[PATCH] prevent AoE causing cache aliases

[phorton@bitbox.co.uk (Peter Horton)]

This patch prevents the AoE block driver from creating cache aliases of
page cache pages on machines with virtually indexed caches.

Building kernels on an AT91SAM9G20 board without this patch fails with
segmentation faults after a couple of passes.

Signed-off-by: Peter Horton <zero@colonel-panic.org>

Index: linux-2.6.31/drivers/block/aoe/aoecmd.c
===================================================================
--- linux-2.6.31.orig/drivers/block/aoe/aoecmd.c	2009-09-09 23:13:59.000000000 +0100
+++ linux-2.6.31/drivers/block/aoe/aoecmd.c	2009-10-22 10:24:50.000000000 +0100
@@ -735,6 +735,21 @@
 	part_stat_unlock();
 }
 
+/*
+ * Ensure we don't create aliases in VI caches
+ */
+static inline void
+killalias(struct bio *bio)
+{
+	struct bio_vec *bv;
+	int i;
+
+	if (bio_data_dir(bio) == READ)
+		__bio_for_each_segment(bv, bio, i, 0) {
+			flush_dcache_page(bv->bv_page);
+		}
+}
+
 void
 aoecmd_ata_rsp(struct sk_buff *skb)
 {
@@ -853,8 +868,12 @@
 
 	if (buf && --buf->nframesout == 0 && buf->resid == 0) {
 		diskstats(d->gd, buf->bio, jiffies - buf->stime, buf->sector);
-		n = (buf->flags & BUFFL_FAIL) ? -EIO : 0;
-		bio_endio(buf->bio, n);
+		if (buf->flags & BUFFL_FAIL)
+			bio_endio(buf->bio, -EIO);
+		else {
+			killalias(buf->bio);
+			bio_endio(buf->bio, 0);
+		}
 		mempool_free(buf, d->bufpool);
 	}