[PATCH 2/2] memory-hotplug: don't replace lowmem pages with highmem

From: Minchan Kim
Date: Tue Sep 11 2012 - 21:42:47 EST

[1] reporeted that lowmem pages could be replaced by
highmem pages during migration of CMA and fixed.

Quote from [1]'s description
The filesystem layer expects pages in the block device's mapping to not
be in highmem (the mapping's gfp mask is set in bdget()), but CMA can
currently replace lowmem pages with highmem pages, leading to crashes in
filesystem code such as the one below:

Unable to handle kernel NULL pointer dereference at virtual address 00000400
pgd = c0c98000
[00000400] *pgd=00c91831, *pte=00000000, *ppte=00000000
Internal error: Oops: 817 [#1] PREEMPT SMP ARM
CPU: 0 Not tainted (3.5.0-rc5+ #80)
PC is at __memzero+0x24/0x80
Process fsstress (pid: 323, stack limit = 0xc0cbc2f0)
[<c010e3f0>] (ext4_getblk+0x0/0x180) from [<c010e58c>] (ext4_bread+0x1c/0x98)
[<c010e570>] (ext4_bread+0x0/0x98) from [<c0117944>] (ext4_mkdir+0x160/0x3bc)
[<c01177e4>] (ext4_mkdir+0x0/0x3bc) from [<c00c29e0>] (vfs_mkdir+0x8c/0x98)
[<c00c2954>] (vfs_mkdir+0x0/0x98) from [<c00c2a60>] (sys_mkdirat+0x74/0xac)
r6:00000000 r5:c152eb40 r4:000001ff r3:c14b43f0
[<c00c29ec>] (sys_mkdirat+0x0/0xac) from [<c00c2ab8>] (sys_mkdir+0x20/0x24)
r6:beccdcf0 r5:00074000 r4:beccdbbc
[<c00c2a98>] (sys_mkdir+0x0/0x24) from [<c000e3c0>] (ret_fast_syscall+0x0/0x30)

Memory-hotplug has same problem with CMA so [1]'s fix could be applied
with memory-hotplug, too.

Fix it by reusing.

[1] 6a6dccba2, mm: cma: don't replace lowmem pages with highmem

Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>
Cc: Michal Nazarewicz <mina86@xxxxxxxxxx>
Cc: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>
Cc: Wen Congyang <wency@xxxxxxxxxxxxxx>
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
mm/memory_hotplug.c | 15 ++++++---------
1 file changed, 6 insertions(+), 9 deletions(-)

diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 4491a6b..fb71e5c 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -752,13 +752,6 @@ static unsigned long scan_lru_pages(unsigned long start, unsigned long end)
return 0;

-static struct page *
-hotremove_migrate_alloc(struct page *page, unsigned long private, int **x)
- /* This should be improooooved!! */
- return alloc_page(GFP_HIGHUSER_MOVABLE);
static int
do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
@@ -809,8 +802,12 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn)
goto out;
- /* this function returns # of failed pages */
- ret = migrate_pages(&source, hotremove_migrate_alloc, 0,
+ /*
+ * alloc_migrate_target should be improooooved!!
+ * migrate_pages returns # of failed pages.
+ */
+ ret = migrate_pages(&source, alloc_migrate_target, 0,
if (ret)

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