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Subject[RFC PATCH 1/4] mm: introduce a safer interface to check whether a page is managed by SLxB
Date
Several subsystems, including memory-failure, swap, sparse, DRBD etc,
use PageSlab() to check whether a page is managed by SLAB/SLUB/SLOB.
And they treat slab pages differently from pagecache/anonymous pages.

But it's unsafe to use PageSlab() to detect whether a page is managed by
SLUB. SLUB allocates compound pages when page order is bigger than 0 and
only sets PG_slab on head pages. So if a SLUB object is hosted by a tail
page, PageSlab() will incorrectly return false for that object.

Following code from sparse.c triggers this issue, which causes failure
when removing a hot-added memory device.
/*
* Check to see if allocation came from hot-plug-add
*/
if (PageSlab(usemap_page)) {
kfree(usemap);
if (memmap)
__kfree_section_memmap(memmap, PAGES_PER_SECTION);
return;
}
So introduce a transparent huge page and compound page safe macro as below
to check whether a page is managed by SLAB/SLUB/SLOB allocator.

#define page_managed_by_slab(page) (!!PageSlab(compound_trans_head(page)))

Signed-off-by: Jiang Liu <liuj97@gmail.com>
---
arch/arm/mm/init.c | 3 ++-
arch/ia64/kernel/mca_drv.c | 2 +-
arch/unicore32/mm/init.c | 3 ++-
crypto/scatterwalk.c | 2 +-
drivers/ata/libata-sff.c | 3 ++-
drivers/block/drbd/drbd_main.c | 3 ++-
fs/proc/page.c | 4 ++--
include/linux/slab.h | 7 +++++++
mm/memory-failure.c | 6 +++---
mm/sparse.c | 4 +---
10 files changed, 23 insertions(+), 14 deletions(-)
diff --git a/arch/arm/mm/init.c b/arch/arm/mm/init.c
index f54d592..73ff340 100644
--- a/arch/arm/mm/init.c
+++ b/arch/arm/mm/init.c
@@ -18,6 +18,7 @@
#include <linux/initrd.h>
#include <linux/of_fdt.h>
#include <linux/highmem.h>
+#include <linux/huge_mm.h>
#include <linux/gfp.h>
#include <linux/memblock.h>
#include <linux/dma-contiguous.h>
@@ -116,7 +117,7 @@ void show_mem(unsigned int filter)
reserved++;
else if (PageSwapCache(page))
cached++;
- else if (PageSlab(page))
+ else if (page_managed_by_slab(page))
slab++;
else if (!page_count(page))
free++;
diff --git a/arch/ia64/kernel/mca_drv.c b/arch/ia64/kernel/mca_drv.c
index 1c2e894..4415bb6 100644
--- a/arch/ia64/kernel/mca_drv.c
+++ b/arch/ia64/kernel/mca_drv.c
@@ -136,7 +136,7 @@ mca_page_isolate(unsigned long paddr)
return ISOLATE_NG;

/* kick pages having attribute 'SLAB' or 'Reserved' */
- if (PageSlab(p) || PageReserved(p))
+ if (page_managed_by_slab(p) || PageReserved(p))
return ISOLATE_NG;

/* add attribute 'Reserved' and register the page */
diff --git a/arch/unicore32/mm/init.c b/arch/unicore32/mm/init.c
index de186bd..829a0d9 100644
--- a/arch/unicore32/mm/init.c
+++ b/arch/unicore32/mm/init.c
@@ -21,6 +21,7 @@
#include <linux/sort.h>
#include <linux/dma-mapping.h>
#include <linux/export.h>
+#include <linux/huge_mm.h>

#include <asm/sections.h>
#include <asm/setup.h>
@@ -83,7 +84,7 @@ void show_mem(unsigned int filter)
reserved++;
else if (PageSwapCache(page))
cached++;
- else if (PageSlab(page))
+ else if (page_managed_by_slab(page))
slab++;
else if (!page_count(page))
free++;
diff --git a/crypto/scatterwalk.c b/crypto/scatterwalk.c
index 7281b8a..a20e019 100644
--- a/crypto/scatterwalk.c
+++ b/crypto/scatterwalk.c
@@ -54,7 +54,7 @@ static void scatterwalk_pagedone(struct scatter_walk *walk, int out,
struct page *page;

page = sg_page(walk->sg) + ((walk->offset - 1) >> PAGE_SHIFT);
- if (!PageSlab(page))
+ if (!page_managed_by_slab(page))
flush_dcache_page(page);
}

diff --git a/drivers/ata/libata-sff.c b/drivers/ata/libata-sff.c
index d8af325..1ab8378 100644
--- a/drivers/ata/libata-sff.c
+++ b/drivers/ata/libata-sff.c
@@ -38,6 +38,7 @@
#include <linux/module.h>
#include <linux/libata.h>
#include <linux/highmem.h>
+#include <linux/huge_mm.h>

#include "libata.h"

@@ -734,7 +735,7 @@ static void ata_pio_sector(struct ata_queued_cmd *qc)
do_write);
}

- if (!do_write && !PageSlab(page))
+ if (!do_write && !page_managed_by_slab(page))
flush_dcache_page(page);

qc->curbytes += qc->sect_size;
diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
index 920ede2..de5b395 100644
--- a/drivers/block/drbd/drbd_main.c
+++ b/drivers/block/drbd/drbd_main.c
@@ -2734,7 +2734,8 @@ static int _drbd_send_page(struct drbd_conf *mdev, struct page *page,
* put_page(); and would cause either a VM_BUG directly, or
* __page_cache_release a page that would actually still be referenced
* by someone, leading to some obscure delayed Oops somewhere else. */
- if (disable_sendpage || (page_count(page) < 1) || PageSlab(page))
+ if (disable_sendpage || (page_count(page) < 1) ||
+ page_managed_by_slab(page))
return _drbd_no_send_page(mdev, page, offset, size, msg_flags);

msg_flags |= MSG_NOSIGNAL;
diff --git a/fs/proc/page.c b/fs/proc/page.c
index 7fcd0d6..ae42dc7 100644
--- a/fs/proc/page.c
+++ b/fs/proc/page.c
@@ -40,7 +40,7 @@ static ssize_t kpagecount_read(struct file *file, char __user *buf,
ppage = pfn_to_page(pfn);
else
ppage = NULL;
- if (!ppage || PageSlab(ppage))
+ if (!ppage || page_managed_by_slab(ppage))
pcount = 0;
else
pcount = page_mapcount(ppage);
@@ -98,7 +98,7 @@ u64 stable_page_flags(struct page *page)
* Note that page->_mapcount is overloaded in SLOB/SLUB/SLQB, so the
* simple test in page_mapped() is not enough.
*/
- if (!PageSlab(page) && page_mapped(page))
+ if (!page_managed_by_slab(page) && page_mapped(page))
u |= 1 << KPF_MMAP;
if (PageAnon(page))
u |= 1 << KPF_ANON;
diff --git a/include/linux/slab.h b/include/linux/slab.h
index 67d5d94..bb26fab 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -364,4 +364,11 @@ static inline void *kzalloc_node(size_t size, gfp_t flags, int node)

void __init kmem_cache_init_late(void);

+/*
+ * Check whether a page is allocated/managed by SLAB/SLUB/SLOB allocator.
+ * Defined as macro instead of function to avoid header file pollution.
+ */
+#define page_managed_by_slab(page) (!!PageSlab(compound_trans_head(page)))
+#define mem_managed_by_slab(addr) page_managed_by_slab(virt_to_page(addr))
+
#endif /* _LINUX_SLAB_H */
diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index ab1e714..684e7f7 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c
@@ -88,7 +88,7 @@ static int hwpoison_filter_dev(struct page *p)
/*
* page_mapping() does not accept slab pages.
*/
- if (PageSlab(p))
+ if (page_managed_by_slab(p))
return -EINVAL;

mapping = page_mapping(p);
@@ -233,7 +233,7 @@ static int kill_proc(struct task_struct *t, unsigned long addr, int trapno,
*/
void shake_page(struct page *p, int access)
{
- if (!PageSlab(p)) {
+ if (!page_managed_by_slab(p)) {
lru_add_drain_all();
if (PageLRU(p))
return;
@@ -862,7 +862,7 @@ static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
struct page *hpage = compound_head(p);
struct page *ppage;

- if (PageReserved(p) || PageSlab(p))
+ if (PageReserved(p) || page_managed_by_slab(p))
return SWAP_SUCCESS;

/*
diff --git a/mm/sparse.c b/mm/sparse.c
index 6a4bf91..32a908b 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -688,17 +688,15 @@ static void free_map_bootmem(struct page *page, unsigned long nr_pages)

static void free_section_usemap(struct page *memmap, unsigned long *usemap)
{
- struct page *usemap_page;
unsigned long nr_pages;

if (!usemap)
return;

- usemap_page = virt_to_page(usemap);
/*
* Check to see if allocation came from hot-plug-add
*/
- if (PageSlab(usemap_page)) {
+ if (mem_managed_by_slab(usemap)) {
kfree(usemap);
if (memmap)
__kfree_section_memmap(memmap, PAGES_PER_SECTION);
--
1.7.1



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