From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:42170 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753280AbdGCJCc (ORCPT ); Mon, 3 Jul 2017 05:02:32 -0400 Subject: Patch "mm: numa: avoid waiting on freed migrated pages" has been added to the 4.4-stable tree To: mark.rutland@arm.com, akpm@linux-foundation.org, gregkh@linuxfoundation.org, kirill.shutemov@linux.intel.com, mgorman@suse.de, steve.capper@arm.com, torvalds@linux-foundation.org, vbabka@suse.cz, will.deacon@arm.com Cc: , From: Date: Mon, 03 Jul 2017 11:02:32 +0200 Message-ID: <14990725524944@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: This is a note to let you know that I've just added the patch titled mm: numa: avoid waiting on freed migrated pages to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: mm-numa-avoid-waiting-on-freed-migrated-pages.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >>From 3c226c637b69104f6b9f1c6ec5b08d7b741b3229 Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Fri, 16 Jun 2017 14:02:34 -0700 Subject: mm: numa: avoid waiting on freed migrated pages From: Mark Rutland commit 3c226c637b69104f6b9f1c6ec5b08d7b741b3229 upstream. In do_huge_pmd_numa_page(), we attempt to handle a migrating thp pmd by waiting until the pmd is unlocked before we return and retry. However, we can race with migrate_misplaced_transhuge_page(): // do_huge_pmd_numa_page // migrate_misplaced_transhuge_page() // Holds 0 refs on page // Holds 2 refs on page vmf->ptl = pmd_lock(vma->vm_mm, vmf->pmd); /* ... */ if (pmd_trans_migrating(*vmf->pmd)) { page = pmd_page(*vmf->pmd); spin_unlock(vmf->ptl); ptl = pmd_lock(mm, pmd); if (page_count(page) != 2)) { /* roll back */ } /* ... */ mlock_migrate_page(new_page, page); /* ... */ spin_unlock(ptl); put_page(page); put_page(page); // page freed here wait_on_page_locked(page); goto out; } This can result in the freed page having its waiters flag set unexpectedly, which trips the PAGE_FLAGS_CHECK_AT_PREP checks in the page alloc/free functions. This has been observed on arm64 KVM guests. We can avoid this by having do_huge_pmd_numa_page() take a reference on the page before dropping the pmd lock, mirroring what we do in __migration_entry_wait(). When we hit the race, migrate_misplaced_transhuge_page() will see the reference and abort the migration, as it may do today in other cases. Fixes: b8916634b77bffb2 ("mm: Prevent parallel splits during THP migration") Link: http://lkml.kernel.org/r/1497349722-6731-2-git-send-email-will.deacon@arm.com Signed-off-by: Mark Rutland Signed-off-by: Will Deacon Acked-by: Steve Capper Acked-by: Kirill A. Shutemov Acked-by: Vlastimil Babka Cc: Mel Gorman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- mm/huge_memory.c | 6 ++++++ 1 file changed, 6 insertions(+) --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1363,8 +1363,11 @@ int do_huge_pmd_numa_page(struct mm_stru */ if (unlikely(pmd_trans_migrating(*pmdp))) { page = pmd_page(*pmdp); + if (!get_page_unless_zero(page)) + goto out_unlock; spin_unlock(ptl); wait_on_page_locked(page); + put_page(page); goto out; } @@ -1396,8 +1399,11 @@ int do_huge_pmd_numa_page(struct mm_stru /* Migration could have started since the pmd_trans_migrating check */ if (!page_locked) { + if (!get_page_unless_zero(page)) + goto out_unlock; spin_unlock(ptl); wait_on_page_locked(page); + put_page(page); page_nid = -1; goto out; } Patches currently in stable-queue which might be from mark.rutland@arm.com are queue-4.4/mm-numa-avoid-waiting-on-freed-migrated-pages.patch