Messages in this thread Patch in this message | | | Date | Sat, 4 Dec 2004 16:31:04 -0800 | From | "Paul E. McKenney" <> | Subject | [RFC, PATCH] RCU questions on md driver |
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Hello!
A few questions and comments on md driver locking, my best guess at answers may be found in the patch below (which I have not even attempted to compile, let alone test).
o Need some rcu_dereference() primitives in a number of places.
o The reference counts must be decremented after rcu_read_lock(). Otherwise, unless I am missing something, a preemption (in a CONFIG_PREEMPT kernel) occuring just before the rcu_read_lock() looks like it could destroy the element subsequently used.
o How does the locking work in read_balance() in drivers/md/raid1.c? It looks to me that the conf->mirrors[] array could potentially be changing during the read_balance() operation, which I cannot see how is handled correctly.
For that matter, I don't see what prevents multiple instances of read_balance() from executing concurrently on the same set of disks...
o Ditto for read_balance in drivers/md/raid10.c. And raid5.c.
Thoughts?
Thanx, Paul
diff -urpN -X ../dontdiff linux-2.5/drivers/md/multipath.c linux-2.5-mpio/drivers/md/multipath.c --- linux-2.5/drivers/md/multipath.c Mon Nov 29 10:48:55 2004 +++ linux-2.5-mpio/drivers/md/multipath.c Sat Dec 4 15:32:19 2004 @@ -63,7 +63,7 @@ static int multipath_map (multipath_conf rcu_read_lock(); for (i = 0; i < disks; i++) { - mdk_rdev_t *rdev = conf->multipaths[i].rdev; + mdk_rdev_t *rdev = rcu_dereference(conf->multipaths[i].rdev); if (rdev && rdev->in_sync) { atomic_inc(&rdev->nr_pending); rcu_read_unlock(); @@ -138,7 +138,7 @@ static void unplug_slaves(mddev_t *mddev rcu_read_lock(); for (i=0; i<mddev->raid_disks; i++) { - mdk_rdev_t *rdev = conf->multipaths[i].rdev; + mdk_rdev_t *rdev = rcu_dereference(conf->multipaths[i].rdev); if (rdev && !rdev->faulty && atomic_read(&rdev->nr_pending)) { request_queue_t *r_queue = bdev_get_queue(rdev->bdev); @@ -148,8 +148,8 @@ static void unplug_slaves(mddev_t *mddev if (r_queue->unplug_fn) r_queue->unplug_fn(r_queue); - rdev_dec_pending(rdev, mddev); rcu_read_lock(); + rdev_dec_pending(rdev, mddev); } } rcu_read_unlock(); @@ -222,7 +222,7 @@ static int multipath_issue_flush(request rcu_read_lock(); for (i=0; i<mddev->raid_disks && ret == 0; i++) { - mdk_rdev_t *rdev = conf->multipaths[i].rdev; + mdk_rdev_t *rdev = rcu_dereference(conf->multipaths[i].rdev); if (rdev && !rdev->faulty) { struct block_device *bdev = rdev->bdev; request_queue_t *r_queue = bdev_get_queue(bdev); @@ -234,8 +234,8 @@ static int multipath_issue_flush(request rcu_read_unlock(); ret = r_queue->issue_flush_fn(r_queue, bdev->bd_disk, error_sector); - rdev_dec_pending(rdev, mddev); rcu_read_lock(); + rdev_dec_pending(rdev, mddev); } } } diff -urpN -X ../dontdiff linux-2.5/drivers/md/raid1.c linux-2.5-mpio/drivers/md/raid1.c --- linux-2.5/drivers/md/raid1.c Mon Nov 29 10:48:55 2004 +++ linux-2.5-mpio/drivers/md/raid1.c Sat Dec 4 16:16:48 2004 @@ -338,6 +338,7 @@ static int read_balance(conf_t *conf, r1 int new_disk = conf->last_used, disk = new_disk; const int sectors = r1_bio->sectors; sector_t new_distance, current_distance; + mdk_rdev_t *rdev; rcu_read_lock(); /* @@ -350,8 +351,9 @@ static int read_balance(conf_t *conf, r1 /* Choose the first operation device, for consistancy */ new_disk = 0; - while (!conf->mirrors[new_disk].rdev || - !conf->mirrors[new_disk].rdev->in_sync) { + while (!(rdev = + rcu_dereference(conf->mirrors[new_disk].rdev)) || + !rdev->in_sync) { new_disk++; if (new_disk == conf->raid_disks) { new_disk = -1; @@ -363,8 +365,8 @@ static int read_balance(conf_t *conf, r1 /* make sure the disk is operational */ - while (!conf->mirrors[new_disk].rdev || - !conf->mirrors[new_disk].rdev->in_sync) { + while (!(rdev = rcu_dereference(conf->mirrors[new_disk].rdev)) || + !rdev->in_sync) { if (new_disk <= 0) new_disk = conf->raid_disks; new_disk--; @@ -393,11 +395,11 @@ static int read_balance(conf_t *conf, r1 disk = conf->raid_disks; disk--; - if (!conf->mirrors[disk].rdev || - !conf->mirrors[disk].rdev->in_sync) + if (!(rdev = rcu_dereference(conf->mirrors[disk].rdev)) || + !rdev->in_sync) continue; - if (!atomic_read(&conf->mirrors[disk].rdev->nr_pending)) { + if (!atomic_read(&rdev->nr_pending)) { new_disk = disk; break; } @@ -414,7 +416,7 @@ rb_out: if (new_disk >= 0) { conf->next_seq_sect = this_sector + sectors; conf->last_used = new_disk; - atomic_inc(&conf->mirrors[new_disk].rdev->nr_pending); + atomic_inc(&rdev->nr_pending); } rcu_read_unlock(); @@ -428,7 +430,7 @@ static void unplug_slaves(mddev_t *mddev rcu_read_lock(); for (i=0; i<mddev->raid_disks; i++) { - mdk_rdev_t *rdev = conf->mirrors[i].rdev; + mdk_rdev_t *rdev = rcu_dereference(conf->mirrors[i].rdev); if (rdev && !rdev->faulty && atomic_read(&rdev->nr_pending)) { request_queue_t *r_queue = bdev_get_queue(rdev->bdev); @@ -438,8 +440,8 @@ static void unplug_slaves(mddev_t *mddev if (r_queue->unplug_fn) r_queue->unplug_fn(r_queue); - rdev_dec_pending(rdev, mddev); rcu_read_lock(); + rdev_dec_pending(rdev, mddev); } } rcu_read_unlock(); @@ -459,7 +461,7 @@ static int raid1_issue_flush(request_que rcu_read_lock(); for (i=0; i<mddev->raid_disks && ret == 0; i++) { - mdk_rdev_t *rdev = conf->mirrors[i].rdev; + mdk_rdev_t *rdev = rcu_dereference(conf->mirrors[i].rdev); if (rdev && !rdev->faulty) { struct block_device *bdev = rdev->bdev; request_queue_t *r_queue = bdev_get_queue(bdev); @@ -471,8 +473,8 @@ static int raid1_issue_flush(request_que rcu_read_unlock(); ret = r_queue->issue_flush_fn(r_queue, bdev->bd_disk, error_sector); - rdev_dec_pending(rdev, mddev); rcu_read_lock(); + rdev_dec_pending(rdev, mddev); } } } @@ -585,9 +587,9 @@ static int make_request(request_queue_t disks = conf->raid_disks; rcu_read_lock(); for (i = 0; i < disks; i++) { - if (conf->mirrors[i].rdev && - !conf->mirrors[i].rdev->faulty) { - atomic_inc(&conf->mirrors[i].rdev->nr_pending); + mdk_rdev_t *rdev = rcu_dereference(conf->mirrors[i].rdev); + if (rdev && !rdev->faulty) { + atomic_inc(&rdev->nr_pending); r1_bio->bios[i] = bio; } else r1_bio->bios[i] = NULL; diff -urpN -X ../dontdiff linux-2.5/drivers/md/raid10.c linux-2.5-mpio/drivers/md/raid10.c --- linux-2.5/drivers/md/raid10.c Mon Nov 29 10:48:55 2004 +++ linux-2.5-mpio/drivers/md/raid10.c Sat Dec 4 16:23:49 2004 @@ -496,6 +496,7 @@ static int read_balance(conf_t *conf, r1 int disk, slot, nslot; const int sectors = r10_bio->sectors; sector_t new_distance, current_distance; + mdk_rdev_t *rdev; raid10_find_phys(conf, r10_bio); rcu_read_lock(); @@ -510,8 +511,8 @@ static int read_balance(conf_t *conf, r1 slot = 0; disk = r10_bio->devs[slot].devnum; - while (!conf->mirrors[disk].rdev || - !conf->mirrors[disk].rdev->in_sync) { + while (!(rdev = rcu_dereference(conf->mirrors[disk].rdev)) || + !rdev->in_sync) { slot++; if (slot == conf->copies) { slot = 0; @@ -527,8 +528,8 @@ static int read_balance(conf_t *conf, r1 /* make sure the disk is operational */ slot = 0; disk = r10_bio->devs[slot].devnum; - while (!conf->mirrors[disk].rdev || - !conf->mirrors[disk].rdev->in_sync) { + while (!(rdev = rcu_dereference(conf->mirrors[disk].rdev)) || + !rdev->in_sync) { slot ++; if (slot == conf->copies) { disk = -1; @@ -546,11 +547,11 @@ static int read_balance(conf_t *conf, r1 int ndisk = r10_bio->devs[nslot].devnum; - if (!conf->mirrors[ndisk].rdev || - !conf->mirrors[ndisk].rdev->in_sync) + if (!(rdev = rcu_dereference(conf->mirrors[ndisk].rdev)) || + !rdev->in_sync) continue; - if (!atomic_read(&conf->mirrors[ndisk].rdev->nr_pending)) { + if (!atomic_read(&rdev->nr_pending)) { disk = ndisk; slot = nslot; break; @@ -568,8 +569,8 @@ rb_out: r10_bio->read_slot = slot; /* conf->next_seq_sect = this_sector + sectors;*/ - if (disk >= 0 && conf->mirrors[disk].rdev) - atomic_inc(&conf->mirrors[disk].rdev->nr_pending); + if (disk >= 0 && rdev) + atomic_inc(&rdev->nr_pending); rcu_read_unlock(); return disk; @@ -582,7 +583,7 @@ static void unplug_slaves(mddev_t *mddev rcu_read_lock(); for (i=0; i<mddev->raid_disks; i++) { - mdk_rdev_t *rdev = conf->mirrors[i].rdev; + mdk_rdev_t *rdev = rcu_dereference(conf->mirrors[i].rdev); if (rdev && !rdev->faulty && atomic_read(&rdev->nr_pending)) { request_queue_t *r_queue = bdev_get_queue(rdev->bdev); @@ -592,8 +593,8 @@ static void unplug_slaves(mddev_t *mddev if (r_queue->unplug_fn) r_queue->unplug_fn(r_queue); - rdev_dec_pending(rdev, mddev); rcu_read_lock(); + rdev_dec_pending(rdev, mddev); } } rcu_read_unlock(); @@ -613,7 +614,7 @@ static int raid10_issue_flush(request_qu rcu_read_lock(); for (i=0; i<mddev->raid_disks && ret == 0; i++) { - mdk_rdev_t *rdev = conf->mirrors[i].rdev; + mdk_rdev_t *rdev = rcu_dereference(conf->mirrors[i].rdev); if (rdev && !rdev->faulty) { struct block_device *bdev = rdev->bdev; request_queue_t *r_queue = bdev_get_queue(bdev); @@ -625,8 +626,8 @@ static int raid10_issue_flush(request_qu rcu_read_unlock(); ret = r_queue->issue_flush_fn(r_queue, bdev->bd_disk, error_sector); - rdev_dec_pending(rdev, mddev); rcu_read_lock(); + rdev_dec_pending(rdev, mddev); } } } @@ -763,10 +764,11 @@ static int make_request(request_queue_t raid10_find_phys(conf, r10_bio); rcu_read_lock(); for (i = 0; i < conf->copies; i++) { + mdk_rdev_t *rdev; int d = r10_bio->devs[i].devnum; - if (conf->mirrors[d].rdev && - !conf->mirrors[d].rdev->faulty) { - atomic_inc(&conf->mirrors[d].rdev->nr_pending); + rdev = rcu_dereference(conf->mirrors[d].rdev); + if (rdev && !rdev->faulty) { + atomic_inc(&rdev->nr_pending); r10_bio->devs[i].bio = bio; } else r10_bio->devs[i].bio = NULL; diff -urpN -X ../dontdiff linux-2.5/drivers/md/raid5.c linux-2.5-mpio/drivers/md/raid5.c --- linux-2.5/drivers/md/raid5.c Mon Nov 29 10:48:55 2004 +++ linux-2.5-mpio/drivers/md/raid5.c Sat Dec 4 16:26:01 2004 @@ -1248,7 +1248,7 @@ static void handle_stripe(struct stripe_ bi->bi_end_io = raid5_end_read_request; rcu_read_lock(); - rdev = conf->disks[i].rdev; + rdev = rcu_dereference(conf->disks[i].rdev); if (rdev && rdev->faulty) rdev = NULL; if (rdev) @@ -1305,7 +1305,7 @@ static void unplug_slaves(mddev_t *mddev rcu_read_lock(); for (i=0; i<mddev->raid_disks; i++) { - mdk_rdev_t *rdev = conf->disks[i].rdev; + mdk_rdev_t *rdev = rcu_dereference(conf->disks[i].rdev); if (rdev && !rdev->faulty && atomic_read(&rdev->nr_pending)) { request_queue_t *r_queue = bdev_get_queue(rdev->bdev); @@ -1315,8 +1315,8 @@ static void unplug_slaves(mddev_t *mddev if (r_queue->unplug_fn) r_queue->unplug_fn(r_queue); - rdev_dec_pending(rdev, mddev); rcu_read_lock(); + rdev_dec_pending(rdev, mddev); } } rcu_read_unlock(); @@ -1348,7 +1348,7 @@ static int raid5_issue_flush(request_que rcu_read_lock(); for (i=0; i<mddev->raid_disks && ret == 0; i++) { - mdk_rdev_t *rdev = conf->disks[i].rdev; + mdk_rdev_t *rdev = rcu_dereference(conf->disks[i].rdev); if (rdev && !rdev->faulty) { struct block_device *bdev = rdev->bdev; request_queue_t *r_queue = bdev_get_queue(bdev); @@ -1360,8 +1360,8 @@ static int raid5_issue_flush(request_que rcu_read_unlock(); ret = r_queue->issue_flush_fn(r_queue, bdev->bd_disk, error_sector); - rdev_dec_pending(rdev, mddev); rcu_read_lock(); + rdev_dec_pending(rdev, mddev); } } } diff -urpN -X ../dontdiff linux-2.5/drivers/md/raid6main.c linux-2.5-mpio/drivers/md/raid6main.c --- linux-2.5/drivers/md/raid6main.c Mon Nov 29 10:48:55 2004 +++ linux-2.5-mpio/drivers/md/raid6main.c Sat Dec 4 16:27:56 2004 @@ -1411,7 +1411,7 @@ static void handle_stripe(struct stripe_ bi->bi_end_io = raid6_end_read_request; rcu_read_lock(); - rdev = conf->disks[i].rdev; + rdev = rcu_dereference(conf->disks[i].rdev); if (rdev && rdev->faulty) rdev = NULL; if (rdev) @@ -1468,7 +1468,7 @@ static void unplug_slaves(mddev_t *mddev rcu_read_lock(); for (i=0; i<mddev->raid_disks; i++) { - mdk_rdev_t *rdev = conf->disks[i].rdev; + mdk_rdev_t *rdev = rcu_dereference(conf->disks[i].rdev); if (rdev && !rdev->faulty && atomic_read(&rdev->nr_pending)) { request_queue_t *r_queue = bdev_get_queue(rdev->bdev); @@ -1478,8 +1478,8 @@ static void unplug_slaves(mddev_t *mddev if (r_queue->unplug_fn) r_queue->unplug_fn(r_queue); - rdev_dec_pending(rdev, mddev); rcu_read_lock(); + rdev_dec_pending(rdev, mddev); } } rcu_read_unlock(); @@ -1511,7 +1511,7 @@ static int raid6_issue_flush(request_que rcu_read_lock(); for (i=0; i<mddev->raid_disks && ret == 0; i++) { - mdk_rdev_t *rdev = conf->disks[i].rdev; + mdk_rdev_t *rdev = rcu_dereference(conf->disks[i].rdev); if (rdev && !rdev->faulty) { struct block_device *bdev = rdev->bdev; request_queue_t *r_queue = bdev_get_queue(bdev); @@ -1523,8 +1523,8 @@ static int raid6_issue_flush(request_que rcu_read_unlock(); ret = r_queue->issue_flush_fn(r_queue, bdev->bd_disk, error_sector); - rdev_dec_pending(rdev, mddev); rcu_read_lock(); + rdev_dec_pending(rdev, mddev); } } } - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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