From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com ([217.140.101.70]:32788 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1035659AbdEZOwX (ORCPT ); Fri, 26 May 2017 10:52:23 -0400 From: Punit Agrawal To: Mel Gorman Cc: , , , , , , , Subject: Re: + mm-migrate-fix-ref-count-handling-when-hugepage_migration_supported-v2.patch added to -mm tree References: <59275ebf.J2Z9kk9uuHWKdJS8%akpm@linux-foundation.org> <20170526104239.d2dwmm3vdcjx2g5n@techsingularity.net> Date: Fri, 26 May 2017 15:52:21 +0100 In-Reply-To: <20170526104239.d2dwmm3vdcjx2g5n@techsingularity.net> (Mel Gorman's message of "Fri, 26 May 2017 11:42:39 +0100") Message-ID: <87bmqfd61m.fsf@e105922-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain Sender: stable-owner@vger.kernel.org List-ID: Mel Gorman writes: > On Thu, May 25, 2017 at 03:46:23PM -0700, akpm@linux-foundation.org wrote: >> ------------------------------------------------------ >> From: Punit Agrawal >> Subject: mm/migrate: fix refcount handling when !hugepage_migration_supported() >> >> On failing to migrate a page, soft_offline_huge_page() performs the >> necessary update to the hugepage ref-count. When >> !hugepage_migration_supported() , unmap_and_move_hugepage() also >> decrements the page ref-count for the hugepage. The combined behaviour >> leaves the ref-count in an inconsistent state. >> >> This leads to soft lockups when running the overcommitted hugepage test >> from mce-tests suite. >> >> Soft offlining pfn 0x83ed600 at process virtual address 0x400000000000 >> soft offline: 0x83ed600: migration failed 1, type >> 1fffc00000008008 (uptodate|head) >> INFO: rcu_preempt detected stalls on CPUs/tasks: >> Tasks blocked on level-0 rcu_node (CPUs 0-7): P2715 >> (detected by 7, t=5254 jiffies, g=963, c=962, q=321) >> thugetlb_overco R running task 0 2715 2685 0x00000008 >> Call trace: >> [] dump_backtrace+0x0/0x268 >> [] show_stack+0x24/0x30 >> [] sched_show_task+0x134/0x180 >> [] rcu_print_detail_task_stall_rnp+0x54/0x7c >> [] rcu_check_callbacks+0xa74/0xb08 >> [] update_process_times+0x34/0x60 >> [] tick_sched_handle.isra.7+0x38/0x70 >> [] tick_sched_timer+0x4c/0x98 >> [] __hrtimer_run_queues+0xc0/0x300 >> [] hrtimer_interrupt+0xac/0x228 >> [] arch_timer_handler_phys+0x3c/0x50 >> [] handle_percpu_devid_irq+0x8c/0x290 >> [] generic_handle_irq+0x34/0x50 >> [] __handle_domain_irq+0x68/0xc0 >> [] gic_handle_irq+0x5c/0xb0 >> >> Address this by changing the putback_active_hugepage() in >> soft_offline_huge_page() to putback_movable_pages(). >> > > I've never looked too closely at how hardware poisoning and hugetlb pages > migration is handled so I could easily have missed something but this > changelog and patch confuses me. > > Surely if the inconsistency is between hugepage_migration_supported and > !hugepage_migration_supported then the check in soft_offline_huge_page() > should also be related to hugepage_migration_supported either in > soft_offline_huge_page() or in putback_movable_pages()? The first version of the patch did indeed make a change that was around !hugepage_migration_supported() [0] which was effectively a revert of 32665f2bbfed ("mm/migrate: correct failure handling if !hugepage_migration_support()"). But Horiguchi-san suggested that dropping the putback_active_hugepage() from unmap_and_move_hugepage() will bring back the issue that 32665f2bbfed addressed it was safer to take the current approach. It also matches the pattern followed for !hugepage. I did update the changelog but perhaps not enough - would updating the changelog to reflect this help make it clearer? Thanks, Punit [0] https://www.spinics.net/lists/kernel/msg2516334.html