather surprising possibility of capture at interrupt time. Fixes: 5e1f0f098b46 ("mm, compaction: capture a page under direct compaction") Cc: stable@vger.kernel.org # 5.1+ Signed-off-by: Hugh Dickins --- mm/page_alloc.c | 1 + 1 file changed, 1 insertion(+) --- 5.8-rc0/mm/page_alloc.c 2020-06-08 14:38:47.298625588 -0700 +++ linux/mm/page_alloc.c 2020-06-10 12:12:34.982950441 -0700 @@ -814,6 +814,7 @@ static inline struct capture_control *ta struct capture_control *capc = current->capture_control; return capc && + in_task() && !(current->flags & PF_KTHREAD) && !capc->page && capc->cc->zone == zone &&