[RFC -mm] mm: Fix races between swapoff and flush dcache

From: Huang, Ying
Date: Mon Feb 26 2018 - 19:44:49 EST

From: Huang Ying <ying.huang@xxxxxxxxx>

>From commit 4b3ef9daa4fc ("mm/swap: split swap cache into 64MB
trunks") on, after swapoff, the address_space associated with the swap
device will be freed. So page_mapping() users which may touch the
address_space need some kind of mechanism to prevent the address_space
from being freed during accessing.

The dcache flushing functions (flush_dcache_page(), etc) in
architecture specific code may access the address_space of swap device
for anonymous pages in swap cache via page_mapping() function. But in
some cases there are no mechanisms to prevent the swap device from
being swapoff, for example,

CPU1 CPU2
__get_user_pages() swapoff()
flush_dcache_page()
mapping = page_mapping()
... exit_swap_address_space()
... kvfree(spaces)
mapping_mapped(mapping)

The address space may be accessed after being freed.

But from cachetlb.txt and Russell King, flush_dcache_page() only care
about file cache pages, for anonymous pages, flush_anon_page() should
be used. The implementation of flush_dcache_page() in all
architectures follows this too. They will check whether
page_mapping() is NULL and whether mapping_mapped() is true to
determine whether to flush the dcache immediately. And they will use
interval tree (mapping->i_mmap) to find all user space mappings.
While mapping_mapped() and mapping->i_mmap isn't used by anonymous
pages in swap cache at all.

So, to fix the race between swapoff and flush dcache, __page_mapping()
is add to return the address_space for file cache pages and NULL
otherwise. All page_mapping() invoking in flush dcache functions are
replaced with __page_mapping().

The patch is only build tested, because I have no machine with
architecture other than x86.

Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Chen Liqin <liqin.linux@xxxxxxxxx>
Cc: Russell King <linux@xxxxxxxxxxxxxxx>
Cc: Yoshinori Sato <ysato@xxxxxxxxxxxxxxxxxxxx>
Cc: "James E.J. Bottomley" <jejb@xxxxxxxxxxxxxxxx>
Cc: Guan Xuetao <gxt@xxxxxxxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Chris Zankel <chris@xxxxxxxxxx>
Cc: Vineet Gupta <vgupta@xxxxxxxxxxxx>
Cc: Ley Foon Tan <lftan@xxxxxxxxxx>
Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
---
arch/arc/mm/cache.c | 2 +-
arch/arm/mm/copypage-v4mc.c | 2 +-
arch/arm/mm/copypage-v6.c | 2 +-
arch/arm/mm/copypage-xscale.c | 2 +-
arch/arm/mm/fault-armv.c | 2 +-
arch/arm/mm/flush.c | 6 +++---
arch/mips/mm/cache.c | 2 +-
arch/nios2/mm/cacheflush.c | 4 ++--
arch/parisc/kernel/cache.c | 4 ++--
arch/score/mm/cache.c | 4 ++--
arch/sh/mm/cache-sh4.c | 2 +-
arch/sh/mm/cache-sh7705.c | 2 +-
arch/sparc/kernel/smp_64.c | 8 ++++----
arch/sparc/mm/init_64.c | 6 +++---
arch/sparc/mm/tlb.c | 2 +-
arch/unicore32/mm/flush.c | 2 +-
arch/unicore32/mm/mmu.c | 2 +-
arch/xtensa/mm/cache.c | 2 +-
include/linux/mm.h | 1 +
mm/util.c | 20 ++++++++++++++++++++
20 files changed, 49 insertions(+), 28 deletions(-)

diff --git a/arch/arc/mm/cache.c b/arch/arc/mm/cache.c
index 2072f3451e9c..0f607d5a85da 100644
--- a/arch/arc/mm/cache.c
+++ b/arch/arc/mm/cache.c
@@ -833,7 +833,7 @@ void flush_dcache_page(struct page *page)
}

/* don't handle anon pages here */
- mapping = page_mapping(page);
+ mapping = __page_mapping(page);
if (!mapping)
return;

diff --git a/arch/arm/mm/copypage-v4mc.c b/arch/arm/mm/copypage-v4mc.c
index 1267e64133b9..6d9e632ca43b 100644
--- a/arch/arm/mm/copypage-v4mc.c
+++ b/arch/arm/mm/copypage-v4mc.c
@@ -70,7 +70,7 @@ void v4_mc_copy_user_highpage(struct page *to, struct page *from,
void *kto = kmap_atomic(to);

if (!test_and_set_bit(PG_dcache_clean, &from->flags))
- __flush_dcache_page(page_mapping(from), from);
+ __flush_dcache_page(__page_mapping(from), from);

raw_spin_lock(&minicache_lock);

diff --git a/arch/arm/mm/copypage-v6.c b/arch/arm/mm/copypage-v6.c
index 70423345da26..2f13ffd847a6 100644
--- a/arch/arm/mm/copypage-v6.c
+++ b/arch/arm/mm/copypage-v6.c
@@ -76,7 +76,7 @@ static void v6_copy_user_highpage_aliasing(struct page *to,
unsigned long kfrom, kto;

if (!test_and_set_bit(PG_dcache_clean, &from->flags))
- __flush_dcache_page(page_mapping(from), from);
+ __flush_dcache_page(__page_mapping(from), from);

/* FIXME: not highmem safe */
discard_old_kernel_data(page_address(to));
diff --git a/arch/arm/mm/copypage-xscale.c b/arch/arm/mm/copypage-xscale.c
index 0fb85025344d..221129649627 100644
--- a/arch/arm/mm/copypage-xscale.c
+++ b/arch/arm/mm/copypage-xscale.c
@@ -90,7 +90,7 @@ void xscale_mc_copy_user_highpage(struct page *to, struct page *from,
void *kto = kmap_atomic(to);

if (!test_and_set_bit(PG_dcache_clean, &from->flags))
- __flush_dcache_page(page_mapping(from), from);
+ __flush_dcache_page(__page_mapping(from), from);

raw_spin_lock(&minicache_lock);

diff --git a/arch/arm/mm/fault-armv.c b/arch/arm/mm/fault-armv.c
index d9e0d00a6699..593bd1549ce0 100644
--- a/arch/arm/mm/fault-armv.c
+++ b/arch/arm/mm/fault-armv.c
@@ -195,7 +195,7 @@ void update_mmu_cache(struct vm_area_struct *vma, unsigned long addr,
if (page == ZERO_PAGE(0))
return;

- mapping = page_mapping(page);
+ mapping = __page_mapping(page);
if (!test_and_set_bit(PG_dcache_clean, &page->flags))
__flush_dcache_page(mapping, page);
if (mapping) {
diff --git a/arch/arm/mm/flush.c b/arch/arm/mm/flush.c
index f1e6190aa7ea..2e4a478c6f02 100644
--- a/arch/arm/mm/flush.c
+++ b/arch/arm/mm/flush.c
@@ -285,7 +285,7 @@ void __sync_icache_dcache(pte_t pteval)

page = pfn_to_page(pfn);
if (cache_is_vipt_aliasing())
- mapping = page_mapping(page);
+ mapping = __page_mapping(page);
else
mapping = NULL;

@@ -333,7 +333,7 @@ void flush_dcache_page(struct page *page)
return;
}

- mapping = page_mapping(page);
+ mapping = __page_mapping(page);

if (!cache_ops_need_broadcast() &&
mapping && !page_mapcount(page))
@@ -363,7 +363,7 @@ void flush_kernel_dcache_page(struct page *page)
if (cache_is_vivt() || cache_is_vipt_aliasing()) {
struct address_space *mapping;

- mapping = page_mapping(page);
+ mapping = __page_mapping(page);

if (!mapping || mapping_mapped(mapping)) {
void *addr;
diff --git a/arch/mips/mm/cache.c b/arch/mips/mm/cache.c
index 44ac64d51827..8a21c0345516 100644
--- a/arch/mips/mm/cache.c
+++ b/arch/mips/mm/cache.c
@@ -86,7 +86,7 @@ SYSCALL_DEFINE3(cacheflush, unsigned long, addr, unsigned long, bytes,

void __flush_dcache_page(struct page *page)
{
- struct address_space *mapping = page_mapping(page);
+ struct address_space *mapping = __page_mapping(page);
unsigned long addr;

if (mapping && !mapping_mapped(mapping)) {
diff --git a/arch/nios2/mm/cacheflush.c b/arch/nios2/mm/cacheflush.c
index 87bf88ed04c6..117bece3eb80 100644
--- a/arch/nios2/mm/cacheflush.c
+++ b/arch/nios2/mm/cacheflush.c
@@ -180,7 +180,7 @@ void flush_dcache_page(struct page *page)
if (page == ZERO_PAGE(0))
return;

- mapping = page_mapping(page);
+ mapping = __page_mapping(page);

/* Flush this page if there are aliases. */
if (mapping && !mapping_mapped(mapping)) {
@@ -215,7 +215,7 @@ void update_mmu_cache(struct vm_area_struct *vma,
if (page == ZERO_PAGE(0))
return;

- mapping = page_mapping(page);
+ mapping = __page_mapping(page);
if (!test_and_set_bit(PG_dcache_clean, &page->flags))
__flush_dcache_page(mapping, page);

diff --git a/arch/parisc/kernel/cache.c b/arch/parisc/kernel/cache.c
index 7c1bde80ada4..2150dd193654 100644
--- a/arch/parisc/kernel/cache.c
+++ b/arch/parisc/kernel/cache.c
@@ -88,7 +88,7 @@ update_mmu_cache(struct vm_area_struct *vma, unsigned long address, pte_t *ptep)
return;

page = pfn_to_page(pfn);
- if (page_mapping(page) && test_bit(PG_dcache_dirty, &page->flags)) {
+ if (__page_mapping(page) && test_bit(PG_dcache_dirty, &page->flags)) {
flush_kernel_dcache_page_addr(pfn_va(pfn));
clear_bit(PG_dcache_dirty, &page->flags);
} else if (parisc_requires_coherency())
@@ -304,7 +304,7 @@ __flush_cache_page(struct vm_area_struct *vma, unsigned long vmaddr,

void flush_dcache_page(struct page *page)
{
- struct address_space *mapping = page_mapping(page);
+ struct address_space *mapping = __page_mapping(page);
struct vm_area_struct *mpnt;
unsigned long offset;
unsigned long addr, old_addr = 0;
diff --git a/arch/score/mm/cache.c b/arch/score/mm/cache.c
index b4bcfd3e8393..a74967a396e6 100644
--- a/arch/score/mm/cache.c
+++ b/arch/score/mm/cache.c
@@ -54,7 +54,7 @@ static void flush_data_cache_page(unsigned long addr)

void flush_dcache_page(struct page *page)
{
- struct address_space *mapping = page_mapping(page);
+ struct address_space *mapping = __page_mapping(page);
unsigned long addr;

if (PageHighMem(page))
@@ -86,7 +86,7 @@ void __update_cache(struct vm_area_struct *vma, unsigned long address,
if (unlikely(!pfn_valid(pfn)))
return;
page = pfn_to_page(pfn);
- if (page_mapping(page) && test_bit(PG_dcache_dirty, &(page)->flags)) {
+ if (__page_mapping(page) && test_bit(PG_dcache_dirty, &(page)->flags)) {
addr = (unsigned long) page_address(page);
if (exec)
flush_data_cache_page(addr);
diff --git a/arch/sh/mm/cache-sh4.c b/arch/sh/mm/cache-sh4.c
index 58aaa4f33b81..281e33daaa98 100644
--- a/arch/sh/mm/cache-sh4.c
+++ b/arch/sh/mm/cache-sh4.c
@@ -112,7 +112,7 @@ static void sh4_flush_dcache_page(void *arg)
struct page *page = arg;
unsigned long addr = (unsigned long)page_address(page);
#ifndef CONFIG_SMP
- struct address_space *mapping = page_mapping(page);
+ struct address_space *mapping = __page_mapping(page);

if (mapping && !mapping_mapped(mapping))
clear_bit(PG_dcache_clean, &page->flags);
diff --git a/arch/sh/mm/cache-sh7705.c b/arch/sh/mm/cache-sh7705.c
index 6cd2aa395817..92db57ccc35a 100644
--- a/arch/sh/mm/cache-sh7705.c
+++ b/arch/sh/mm/cache-sh7705.c
@@ -136,7 +136,7 @@ static void __flush_dcache_page(unsigned long phys)
static void sh7705_flush_dcache_page(void *arg)
{
struct page *page = arg;
- struct address_space *mapping = page_mapping(page);
+ struct address_space *mapping = __page_mapping(page);

if (mapping && !mapping_mapped(mapping))
clear_bit(PG_dcache_clean, &page->flags);
diff --git a/arch/sparc/kernel/smp_64.c b/arch/sparc/kernel/smp_64.c
index c50182cd2f64..5bd8b67e66f2 100644
--- a/arch/sparc/kernel/smp_64.c
+++ b/arch/sparc/kernel/smp_64.c
@@ -929,9 +929,9 @@ static inline void __local_flush_dcache_page(struct page *page)
#ifdef DCACHE_ALIASING_POSSIBLE
__flush_dcache_page(page_address(page),
((tlb_type == spitfire) &&
- page_mapping(page) != NULL));
+ __page_mapping(page) != NULL));
#else
- if (page_mapping(page) != NULL &&
+ if (__page_mapping(page) != NULL &&
tlb_type == spitfire)
__flush_icache_page(__pa(page_address(page)));
#endif
@@ -958,7 +958,7 @@ void smp_flush_dcache_page_impl(struct page *page, int cpu)

if (tlb_type == spitfire) {
data0 = ((u64)&xcall_flush_dcache_page_spitfire);
- if (page_mapping(page) != NULL)
+ if (__page_mapping(page) != NULL)
data0 |= ((u64)1 << 32);
} else if (tlb_type == cheetah || tlb_type == cheetah_plus) {
#ifdef DCACHE_ALIASING_POSSIBLE
@@ -994,7 +994,7 @@ void flush_dcache_page_all(struct mm_struct *mm, struct page *page)
pg_addr = page_address(page);
if (tlb_type == spitfire) {
data0 = ((u64)&xcall_flush_dcache_page_spitfire);
- if (page_mapping(page) != NULL)
+ if (__page_mapping(page) != NULL)
data0 |= ((u64)1 << 32);
} else if (tlb_type == cheetah || tlb_type == cheetah_plus) {
#ifdef DCACHE_ALIASING_POSSIBLE
diff --git a/arch/sparc/mm/init_64.c b/arch/sparc/mm/init_64.c
index a9f94e911e0a..6f0f3f2b04a9 100644
--- a/arch/sparc/mm/init_64.c
+++ b/arch/sparc/mm/init_64.c
@@ -206,9 +206,9 @@ inline void flush_dcache_page_impl(struct page *page)
#ifdef DCACHE_ALIASING_POSSIBLE
__flush_dcache_page(page_address(page),
((tlb_type == spitfire) &&
- page_mapping(page) != NULL));
+ __page_mapping(page) != NULL));
#else
- if (page_mapping(page) != NULL &&
+ if (__page_mapping(page) != NULL &&
tlb_type == spitfire)
__flush_icache_page(__pa(page_address(page)));
#endif
@@ -490,7 +490,7 @@ void flush_dcache_page(struct page *page)

this_cpu = get_cpu();

- mapping = page_mapping(page);
+ mapping = __page_mapping(page);
if (mapping && !mapping_mapped(mapping)) {
int dirty = test_bit(PG_dcache_dirty, &page->flags);
if (dirty) {
diff --git a/arch/sparc/mm/tlb.c b/arch/sparc/mm/tlb.c
index 847ddffbf38a..5d7c13b88a42 100644
--- a/arch/sparc/mm/tlb.c
+++ b/arch/sparc/mm/tlb.c
@@ -128,7 +128,7 @@ void tlb_batch_add(struct mm_struct *mm, unsigned long vaddr,
goto no_cache_flush;

/* A real file page? */
- mapping = page_mapping(page);
+ mapping = __page_mapping(page);
if (!mapping)
goto no_cache_flush;

diff --git a/arch/unicore32/mm/flush.c b/arch/unicore32/mm/flush.c
index 6d4c096ffa2a..def5142d16ea 100644
--- a/arch/unicore32/mm/flush.c
+++ b/arch/unicore32/mm/flush.c
@@ -83,7 +83,7 @@ void flush_dcache_page(struct page *page)
if (page == ZERO_PAGE(0))
return;

- mapping = page_mapping(page);
+ mapping = __page_mapping(page);

if (mapping && !mapping_mapped(mapping))
clear_bit(PG_dcache_clean, &page->flags);
diff --git a/arch/unicore32/mm/mmu.c b/arch/unicore32/mm/mmu.c
index 4f5a532bee13..2bd143b7aca3 100644
--- a/arch/unicore32/mm/mmu.c
+++ b/arch/unicore32/mm/mmu.c
@@ -503,7 +503,7 @@ void update_mmu_cache(struct vm_area_struct *vma, unsigned long addr,
if (page == ZERO_PAGE(0))
return;

- mapping = page_mapping(page);
+ mapping = __page_mapping(page);
if (!test_and_set_bit(PG_dcache_clean, &page->flags))
__flush_dcache_page(mapping, page);
if (mapping)
diff --git a/arch/xtensa/mm/cache.c b/arch/xtensa/mm/cache.c
index 57dc231a0709..17485819d03b 100644
--- a/arch/xtensa/mm/cache.c
+++ b/arch/xtensa/mm/cache.c
@@ -127,7 +127,7 @@ EXPORT_SYMBOL(copy_user_highpage);

void flush_dcache_page(struct page *page)
{
- struct address_space *mapping = page_mapping(page);
+ struct address_space *mapping = __page_mapping(page);

/*
* If we have a mapping but the page is not mapped to user-space
diff --git a/include/linux/mm.h b/include/linux/mm.h
index c500bdfadf79..16d5e27b4438 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1146,6 +1146,7 @@ static inline pgoff_t page_index(struct page *page)
}

bool page_mapped(struct page *page);
+struct address_space *__page_mapping(struct page *page);
struct address_space *page_mapping(struct page *page);

/*
diff --git a/mm/util.c b/mm/util.c
index d800ce40816c..f47f3a1cc3f2 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -490,6 +490,26 @@ struct anon_vma *page_anon_vma(struct page *page)
return __page_rmapping(page);
}

+/*
+ * For file cache pages, return the address_space, otherwise return NULL
+ */
+struct address_space *__page_mapping(struct page *page)
+{
+ struct address_space *mapping;
+
+ page = compound_head(page);
+
+ /* This happens if someone calls flush_dcache_page on slab page */
+ if (unlikely(PageSlab(page)))
+ return NULL;
+
+ mapping = page->mapping;
+ if ((unsigned long)mapping & PAGE_MAPPING_ANON)
+ return NULL;
+
+ return (void *)((unsigned long)mapping & ~PAGE_MAPPING_FLAGS);
+}
+
struct address_space *page_mapping(struct page *page)
{
struct address_space *mapping;
--
2.15.1