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Tue, 01 Sep 2020 11:37:41 -0700 (PDT) Date: Tue, 1 Sep 2020 11:37:41 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Pavel Tatashin cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, mhocko@suse.com, linux-mm@kvack.org Subject: Re: [PATCH] mm/memory_hotplug: drain per-cpu pages again during memory offline In-Reply-To: <20200901124615.137200-1-pasha.tatashin@soleen.com> Message-ID: References: <20200901124615.137200-1-pasha.tatashin@soleen.com> User-Agent: Alpine 2.23 (DEB 453 2020-06-18) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Rspamd-Queue-Id: 4F8C8180D0184 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: On Tue, 1 Sep 2020, Pavel Tatashin wrote: > There is a race during page offline that can lead to infinite loop: > a page never ends up on a buddy list and __offline_pages() keeps > retrying infinitely or until a termination signal is received. > > Thread#1 - a new process: > > load_elf_binary > begin_new_exec > exec_mmap > mmput > exit_mmap > tlb_finish_mmu > tlb_flush_mmu > release_pages > free_unref_page_list > free_unref_page_prepare > set_pcppage_migratetype(page, migratetype); > // Set page->index migration type below MIGRATE_PCPTYPES > > Thread#2 - hot-removes memory > __offline_pages > start_isolate_page_range > set_migratetype_isolate > set_pageblock_migratetype(page, MIGRATE_ISOLATE); > Set migration type to MIGRATE_ISOLATE-> set > drain_all_pages(zone); > // drain per-cpu page lists to buddy allocator. > > Thread#1 - continue > free_unref_page_commit > migratetype = get_pcppage_migratetype(page); > // get old migration type > list_add(&page->lru, &pcp->lists[migratetype]); > // add new page to already drained pcp list > > Thread#2 > Never drains pcp again, and therefore gets stuck in the loop. > > The fix is to try to drain per-cpu lists again after > check_pages_isolated_cb() fails. > > Signed-off-by: Pavel Tatashin > Cc: stable@vger.kernel.org Acked-by: David Rientjes