Re: [PATCH v6 4/4] md: raid456 add nowait support

On 12/25/21 12:28 AM, Vishal Verma wrote:

On 12/24/21 7:14 PM, Song Liu wrote:

quoted

On Tue, Dec 21, 2021 at 12:06 PM Vishal Verma[off-list ref]  wrote:

quoted

Returns EAGAIN in case the raid456 driver would block
waiting for situations like:

   - Reshape operation,
   - Discard operation.

Signed-off-by: Vishal Verma<redacted>

I think we will need the following fix for raid456:

Ack

quoted

============================ 8< ============================

diff --git i/drivers/md/raid5.c w/drivers/md/raid5.c
index 6ab22f29dacd..55d372ce3300 100644
--- i/drivers/md/raid5.c
+++ w/drivers/md/raid5.c

@@ -5717,6 +5717,7 @@ static void make_discard_request(struct mddev

*mddev, struct bio *bi)
                         raid5_release_stripe(sh);
                         /* Bail out if REQ_NOWAIT is set */
                         if (bi->bi_opf & REQ_NOWAIT) {
+                               finish_wait(&conf->wait_for_overlap, &w);
                                 bio_wouldblock_error(bi);
                                 return;
                         }

@@ -5734,6 +5735,7 @@ static void make_discard_request(struct mddev

*mddev, struct bio *bi)
                                 raid5_release_stripe(sh);
                                 /* Bail out if REQ_NOWAIT is set */
                                 if (bi->bi_opf & REQ_NOWAIT) {
+
finish_wait(&conf->wait_for_overlap, &w);
                                         bio_wouldblock_error(bi);
                                         return;
                                 }

@@ -5829,7 +5831,6 @@ static bool raid5_make_request(struct mddev

*mddev, struct bio * bi)
         last_sector = bio_end_sector(bi);
         bi->bi_next = NULL;

-       md_account_bio(mddev, &bi);
         /* Bail out if REQ_NOWAIT is set */
         if ((bi->bi_opf & REQ_NOWAIT) &&
             (conf->reshape_progress != MaxSector) &&

@@ -5837,9 +5838,11 @@ static bool raid5_make_request(struct mddev

*mddev, struct bio * bi)
             ? (logical_sector > conf->reshape_progress &&
logical_sector <= conf->reshape_safe)
             : (logical_sector >= conf->reshape_safe && logical_sector
< conf->reshape_progress))) {
                 bio_wouldblock_error(bi);
+               if (rw == WRITE)
+                       md_write_end(mddev);
                 return true;
         }
-
+       md_account_bio(mddev, &bi);
         prepare_to_wait(&conf->wait_for_overlap, &w, TASK_UNINTERRUPTIBLE);
         for (; logical_sector < last_sector; logical_sector +=
RAID5_STRIPE_SECTORS(conf)) {
                 int previous;

============================ 8< ============================

Vishal, please try to trigger all these conditions (including raid1,
raid10) and make sure
they work properly.

For example, I triggered raid5 reshape and used something like the
following to make
sure the logic is triggered:

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 55d372ce3300..e79de48a0027 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c

@@ -5840,6 +5840,11 @@ static bool raid5_make_request(struct mddev

*mddev, struct bio * bi)
                 bio_wouldblock_error(bi);
                 if (rw == WRITE)
                         md_write_end(mddev);
+               {
+                       static int count = 0;
+                       if (count++ < 10)
+                               pr_info("%s REQ_NOWAIT return\n", __func__);
+               }
                 return true;
         }
         md_account_bio(mddev, &bi);

Thanks,
Song

Sure, will try this and verify for raid1/10.

I am running into an issue during raid10 reshape. I can see the nowait 
code getting triggered during reshape, but it seems like the reshape 
operation was stuck as soon as I issued write IO using FIO to the array 
during reshape.
FIO also seem stuck i.e no IO went through...