From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f197.google.com (mail-pf0-f197.google.com [209.85.192.197]) by kanga.kvack.org (Postfix) with ESMTP id 9FDBA6B0279 for ; Mon, 17 Jul 2017 21:12:20 -0400 (EDT) Received: by mail-pf0-f197.google.com with SMTP id y62so6726481pfa.3 for ; Mon, 17 Jul 2017 18:12:20 -0700 (PDT) Received: from EX13-EDG-OU-001.vmware.com (ex13-edg-ou-001.vmware.com. [208.91.0.189]) by mx.google.com with ESMTPS id x32si571773pld.52.2017.07.17.18.12.19 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Mon, 17 Jul 2017 18:12:19 -0700 (PDT) From: Nadav Amit Subject: [PATCH] mm: Prevent racy access to tlb_flush_pending Date: Mon, 17 Jul 2017 11:02:46 -0700 Message-ID: <20170717180246.62277-1-namit@vmware.com> MIME-Version: 1.0 Content-Type: text/plain Sender: owner-linux-mm@kvack.org List-ID: To: linux-mm@kvack.org Cc: nadav.amit@gmail.com, mgorman@suse.de, riel@redhat.com, luto@kernel.org, Nadav Amit Setting and clearing mm->tlb_flush_pending can be performed by multiple threads, since mmap_sem may only be acquired for read in task_numa_work. If this happens, tlb_flush_pending may be cleared while one of the threads still changes PTEs and batches TLB flushes. As a result, TLB flushes can be skipped because the indication of pending TLB flushes is lost, for instance due to race between migration and change_protection_range (just as in the scenario that caused the introduction of tlb_flush_pending). The feasibility of such a scenario was confirmed by adding assertion to check tlb_flush_pending is not set by two threads, adding artificial latency in change_protection_range() and using sysctl to reduce kernel.numa_balancing_scan_delay_ms. Fixes: 20841405940e ("mm: fix TLB flush race between migration, and change_protection_range") Signed-off-by: Nadav Amit --- include/linux/mm_types.h | 8 ++++---- kernel/fork.c | 2 +- mm/debug.c | 2 +- 3 files changed, 6 insertions(+), 6 deletions(-) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 45cdb27791a3..36f4ec589544 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -493,7 +493,7 @@ struct mm_struct { * can move process memory needs to flush the TLB when moving a * PROT_NONE or PROT_NUMA mapped page. */ - bool tlb_flush_pending; + atomic_t tlb_flush_pending; #endif struct uprobes_state uprobes_state; #ifdef CONFIG_HUGETLB_PAGE @@ -528,11 +528,11 @@ static inline cpumask_t *mm_cpumask(struct mm_struct *mm) static inline bool mm_tlb_flush_pending(struct mm_struct *mm) { barrier(); - return mm->tlb_flush_pending; + return atomic_read(&mm->tlb_flush_pending) > 0; } static inline void set_tlb_flush_pending(struct mm_struct *mm) { - mm->tlb_flush_pending = true; + atomic_inc(&mm->tlb_flush_pending); /* * Guarantee that the tlb_flush_pending store does not leak into the @@ -544,7 +544,7 @@ static inline void set_tlb_flush_pending(struct mm_struct *mm) static inline void clear_tlb_flush_pending(struct mm_struct *mm) { barrier(); - mm->tlb_flush_pending = false; + atomic_dec(&mm->tlb_flush_pending); } #else static inline bool mm_tlb_flush_pending(struct mm_struct *mm) diff --git a/kernel/fork.c b/kernel/fork.c index e53770d2bf95..5a7ecfbb7420 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -809,7 +809,7 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p, mm_init_aio(mm); mm_init_owner(mm, p); mmu_notifier_mm_init(mm); - clear_tlb_flush_pending(mm); + atomic_set(&mm->tlb_flush_pending, 0); #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS mm->pmd_huge_pte = NULL; #endif diff --git a/mm/debug.c b/mm/debug.c index db1cd26d8752..d70103bb4731 100644 --- a/mm/debug.c +++ b/mm/debug.c @@ -159,7 +159,7 @@ void dump_mm(const struct mm_struct *mm) mm->numa_next_scan, mm->numa_scan_offset, mm->numa_scan_seq, #endif #if defined(CONFIG_NUMA_BALANCING) || defined(CONFIG_COMPACTION) - mm->tlb_flush_pending, + atomic_read(&mm->tlb_flush_pending), #endif mm->def_flags, &mm->def_flags ); -- 2.11.0 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org