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[91.189.89.112]) by mx.google.com with ESMTPS id f27si6147327wmi.75.2017.05.24.15.19.26 for (version=TLS1 cipher=AES128-SHA bits=128/128); Wed, 24 May 2017 15:19:26 -0700 (PDT) Date: Wed, 24 May 2017 17:19:16 -0500 (CDT) From: Manoj Iyer Subject: Re: mm/migrate: Fix ref-count handling when !hugepage_migration_supported() In-Reply-To: <20170524154728.2492-1-punit.agrawal@arm.com> Message-ID: References: <20170524154728.2492-1-punit.agrawal@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Sender: owner-linux-mm@kvack.org List-ID: To: Punit Agrawal Cc: Andrew Morton , will.deacon@arm.com, catalin.marinas@arm.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, tbaicar@codeaurora.org, "Tabi, Timur" , Joonsoo Kim , Naoya Horiguchi , Wanpeng Li , Christoph Lameter On Wed, 24 May 2017, 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 > --- > Hi Andrew, > > We ran into this bug when working towards enabling memory corruption > on arm64. The patch was tested on an arm64 platform running v4.12-rc2 > with the series to enable memory corruption handling[0]. > > Please consider merging as a fix for the 4.12 release. > > Thanks, > Punit > I applied this patch applied to Ubuntu Zesty (4.10) kernel and tested on QDF2400 platform with mce-test without config migration enabled. == dmesg == [ 91.569358] Soft offlining page 0x1763c00 at 0x400000000000 [ 91.569364] soft offline: 0x1763c00: migration failed 1, type 100000000008008 [ 150.282911] Soft offlining page 0x1763c00 at 0x400000000000 [ 150.282917] soft offline: 0x1763c00: migration failed 1, type 100000000008008 The mce-test failed as expected but did not encounter the soft lockups. (The test case might have an error it is missing an 'echo' in failure case.) $ sudo ./run_hugepage_overcommit.sh *************************************************************************** Pay attention: This test checks that hugepage soft-offlining works under overcommitting. *************************************************************************** ------------------------------------- TestCase ./thugetlb_overcommit 1 FAIL: migration failed. Unpoisoning. Num of Executed Test Case: 1 Num of Failed Case: 1 Tested-By: Manoj Iyer Thanks Manoj Iyer > [0] https://www.spinics.net/lists/arm-kernel/msg581657.html > --- > mm/migrate.c | 4 +--- > 1 file changed, 1 insertion(+), 3 deletions(-) > > diff --git a/mm/migrate.c b/mm/migrate.c > index 89a0a1707f4c..187abd1526df 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1201,10 +1201,8 @@ static int unmap_and_move_huge_page(new_page_t get_new_page, > * tables or check whether the hugepage is pmd-based or not before > * kicking migration. > */ > - if (!hugepage_migration_supported(page_hstate(hpage))) { > - putback_active_hugepage(hpage); > + if (!hugepage_migration_supported(page_hstate(hpage))) > return -ENOSYS; > - } > > new_hpage = get_new_page(hpage, private, &result); > if (!new_hpage) > -- ============================ Manoj Iyer Ubuntu/Canonical ARM Servers - Cloud ============================ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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