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authorNeilBrown <neilb@suse.de>2010-03-31 11:21:44 +1100
committerNeilBrown <neilb@suse.de>2010-05-18 15:27:57 +1000
commite555190d82c0f58e825e3cbd9e6ebe2e7ac713bd (patch)
treeea9c8e548c4d5eb5fc903bab05af3bda4192ed00 /drivers/md
parentd754c5ae1ff76b20d3ecde8ad666d7865eada8ae (diff)
md/raid1: delay reads that could overtake behind-writes.
When a raid1 array is configured to support write-behind on some devices, it normally only reads from other devices. If all devices are write-behind (because the rest have failed) it is possible for a read request to be serviced before a behind-write request, which would appear as data corruption. So when forced to read from a WriteMostly device, wait for any write-behind to complete, and don't start any more behind-writes. Signed-off-by: NeilBrown <neilb@suse.de>
Diffstat (limited to 'drivers/md')
-rw-r--r--drivers/md/bitmap.c4
-rw-r--r--drivers/md/bitmap.h1
-rw-r--r--drivers/md/raid1.c25
3 files changed, 22 insertions, 8 deletions
diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index 49d6080387c8..c9c6a345e17b 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -1356,7 +1356,8 @@ void bitmap_endwrite(struct bitmap *bitmap, sector_t offset, unsigned long secto
{
if (!bitmap) return;
if (behind) {
- atomic_dec(&bitmap->behind_writes);
+ if (atomic_dec_and_test(&bitmap->behind_writes))
+ wake_up(&bitmap->behind_wait);
PRINTK(KERN_DEBUG "dec write-behind count %d/%d\n",
atomic_read(&bitmap->behind_writes), bitmap->max_write_behind);
}
@@ -1680,6 +1681,7 @@ int bitmap_create(mddev_t *mddev)
atomic_set(&bitmap->pending_writes, 0);
init_waitqueue_head(&bitmap->write_wait);
init_waitqueue_head(&bitmap->overflow_wait);
+ init_waitqueue_head(&bitmap->behind_wait);
bitmap->mddev = mddev;
diff --git a/drivers/md/bitmap.h b/drivers/md/bitmap.h
index aa82b7caa85f..3797dea4723a 100644
--- a/drivers/md/bitmap.h
+++ b/drivers/md/bitmap.h
@@ -240,6 +240,7 @@ struct bitmap {
atomic_t pending_writes; /* pending writes to the bitmap file */
wait_queue_head_t write_wait;
wait_queue_head_t overflow_wait;
+ wait_queue_head_t behind_wait;
struct sysfs_dirent *sysfs_can_clear;
};
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 2e08e48b02d9..cb2da87ad593 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -857,6 +857,15 @@ static int make_request(mddev_t *mddev, struct bio * bio)
}
mirror = conf->mirrors + rdisk;
+ if (test_bit(WriteMostly, &mirror->rdev->flags) &&
+ bitmap) {
+ /* Reading from a write-mostly device must
+ * take care not to over-take any writes
+ * that are 'behind'
+ */
+ wait_event(bitmap->behind_wait,
+ atomic_read(&bitmap->behind_writes) == 0);
+ }
r1_bio->read_disk = rdisk;
read_bio = bio_clone(bio, GFP_NOIO);
@@ -934,10 +943,14 @@ static int make_request(mddev_t *mddev, struct bio * bio)
set_bit(R1BIO_Degraded, &r1_bio->state);
}
- /* do behind I/O ? */
+ /* do behind I/O ?
+ * Not if there are too many, or cannot allocate memory,
+ * or a reader on WriteMostly is waiting for behind writes
+ * to flush */
if (bitmap &&
(atomic_read(&bitmap->behind_writes)
< mddev->bitmap_info.max_write_behind) &&
+ !waitqueue_active(&bitmap->behind_wait) &&
(behind_pages = alloc_behind_pages(bio)) != NULL)
set_bit(R1BIO_BehindIO, &r1_bio->state);
@@ -2144,15 +2157,13 @@ static int stop(mddev_t *mddev)
{
conf_t *conf = mddev->private;
struct bitmap *bitmap = mddev->bitmap;
- int behind_wait = 0;
/* wait for behind writes to complete */
- while (bitmap && atomic_read(&bitmap->behind_writes) > 0) {
- behind_wait++;
- printk(KERN_INFO "raid1: behind writes in progress on device %s, waiting to stop (%d)\n", mdname(mddev), behind_wait);
- set_current_state(TASK_UNINTERRUPTIBLE);
- schedule_timeout(HZ); /* wait a second */
+ if (bitmap && atomic_read(&bitmap->behind_writes) > 0) {
+ printk(KERN_INFO "raid1: behind writes in progress on device %s, waiting to stop.\n", mdname(mddev));
/* need to kick something here to make sure I/O goes? */
+ wait_event(bitmap->behind_wait,
+ atomic_read(&bitmap->behind_writes) == 0);
}
raise_barrier(conf);