md linear: Protecting mddev with rcu locks to avoid races
Due to the lack of memory ordering guarantees, we may have races around mddev->conf. In particular, the correct contents of the structure we get from dereferencing ->private might not be visible to this CPU yet, and they might not be correct w.r.t mddev->raid_disks. This patch addresses the problem using rcu protection to avoid such race conditions. Signed-off-by: SandeepKsinha <sandeepksinha@gmail.com> Signed-off-by: NeilBrown <neilb@suse.de>
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@ -28,10 +28,11 @@
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static inline dev_info_t *which_dev(mddev_t *mddev, sector_t sector)
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{
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int lo, mid, hi;
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linear_conf_t *conf = mddev->private;
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linear_conf_t *conf;
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lo = 0;
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hi = mddev->raid_disks - 1;
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conf = rcu_dereference(mddev->private);
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/*
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* Binary Search
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@ -66,8 +67,10 @@ static int linear_mergeable_bvec(struct request_queue *q,
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unsigned long maxsectors, bio_sectors = bvm->bi_size >> 9;
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sector_t sector = bvm->bi_sector + get_start_sect(bvm->bi_bdev);
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rcu_read_lock();
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dev0 = which_dev(mddev, sector);
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maxsectors = dev0->end_sector - sector;
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rcu_read_unlock();
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if (maxsectors < bio_sectors)
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maxsectors = 0;
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@ -86,36 +89,50 @@ static int linear_mergeable_bvec(struct request_queue *q,
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static void linear_unplug(struct request_queue *q)
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{
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mddev_t *mddev = q->queuedata;
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linear_conf_t *conf = mddev->private;
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linear_conf_t *conf;
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int i;
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rcu_read_lock();
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conf = rcu_dereference(mddev->private);
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for (i=0; i < mddev->raid_disks; i++) {
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struct request_queue *r_queue = bdev_get_queue(conf->disks[i].rdev->bdev);
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blk_unplug(r_queue);
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}
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rcu_read_unlock();
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}
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static int linear_congested(void *data, int bits)
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{
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mddev_t *mddev = data;
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linear_conf_t *conf = mddev->private;
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linear_conf_t *conf;
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int i, ret = 0;
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rcu_read_lock();
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conf = rcu_dereference(mddev->private);
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for (i = 0; i < mddev->raid_disks && !ret ; i++) {
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struct request_queue *q = bdev_get_queue(conf->disks[i].rdev->bdev);
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ret |= bdi_congested(&q->backing_dev_info, bits);
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}
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rcu_read_unlock();
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return ret;
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}
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static sector_t linear_size(mddev_t *mddev, sector_t sectors, int raid_disks)
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{
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linear_conf_t *conf = mddev->private;
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linear_conf_t *conf;
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sector_t array_sectors;
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rcu_read_lock();
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conf = rcu_dereference(mddev->private);
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WARN_ONCE(sectors || raid_disks,
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"%s does not support generic reshape\n", __func__);
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array_sectors = conf->array_sectors;
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rcu_read_unlock();
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return conf->array_sectors;
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return array_sectors;
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}
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static linear_conf_t *linear_conf(mddev_t *mddev, int raid_disks)
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@ -229,8 +246,8 @@ static int linear_add(mddev_t *mddev, mdk_rdev_t *rdev)
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return -ENOMEM;
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newconf->prev = mddev->private;
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mddev->private = newconf;
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mddev->raid_disks++;
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rcu_assign_pointer(mddev->private, newconf);
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md_set_array_sectors(mddev, linear_size(mddev, 0, 0));
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set_capacity(mddev->gendisk, mddev->array_sectors);
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return 0;
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@ -240,6 +257,12 @@ static int linear_stop (mddev_t *mddev)
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{
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linear_conf_t *conf = mddev->private;
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/*
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* We do not require rcu protection here since
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* we hold reconfig_mutex for both linear_add and
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* linear_stop, so they cannot race.
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*/
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blk_sync_queue(mddev->queue); /* the unplug fn references 'conf'*/
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do {
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linear_conf_t *t = conf->prev;
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@ -269,9 +292,11 @@ static int linear_make_request (struct request_queue *q, struct bio *bio)
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bio_sectors(bio));
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part_stat_unlock();
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rcu_read_lock();
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tmp_dev = which_dev(mddev, bio->bi_sector);
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start_sector = tmp_dev->end_sector - tmp_dev->rdev->sectors;
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if (unlikely(bio->bi_sector >= (tmp_dev->end_sector)
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|| (bio->bi_sector < start_sector))) {
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char b[BDEVNAME_SIZE];
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@ -282,6 +307,7 @@ static int linear_make_request (struct request_queue *q, struct bio *bio)
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bdevname(tmp_dev->rdev->bdev, b),
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(unsigned long long)tmp_dev->rdev->sectors,
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(unsigned long long)start_sector);
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rcu_read_unlock();
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bio_io_error(bio);
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return 0;
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}
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@ -291,9 +317,11 @@ static int linear_make_request (struct request_queue *q, struct bio *bio)
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* split it.
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*/
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struct bio_pair *bp;
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sector_t end_sector = tmp_dev->end_sector;
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bp = bio_split(bio,
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tmp_dev->end_sector - bio->bi_sector);
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rcu_read_unlock();
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bp = bio_split(bio, end_sector - bio->bi_sector);
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if (linear_make_request(q, &bp->bio1))
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generic_make_request(&bp->bio1);
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@ -306,6 +334,7 @@ static int linear_make_request (struct request_queue *q, struct bio *bio)
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bio->bi_bdev = tmp_dev->rdev->bdev;
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bio->bi_sector = bio->bi_sector - start_sector
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+ tmp_dev->rdev->data_offset;
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rcu_read_unlock();
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return 1;
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}
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