From 8c2b26e45cca45298627428a0bc8bf8a6423d9d1 Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Wed, 31 Mar 2010 11:21:44 +1100 Subject: 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 Signed-off-by: Greg Kroah-Hartman --- drivers/md/bitmap.c | 4 +++- drivers/md/bitmap.h | 3 +++ drivers/md/raid1.c | 25 ++++++++++++++++++------- 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); -- cgit v1.2.3