[PATCHv2] mm/page_owner: use kvmalloc instead of kmalloc

[miles.chen]

From: Miles Chen <miles.chen@xxxxxxxxxxxx>

The kbuf used by page owner is allocated by kmalloc(), which means it
can use only normal memory and there might be a "out of memory"
issue when we're out of normal memory.

Use kvmalloc() so we can also allocate kbuf from
normal/hihghmem on 32bit kernel.

Clamp the kbuf size to PAGE_SIZE.

Change since v1:
  - use kvmalloc()
  - clamp buffer size to PAGE_SIZE

Signed-off-by: Miles Chen <miles.chen@xxxxxxxxxxxx>
Cc: Joe Perches <joe@xxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
---
 mm/page_owner.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/mm/page_owner.c b/mm/page_owner.c
index d80adfe..a064cd0 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -1,7 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <linux/debugfs.h>
 #include <linux/mm.h>
-#include <linux/slab.h>
 #include <linux/uaccess.h>
 #include <linux/bootmem.h>
 #include <linux/stacktrace.h>
@@ -351,7 +350,8 @@ void pagetypeinfo_showmixedcount_print(struct seq_file *m,
 		.skip = 0
 	};
 
-	kbuf = kmalloc(count, GFP_KERNEL);
+	count = count > PAGE_SIZE ? PAGE_SIZE : count;
+	kbuf = kvmalloc(count, GFP_KERNEL);
 	if (!kbuf)
 		return -ENOMEM;
 
@@ -397,11 +397,11 @@ void pagetypeinfo_showmixedcount_print(struct seq_file *m,
 	if (copy_to_user(buf, kbuf, ret))
 		ret = -EFAULT;
 
-	kfree(kbuf);
+	kvfree(kbuf);
 	return ret;
 
 err:
-	kfree(kbuf);
+	kvfree(kbuf);
 	return -ENOMEM;
 }
 
-- 
1.9.1