On Wednesday March 16, lmb@xxxxxxx wrote:
> Mark found a bug where md doesn't handle write failures when trying to
> update the superblock.
>
> Attached is the fix he sent to us, and which seems to apply fine to
> 2.6.11 too.
Yes... thanks....
The whole '100 times' thing is completely bogus isn't it...
By co-incidence, I've just recently be modifying this code to do
writes more intelligently. My goal was to get it to write all the
superblocks in parallel rather than in series. The result is below
which will probably go to Andrew shortly. It add the required
md_error and removes the 'try 100 times'.
It also loops 'round to re-write the superblock if one of the writes
failed, thus dirtying the superblock.
NeilBrown
========================================
Allow md to update multiple superblocks in parallel.
currently, md updates all superblocks (one on each device)
in series. It waits for one write to complete before starting
the next. This isn't a big problem as superblock updates don't
happen that often.
However it is neater to do it in parallel, and if the drives
in the array have gone to "sleep" after a period of idleness, then
waking them is parallel is faster (and someone else should be
worrying about power drain).
Futher, we will need parallel superblock updates for a future
patch which keeps the intent-logging bitmap near the superblock.
Also remove the silly code that retired superblock updates
100 times. This simply never made sense.
Signed-off-by: Neil Brown <neilb@xxxxxxxxxxxxxxx>
### Diffstat output
./drivers/md/md.c | 83 ++++++++++++++++++++++++--------------------
./include/linux/raid/md_k.h | 1
2 files changed, 48 insertions(+), 36 deletions(-)
diff ./drivers/md/md.c~current~ ./drivers/md/md.c
--- ./drivers/md/md.c~current~ 2005-03-14 11:51:29.000000000 +1100
+++ ./drivers/md/md.c 2005-03-15 10:50:13.000000000 +1100
@@ -328,6 +328,40 @@ static void free_disk_sb(mdk_rdev_t * rd
}
+static int super_written(struct bio *bio, unsigned int bytes_done, int error)
+{
+ mdk_rdev_t *rdev = bio->bi_private;
+ if (bio->bi_size)
+ return 1;
+
+ if (error || !test_bit(BIO_UPTODATE, &bio->bi_flags))
+ md_error(rdev->mddev, rdev);
+
+ if (atomic_dec_and_test(&rdev->mddev->pending_writes))
+ wake_up(&rdev->mddev->sb_wait);
+ return 0;
+}
+
+void md_super_write(mddev_t *mddev, mdk_rdev_t *rdev,
+ sector_t sector, int size, struct page *page)
+{
+ /* write first size bytes of page to sector of rdev
+ * Increment mddev->pending_writes before returning
+ * and decrement it on completion, waking up sb_wait
+ * if zero is reached.
+ * If an error occurred, call md_error
+ */
+ struct bio *bio = bio_alloc(GFP_KERNEL, 1);
+
+ bio->bi_bdev = rdev->bdev;
+ bio->bi_sector = sector;
+ bio_add_page(bio, page, size, 0);
+ bio->bi_private = rdev;
+ bio->bi_end_io = super_written;
+ atomic_inc(&mddev->pending_writes);
+ submit_bio((1<<BIO_RW)|(1<<BIO_RW_SYNC), bio);
+}
+
static int bi_complete(struct bio *bio, unsigned int bytes_done, int error)
{
if (bio->bi_size)
@@ -1240,30 +1274,6 @@ void md_print_devices(void)
}
-static int write_disk_sb(mdk_rdev_t * rdev)
-{
- char b[BDEVNAME_SIZE];
- if (!rdev->sb_loaded) {
- MD_BUG();
- return 1;
- }
- if (rdev->faulty) {
- MD_BUG();
- return 1;
- }
-
- dprintk(KERN_INFO "(write) %s's sb offset: %llu\n",
- bdevname(rdev->bdev,b),
- (unsigned long long)rdev->sb_offset);
-
- if (sync_page_io(rdev->bdev, rdev->sb_offset<<1, MD_SB_BYTES, rdev->sb_page, WRITE))
- return 0;
-
- printk("md: write_disk_sb failed for device %s\n",
- bdevname(rdev->bdev,b));
- return 1;
-}
-
static void sync_sbs(mddev_t * mddev)
{
mdk_rdev_t *rdev;
@@ -1278,7 +1288,7 @@ static void sync_sbs(mddev_t * mddev)
static void md_update_sb(mddev_t * mddev)
{
- int err, count = 100;
+ int err;
struct list_head *tmp;
mdk_rdev_t *rdev;
int sync_req;
@@ -1298,6 +1308,7 @@ repeat:
MD_BUG();
mddev->events --;
}
+ mddev->sb_dirty = 2;
sync_sbs(mddev);
/*
@@ -1325,24 +1336,24 @@ repeat:
dprintk("%s ", bdevname(rdev->bdev,b));
if (!rdev->faulty) {
- err += write_disk_sb(rdev);
+ md_super_write(mddev,rdev,
+ rdev->sb_offset<<1, MD_SB_BYTES,
+ rdev->sb_page);
+ dprintk(KERN_INFO "(write) %s's sb offset: %llu\n",
+ bdevname(rdev->bdev,b),
+ (unsigned long long)rdev->sb_offset);
+
} else
dprintk(")\n");
if (!err && mddev->level == LEVEL_MULTIPATH)
/* only need to write one superblock... */
break;
}
- if (err) {
- if (--count) {
- printk(KERN_ERR "md: errors occurred during superblock"
- " update, repeating\n");
- goto repeat;
- }
- printk(KERN_ERR \
- "md: excessive errors occurred during superblock update, exiting\n");
- }
+ wait_event(mddev->sb_wait, atomic_read(&mddev->pending_writes)==0);
+ /* if there was a failure, sb_dirty was set to 1, and we re-write super */
+
spin_lock(&mddev->write_lock);
- if (mddev->in_sync != sync_req) {
+ if (mddev->in_sync != sync_req|| mddev->sb_dirty == 1) {
/* have to write it out again */
spin_unlock(&mddev->write_lock);
goto repeat;
diff ./include/linux/raid/md_k.h~current~ ./include/linux/raid/md_k.h
--- ./include/linux/raid/md_k.h~current~ 2005-03-15 10:26:24.000000000 +1100
+++ ./include/linux/raid/md_k.h 2005-03-15 10:49:06.000000000 +1100
@@ -262,6 +262,7 @@ struct mddev_s
spinlock_t write_lock;
wait_queue_head_t sb_wait; /* for waiting on superblock updates */
+ atomic_t pending_writes; /* number of active superblock writes */
unsigned int safemode; /* if set, update "clean" superblock
* when no writes pending.
-
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