[BUG] Compile failure (gcc 2.96 bug?). 2.5.42 raid0.c

From: Peter Chubb (peter@chubb.wattle.id.au)
Date: Mon Oct 14 2002 - 19:18:14 EST


>>>>> "David" == David Mansfield <lkml@dm.cobite.com> writes:

David> Trying to compile 2.5.42 I encountered the following error,
David> which looks a lot like a GCC bug. I did a 'make mrproper; make
David> oldconfig; make bzImage' and it still failed.

(lots of gcc internal structure dump deleted here)

Yes it's a GCC optimiser bug. I'm surprised I didn't see it: I tried
a whole heap of different compilers on that code, and had problems
only on the earlier similar code in raid0_run().

I didn't try redhat's compilers (I run debian) but didn't expect the
behaviour to be that different.

Anyway, please apply this patch (which also fixes the chunk overlap
problems).

diff -Nur --exclude=SCCS --exclude=BitKeeper --exclude=ChangeSet linux-2.5-import/drivers/md/raid0.c linux-2.5-mdfix/drivers/md/raid0.c
--- linux-2.5-import/drivers/md/raid0.c Mon Oct 14 10:32:35 2002
+++ linux-2.5-mdfix/drivers/md/raid0.c Tue Oct 15 10:03:07 2002
@@ -162,6 +162,29 @@
         return 1;
 }
 
+/**
+ * raid0_mergeable_bvec -- tell bio layer if a two requests can be merged
+ * @q: request queue
+ * @bio: the buffer head that's been built up so far
+ * @biovec: the request that could be merged to it.
+ *
+ * Return 1 if the merge is not permitted (because the
+ * result would cross a chunk boundary), 0 otherwise.
+ */
+static int raid0_mergeable_bvec(request_queue_t *q, struct bio *bio, struct bio_vec *biovec)
+{
+ mddev_t *mddev = q->queuedata;
+ sector_t block;
+ unsigned int chunk_size;
+ unsigned int bio_sz;
+
+ chunk_size = mddev->chunk_size >> 10;
+ block = bio->bi_sector >> 1;
+ bio_sz = (bio->bi_size + biovec->bv_len) >> 10;
+
+ return chunk_size < ((block & (chunk_size - 1)) + bio_sz);
+}
+
 static int raid0_run (mddev_t *mddev)
 {
         unsigned cur=0, i=0, nb_zone;
@@ -233,6 +256,8 @@
                 conf->hash_table[i++].zone1 = conf->strip_zone + cur;
                 size -= (conf->smallest->size - zone0_size);
         }
+ blk_queue_max_sectors(&mddev->queue, mddev->chunk_size >> 9);
+ blk_queue_merge_bvec(&mddev->queue, raid0_mergeable_bvec);
         return 0;
 
 out_free_zone_conf:
@@ -262,13 +287,6 @@
         return 0;
 }
 
-/*
- * FIXME - We assume some things here :
- * - requested buffers NEVER bigger than chunk size,
- * - requested buffers NEVER cross stripes limits.
- * Of course, those facts may not be valid anymore (and surely won't...)
- * Hey guys, there's some work out there ;-)
- */
 static int raid0_make_request (request_queue_t *q, struct bio *bio)
 {
         mddev_t *mddev = q->queuedata;
@@ -286,13 +304,16 @@
         
 
         {
+#if __GNUC__ < 3
+ volatile
+#endif
                 sector_t x = block;
                 sector_div(x, (unsigned long)conf->smallest->size);
                 hash = conf->hash_table + x;
         }
 
- /* Sanity check */
- if (chunk_size < (block & (chunk_size - 1)) + (bio->bi_size >> 10))
+ /* Sanity check -- queue functions should prevent this happening */
+ if (unlikely(chunk_size < (block & (chunk_size - 1)) + (bio->bi_size >> 10)))
                 goto bad_map;
  
         if (!hash)
-
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