From mboxrd@z Thu Jan 1 00:00:00 1970 From: punit.agrawal@arm.com (Punit Agrawal) Date: Thu, 25 May 2017 10:49:47 +0100 Subject: [PATCH] mm/migrate: Fix ref-count handling when !hugepage_migration_supported() In-Reply-To: <20170524125610.8fbc644f8fa1cf8175b7757b@linux-foundation.org> (Andrew Morton's message of "Wed, 24 May 2017 12:56:10 -0700") References: <20170524154728.2492-1-punit.agrawal@arm.com> <20170524125610.8fbc644f8fa1cf8175b7757b@linux-foundation.org> Message-ID: <87y3tle05g.fsf@e105922-lin.cambridge.arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Andrew Morton writes: > On Wed, 24 May 2017 16:47:28 +0100 Punit Agrawal wrote: > >> 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 >> >> Fix this by dropping the ref-count decrement in >> unmap_and_move_hugepage() when !hugepage_migration_supported(). >> >> Fixes: 32665f2bbfed ("mm/migrate: correct failure handling if !hugepage_migration_support()") >> Reported-by: Manoj Iyer >> Signed-off-by: Punit Agrawal >> Cc: Joonsoo Kim >> Cc: Naoya Horiguchi >> Cc: Wanpeng Li >> Cc: Christoph Lameter > > 32665f2bbfed was three years ago. Do you have any theory as to why > this took so long to be detected? This only triggers on systems that enable memory failure handling (ARCH_SUPPORTS_MEMORY_FAILURE) but not hugepage migration (!ARCH_ENABLE_HUGEPAGE_MIGRATION). I imagine this wasn't triggered as there aren't many systems running this configuration. > And do you believe a -stable backport is warranted? I'll defer to Horiguchi-san's judgement here. > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo at kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email at kvack.org