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From: Steven Whitehouse on 15 Jul 2010 10:20
From: Abhijith Das <adas(a)redhat.com>

HighMem pages on i686 do not get mapped to the buffer_heads and this was
causing a NULL pointer dereference when we were trying to memset page buffers
to zero.
We now use zero_user() that kmaps the page and directly manipulates page data.
This patch also fixes a boundary condition that was incorrect.

Signed-off-by: Abhi Das <adas(a)redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho(a)redhat.com>

diff --git a/fs/gfs2/quota.c b/fs/gfs2/quota.c
index 49667d6..b256d6f 100644
--- a/fs/gfs2/quota.c
+++ b/fs/gfs2/quota.c
@@ -694,10 +694,8 @@ get_a_page:
if (!buffer_mapped(bh))
goto unlock_out;
/* If it's a newly allocated disk block for quota, zero it */
- if (buffer_new(bh)) {
- memset(bh->b_data, 0, bh->b_size);
- set_buffer_uptodate(bh);
- }
+ if (buffer_new(bh))
+ zero_user(page, pos - blocksize, bh->b_size);
}

if (PageUptodate(page))
@@ -723,7 +721,7 @@ get_a_page:

/* If quota straddles page boundary, we need to update the rest of the
* quota at the beginning of the next page */
- if (offset != 0) { /* first page, offset is closer to PAGE_CACHE_SIZE */
+ if ((offset + sizeof(struct gfs2_quota)) > PAGE_CACHE_SIZE) {
ptr = ptr + nbytes;
nbytes = sizeof(struct gfs2_quota) - nbytes;
offset = 0;
--
1.7.1.1

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