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authorNeilBrown <neilb@suse.de>2010-03-31 11:21:44 +1100
committerGreg Kroah-Hartman <gregkh@suse.de>2010-08-13 13:20:25 -0700
commit8c2b26e45cca45298627428a0bc8bf8a6423d9d1 (patch)
tree160dd35f77f9d4b14a3320de229b577befa9fc7a
parent0c5210f73e4a4d2d63e0f94b204bea531b56c529 (diff)
md/raid1: delay reads that could overtake behind-writes.
commit e555190d82c0f58e825e3cbd9e6ebe2e7ac713bd upstream. 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> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
-rw-r--r--drivers/md/bitmap.c4
-rw-r--r--drivers/md/bitmap.h3
-rw-r--r--drivers/md/raid1.c25
3 files changed, 24 insertions, 8 deletions
diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index a5e5f2fbf963..47831536deb1 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -1317,7 +1317,8 @@ 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);
}
@@ -1629,6 +1630,7 @@ 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 7e38d13ddcac..86950bc527af 100644
--- a/drivers/md/bitmap.h
+++ b/drivers/md/bitmap.h
@@ -254,6 +254,9 @@ struct bitmap {
wait_queue_head_t write_wait;
wait_queue_head_t overflow_wait;
+#ifndef __GENKSYMS__
+ wait_queue_head_t behind_wait;
+#endif
};
/* the bitmap API */
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 5ccad2822b11..791e1951430a 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -845,6 +845,15 @@ static int make_request(struct request_queue *q, 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);
@@ -922,9 +931,13 @@ static int make_request(struct request_queue *q, 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) < bitmap->max_write_behind &&
+ !waitqueue_active(&bitmap->behind_wait) &&
(behind_pages = alloc_behind_pages(bio)) != NULL)
set_bit(R1BIO_BehindIO, &r1_bio->state);
@@ -2105,15 +2118,13 @@ 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);