From: Neil Brown <neilb@cse.unsw.edu.au>
Yes.. should only happen if two separate read (or write) requests for the
same sector are concurrent, which I wouldn't have thought would happen, but
maybe tail-packing or similar could cause two independent requests for the
same piece of disc.
This hack/patch might fix it but I'm not in a position to test it.
I'll try to work out a better fix in the next week or two.
Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
25-akpm/drivers/md/raid5.c | 18 ++++++++++++++----
1 files changed, 14 insertions(+), 4 deletions(-)
diff -puN drivers/md/raid5.c~raid5-overlapping-read-hack drivers/md/raid5.c
--- 25/drivers/md/raid5.c~raid5-overlapping-read-hack 2005-01-09 22:20:40.211246912 -0800
+++ 25-akpm/drivers/md/raid5.c 2005-01-09 22:20:40.216246152 -0800
@@ -232,6 +232,7 @@ static struct stripe_head *__find_stripe
}
static void unplug_slaves(mddev_t *mddev);
+static void raid5_unplug_device(request_queue_t *q);
static struct stripe_head *get_active_stripe(raid5_conf_t *conf, sector_t sector,
int pd_idx, int noblock)
@@ -793,7 +794,7 @@ static void compute_parity(struct stripe
* toread/towrite point to the first in a chain.
* The bi_next chain must be in order.
*/
-static void add_stripe_bio (struct stripe_head *sh, struct bio *bi, int dd_idx, int forwrite)
+static int add_stripe_bio (struct stripe_head *sh, struct bio *bi, int dd_idx, int forwrite)
{
struct bio **bip;
raid5_conf_t *conf = sh->raid_conf;
@@ -810,10 +811,10 @@ static void add_stripe_bio (struct strip
else
bip = &sh->dev[dd_idx].toread;
while (*bip && (*bip)->bi_sector < bi->bi_sector) {
- BUG_ON((*bip)->bi_sector + ((*bip)->bi_size >> 9) > bi->bi_sector);
+ if ((*bip)->bi_sector + ((*bip)->bi_size >> 9) > bi->bi_sector)
+ return 0; /* cannot add just now due to overlap */
bip = & (*bip)->bi_next;
}
-/* FIXME do I need to worry about overlapping bion */
if (*bip && bi->bi_next && (*bip) != bi->bi_next)
BUG();
if (*bip)
@@ -840,6 +841,7 @@ static void add_stripe_bio (struct strip
if (sector >= sh->dev[dd_idx].sector + STRIPE_SECTORS)
set_bit(R5_OVERWRITE, &sh->dev[dd_idx].flags);
}
+ return 1;
}
@@ -1413,7 +1415,15 @@ static int make_request (request_queue_t
sh = get_active_stripe(conf, new_sector, pd_idx, (bi->bi_rw&RWA_MASK));
if (sh) {
- add_stripe_bio(sh, bi, dd_idx, (bi->bi_rw&RW_MASK));
+ while (!add_stripe_bio(sh, bi, dd_idx, (bi->bi_rw&RW_MASK))) {
+ /* add failed due to overlap. Flush everything
+ * and wait a while
+ * FIXME - overlapping requests should be handled better
+ */
+ raid5_unplug_device(mddev->queue);
+ set_current_state(TASK_UNINTERRUPTIBLE);
+ schedule_timeout(1);
+ }
raid5_plug_device(conf);
handle_stripe(sh);
_