2.4.2-ac24 buffer.c oops on highmem

Hi,

We've just seen a buffer.c oops in:

Trace; c013b732 <block_prepare_write+22/70>
Trace; c015dbba <ext2_get_block+a/4e0>
Trace; c012a67e <generic_file_write+3ee/710>
Trace; c015dbba <ext2_get_block+a/4e0>
Trace; c01281c0 <file_read_actor+0/f0>
Trace; c01384a6 <sys_write+96/d0>
Trace; c010910b <system_call+33/38>

__block_prepare_write()'s "out:" error handler tries to do a

			memset(bh->b_data, 0, bh->b_size);

even if the buffer's page has already been kmapped for highmem. Highmem pages will obviously have b_data being NULL. Patch below.

I had a quick look through the rest of buffer.c and apart from the initialisation of bh->b_data in set_bh_page(), there are no other references left to b_data once we fix this.

Cheers,
Stephen

@@ -1629,12 +1629,14 @@
 	return 0;
 out:
 	bh = head;
+	block_start = 0;
 	do {
 		if (buffer_new(bh) && !buffer_uptodate(bh)) {
-			memset(bh->b_data, 0, bh->b_size);
+			memset(kaddr+block_start, 0, bh->b_size);
 			set_bit(BH_Uptodate, &bh->b_state);
 			mark_buffer_dirty(bh);
 		}
+		block_start += bh->b_size;
 		bh = bh->b_this_page;
 	} while (bh != head);
 	return err;