Re: 2.6.25.6 raid5 resync oops

From: Dan Williams
Date: Thu Jul 10 2008 - 00:55:24 EST


On Wed, 2008-07-09 at 18:07 -0700, Neil Brown wrote:
> Dan: I think this is your code. In
> __handle_issuing_new_read_requests5
> the
> } else if ((s->uptodate < disks - 1) &&
> test_bit(R5_Insync, &dev->flags)) {
>
> looks wrong. We at least want a test on s->syncing in there, maybe:
> } else if (((s->uptodate < disks - 1) || s->syncing)
> &&
> test_bit(R5_Insync, &dev->flags)) {
>
> and given that we only compute blocks when a device is failed, (see 15
> lines earlier) I think we probably just want
> } else if (test_bit(R5_Insync, &dev->flags)) {
>
> I notice that is was it in linux-next (though the functions are
> renamed - it is fetch_block5 there).

Yes, I had realized it was obsolete... missed that it was buggy.
>
> I wonder if there is still time for 2.6.26 .. probably not. It'll be
> released immediately after lwn.net release their weekly edition :-)

Here is a patch against latest mainline.

---snip--->
md: ensure all blocks are uptodate or locked when syncing

From: Dan Williams <dan.j.williams@xxxxxxxxx>

Remove the dubious attempt to prefer 'compute' over 'read'. Not only is it
wrong given commit c337869d (md: do not compute parity unless it is on a failed
drive), but it can trigger a BUG_ON in handle_parity_checks5().

Cc: <stable@xxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---

drivers/md/raid5.c | 7 +------
1 files changed, 1 insertions(+), 6 deletions(-)


diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 54c8ee2..3b27df5 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -2017,12 +2017,7 @@ static int __handle_issuing_new_read_requests5(struct stripe_head *sh,
*/
s->uptodate++;
return 0; /* uptodate + compute == disks */
- } else if ((s->uptodate < disks - 1) &&
- test_bit(R5_Insync, &dev->flags)) {
- /* Note: we hold off compute operations while checks are
- * in flight, but we still prefer 'compute' over 'read'
- * hence we only read if (uptodate < * disks-1)
- */
+ } else if (test_bit(R5_Insync, &dev->flags)) {
set_bit(R5_LOCKED, &dev->flags);
set_bit(R5_Wantread, &dev->flags);
if (!test_and_set_bit(STRIPE_OP_IO, &sh->ops.pending))


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