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

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Date:	Wed, 12 Sep 2012 10:43:51 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Minchan Kim <minchan@...nel.org>,
	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Michal Nazarewicz <mina86@...a86.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Wen Congyang <wency@...fujitsu.com>
Subject: [PATCH 2/2] memory-hotplug: don't replace lowmem pages with highmem

[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)
      Backtrace:
      [<c010e3f0>] (ext4_getblk+0x0/0x180) from [<c010e58c>] (ext4_bread+0x1c/0x98)
      [<c010e570>] (ext4_bread+0x0/0x98) from [<c0117944>] (ext4_mkdir+0x160/0x3bc)
       r4:c15337f0
      [<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@...fujitsu.com>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
Cc: Michal Nazarewicz <mina86@...a86.com>
Cc: Marek Szyprowski <m.szyprowski@...sung.com>
Cc: Wen Congyang <wency@...fujitsu.com>
Signed-off-by: Minchan Kim <minchan@...nel.org>
---
 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);
-}
-
 #define NR_OFFLINE_AT_ONCE_PAGES	(256)
 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)
 			putback_lru_pages(&source);
 			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,
 							true, MIGRATE_SYNC);
 		if (ret)
 			putback_lru_pages(&source);
-- 
1.7.9.5

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