[PATCH][RFC]JBD2: Fix journal checksum kernel oops on NUMA

[Mingming Cao <cmm@us.ibm.com>]

JBD2: Fix NULL pointer bh->b_data on NUMA box with journal checksumming.

Current journal checksumming patch failed fsstress test on NUMA. The 
bh->b_data passed to the crc32_be () function could be NULL pointer, 
which caused kernel oops immediately when running fsstress with -o 
journal_checksum. It is because the page is part of highmem on NUMA box.
We need to kmap the page before access the bh->b_data to calculate
the checksums.
 
Signed-off-by: Mingming Cao <cmm@us.ibm.com>

---
 fs/jbd2/commit.c |   19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

Index: linux-2.6.24-rc1/fs/jbd2/commit.c
===================================================================
--- linux-2.6.24-rc1.orig/fs/jbd2/commit.c	2007-11-01 11:15:08.000000000 -0700
+++ linux-2.6.24-rc1/fs/jbd2/commit.c	2007-11-01 12:27:02.000000000 -0700
@@ -352,6 +352,20 @@ write_out_data:
 	journal_do_submit_data(wbuf, bufs);
 }
 
+static inline __u32 jbd2_checksum_data(__u32 crc32_sum, struct buffer_head *bh)
+{
+	struct page *page = bh->b_page;
+	char *addr;
+	__u32 checksum;
+
+	addr = kmap(page);
+	checksum = crc32_be(crc32_sum,
+		(void *)(addr + offset_in_page(bh->b_data)), bh->b_size);
+	kunmap(page);
+
+	return checksum;
+}
+
 static inline void write_tag_block(int tag_bytes, journal_block_tag_t *tag,
 				   unsigned long long block)
 {
@@ -715,9 +729,8 @@ start_journal_io:
 				 */
 				if (JBD2_HAS_COMPAT_FEATURE(journal,
 					JBD2_FEATURE_COMPAT_CHECKSUM)) {
-					crc32_sum = crc32_be(crc32_sum,
-							(void *)bh->b_data,
-							bh->b_size);
+					crc32_sum =
+					    jbd2_checksum_data(crc32_sum, bh);
 				}
 
 				lock_buffer(bh);