The patch titled
Subject: mm: prevent racy access to tlb_flush_pending
has been removed from the -mm tree. Its filename was
mm-prevent-racy-access-to-tlb_flush_pending.patch
This patch was dropped because it had testing failures
------------------------------------------------------
From: Nadav Amit <namit@xxxxxxxxxx>
Subject: mm: prevent racy access to tlb_flush_pending
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")
Link: http://lkml.kernel.org/r/20170717180246.62277-1-namit@xxxxxxxxxx
Signed-off-by: Nadav Amit <namit@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/mm_types.h | 8 ++++----
kernel/fork.c | 2 +-
mm/debug.c | 2 +-
3 files changed, 6 insertions(+), 6 deletions(-)
diff -puN include/linux/mm_types.h~mm-prevent-racy-access-to-tlb_flush_pending include/linux/mm_types.h
--- a/include/linux/mm_types.h~mm-prevent-racy-access-to-tlb_flush_pending
+++ a/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
#ifdef CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
/* See flush_tlb_batched_pending() */
@@ -532,11 +532,11 @@ static inline cpumask_t *mm_cpumask(stru
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
@@ -548,7 +548,7 @@ static inline void set_tlb_flush_pending
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 -puN kernel/fork.c~mm-prevent-racy-access-to-tlb_flush_pending kernel/fork.c
--- a/kernel/fork.c~mm-prevent-racy-access-to-tlb_flush_pending
+++ a/kernel/fork.c
@@ -807,7 +807,7 @@ static struct mm_struct *mm_init(struct
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 -puN mm/debug.c~mm-prevent-racy-access-to-tlb_flush_pending mm/debug.c
--- a/mm/debug.c~mm-prevent-racy-access-to-tlb_flush_pending
+++ a/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
);
_
Patches currently in -mm which might be from namit@xxxxxxxxxx are
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