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Subject[md PATCH 2/6] md: Use REQ_FAILFAST_* on metadata writes where appropriate
This can only be supported on personalities which ensure
that md_error() never causes an array to enter the 'failed'
state. i.e. if marking a device Faulty would cause some
data to be inaccessible, the device is status is left as
non-Faulty. This is true for RAID1 and RAID10.

If we get a failure writing metadata but the device doesn't
fail, it must be the last device so we re-write without
FAILFAST to improve chance of success. We also flag the
device as LastDev so that future metadata updates don't
waste time on failfast writes.

Signed-off-by: NeilBrown <neilb@suse.com>
---
drivers/md/bitmap.c | 15 ++++++++++++---
drivers/md/md.c | 44 ++++++++++++++++++++++++++++++++++----------
drivers/md/md.h | 21 ++++++++++++++++++++-
drivers/md/raid1.c | 1 +
drivers/md/raid10.c | 1 +
5 files changed, 68 insertions(+), 14 deletions(-)

diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index cf77cbf9ed22..c4621571b718 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -209,11 +209,13 @@ static struct md_rdev *next_active_rdev(struct md_rdev *rdev, struct mddev *mdde

static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait)
{
- struct md_rdev *rdev = NULL;
+ struct md_rdev *rdev;
struct block_device *bdev;
struct mddev *mddev = bitmap->mddev;
struct bitmap_storage *store = &bitmap->storage;

+restart:
+ rdev = NULL;
while ((rdev = next_active_rdev(rdev, mddev)) != NULL) {
int size = PAGE_SIZE;
loff_t offset = mddev->bitmap_info.offset;
@@ -269,8 +271,8 @@ static int write_sb_page(struct bitmap *bitmap, struct page *page, int wait)
page);
}

- if (wait)
- md_super_wait(mddev);
+ if (wait && md_super_wait(mddev) < 0)
+ goto restart;
return 0;

bad_alignment:
@@ -428,6 +430,13 @@ static void bitmap_wait_writes(struct bitmap *bitmap)
wait_event(bitmap->write_wait,
atomic_read(&bitmap->pending_writes)==0);
else
+ /* Note that we ignore the return value. The writes
+ * might have failed, but that would just mean that
+ * some bits which should be cleared haven't been,
+ * which is safe. The relevant bitmap blocks will
+ * probably get written again, but there is no great
+ * loss if they aren't.
+ */
md_super_wait(bitmap->mddev);
}

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 0d1a9fd9d1c1..047e7db1381b 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -726,7 +726,13 @@ static void super_written(struct bio *bio)
if (bio->bi_error) {
pr_err("md: super_written gets error=%d\n", bio->bi_error);
md_error(mddev, rdev);
- }
+ if (!test_bit(Faulty, &rdev->flags)
+ && (bio->bi_opf & MD_FAILFAST)) {
+ set_bit(MD_NEED_REWRITE, &mddev->flags);
+ set_bit(LastDev, &rdev->flags);
+ }
+ } else
+ clear_bit(LastDev, &rdev->flags);

if (atomic_dec_and_test(&mddev->pending_writes))
wake_up(&mddev->sb_wait);
@@ -743,7 +749,13 @@ void md_super_write(struct mddev *mddev, struct md_rdev *rdev,
* if zero is reached.
* If an error occurred, call md_error
*/
- struct bio *bio = bio_alloc_mddev(GFP_NOIO, 1, mddev);
+ struct bio *bio;
+ int ff = 0;
+
+ if (test_bit(Faulty, &rdev->flags))
+ return;
+
+ bio = bio_alloc_mddev(GFP_NOIO, 1, mddev);

atomic_inc(&rdev->nr_pending);

@@ -752,16 +764,24 @@ void md_super_write(struct mddev *mddev, struct md_rdev *rdev,
bio_add_page(bio, page, size, 0);
bio->bi_private = rdev;
bio->bi_end_io = super_written;
- bio_set_op_attrs(bio, REQ_OP_WRITE, WRITE_FLUSH_FUA);
+
+ if (test_bit(MD_FAILFAST_SUPPORTED, &mddev->flags) &&
+ test_bit(FailFast, &rdev->flags) &&
+ !test_bit(LastDev, &rdev->flags))
+ ff = MD_FAILFAST;
+ bio_set_op_attrs(bio, REQ_OP_WRITE, WRITE_FLUSH_FUA | ff);

atomic_inc(&mddev->pending_writes);
submit_bio(bio);
}

-void md_super_wait(struct mddev *mddev)
+int md_super_wait(struct mddev *mddev)
{
/* wait for all superblock writes that were scheduled to complete */
wait_event(mddev->sb_wait, atomic_read(&mddev->pending_writes)==0);
+ if (test_and_clear_bit(MD_NEED_REWRITE, &mddev->flags))
+ return -EAGAIN;
+ return 0;
}

int sync_page_io(struct md_rdev *rdev, sector_t sector, int size,
@@ -1333,9 +1353,10 @@ super_90_rdev_size_change(struct md_rdev *rdev, sector_t num_sectors)
if (IS_ENABLED(CONFIG_LBDAF) && (u64)num_sectors >= (2ULL << 32) &&
rdev->mddev->level >= 1)
num_sectors = (sector_t)(2ULL << 32) - 2;
- md_super_write(rdev->mddev, rdev, rdev->sb_start, rdev->sb_size,
+ do
+ md_super_write(rdev->mddev, rdev, rdev->sb_start, rdev->sb_size,
rdev->sb_page);
- md_super_wait(rdev->mddev);
+ while (md_super_wait(rdev->mddev) < 0);
return num_sectors;
}

@@ -1876,9 +1897,10 @@ super_1_rdev_size_change(struct md_rdev *rdev, sector_t num_sectors)
sb->data_size = cpu_to_le64(num_sectors);
sb->super_offset = rdev->sb_start;
sb->sb_csum = calc_sb_1_csum(sb);
- md_super_write(rdev->mddev, rdev, rdev->sb_start, rdev->sb_size,
- rdev->sb_page);
- md_super_wait(rdev->mddev);
+ do
+ md_super_write(rdev->mddev, rdev, rdev->sb_start, rdev->sb_size,
+ rdev->sb_page);
+ while (md_super_wait(rdev->mddev) < 0);
return num_sectors;

}
@@ -2413,6 +2435,7 @@ void md_update_sb(struct mddev *mddev, int force_change)
pr_debug("md: updating %s RAID superblock on device (in sync %d)\n",
mdname(mddev), mddev->in_sync);

+rewrite:
bitmap_update_sb(mddev->bitmap);
rdev_for_each(rdev, mddev) {
char b[BDEVNAME_SIZE];
@@ -2444,7 +2467,8 @@ void md_update_sb(struct mddev *mddev, int force_change)
/* only need to write one superblock... */
break;
}
- md_super_wait(mddev);
+ if (md_super_wait(mddev) < 0)
+ goto rewrite;
/* if there was a failure, MD_CHANGE_DEVS was set, and we re-write super */

if (mddev_is_clustered(mddev) && ret == 0)
diff --git a/drivers/md/md.h b/drivers/md/md.h
index bc6712ef8c81..5c08f84101fa 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -30,6 +30,16 @@
#define MaxSector (~(sector_t)0)

/*
+ * These flags should really be called "NO_RETRY" rather than
+ * "FAILFAST" because they don't make any promise about time lapse,
+ * only about the number of retries, which will be zero.
+ * REQ_FAILFAST_DRIVER is not included because
+ * Commit: 4a27446f3e39 ("[SCSI] modify scsi to handle new fail fast flags.")
+ * seems to suggest that the errors it avoids retrying should usually
+ * be retried.
+ */
+#define MD_FAILFAST (REQ_FAILFAST_DEV | REQ_FAILFAST_TRANSPORT)
+/*
* MD's 'extended' device
*/
struct md_rdev {
@@ -177,6 +187,10 @@ enum flag_bits {
* It is expects that no bad block log
* is present.
*/
+ LastDev, /* Seems to be the last working dev as
+ * it didn't fail, so don't use FailFast
+ * any more for metadata
+ */
};

static inline int is_badblock(struct md_rdev *rdev, sector_t s, int sectors,
@@ -213,6 +227,11 @@ enum mddev_flags {
MD_CLUSTER_RESYNC_LOCKED, /* cluster raid only, which means node
* already took resync lock, need to
* release the lock */
+ MD_FAILFAST_SUPPORTED, /* Using MD_FAILFAST on metadata writes is
+ * supported as calls to md_error() will
+ * never cause the array to become failed.
+ */
+ MD_NEED_REWRITE, /* metadata write needs to be repeated */
};
#define MD_UPDATE_SB_FLAGS (BIT(MD_CHANGE_DEVS) | \
BIT(MD_CHANGE_CLEAN) | \
@@ -628,7 +647,7 @@ extern int mddev_congested(struct mddev *mddev, int bits);
extern void md_flush_request(struct mddev *mddev, struct bio *bio);
extern void md_super_write(struct mddev *mddev, struct md_rdev *rdev,
sector_t sector, int size, struct page *page);
-extern void md_super_wait(struct mddev *mddev);
+extern int md_super_wait(struct mddev *mddev);
extern int sync_page_io(struct md_rdev *rdev, sector_t sector, int size,
struct page *page, int op, int op_flags,
bool metadata_op);
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 96474f0af1b8..cfd73730e6af 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -2989,6 +2989,7 @@ static int raid1_run(struct mddev *mddev)
mddev->thread = conf->thread;
conf->thread = NULL;
mddev->private = conf;
+ set_bit(MD_FAILFAST_SUPPORTED, &mddev->flags);

md_set_array_sectors(mddev, raid1_size(mddev, 0, 0));

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index b53610c59104..763ca45b6b32 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -3728,6 +3728,7 @@ static int raid10_run(struct mddev *mddev)
size = raid10_size(mddev, 0, 0);
md_set_array_sectors(mddev, size);
mddev->resync_max_sectors = size;
+ set_bit(MD_FAILFAST_SUPPORTED, &mddev->flags);

if (mddev->queue) {
int stripe = conf->geo.raid_disks *

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