On Wednesday, October 12, 2005, Neil Brown [email protected] wrote:
>
> On Wednesday October 5, [email protected] wrote:
>> Please consider the following patch submittal
>> to insert rcu_dereference() to make explicit
>> the object of the rcu read-side critical sections.
>> Thank you.
>
> Thank for the patch and detailed explanations.
>
> I agree with all the places where you add rcu_dereference.
>
> I do not agree with the place you added rcu_assign_pointer.
> rdev->mddev is of no relevance to the rcu usage. However I think it
> is appropriate to use rcu_assign_pointer when setting the pointer that
> rcu_dereference dereferences. I had made appropriate changes.
>
> The place where you put the comment about incrementing new_disk does
> *not* require an increment. That loop actually runs backwards, and
> new_disk is decremented in the body of the loop.
>
> You moved 'rcu_read_unlock' down several lines in raid5.c, but didn't
> make an equivalent change in similar code in raid6main.c. I'm
> confident that this change isn't needed. After nr_pending has been
> incremented, there is no longer a need to hold the rcu read lock.
>
> I have improved the code in raid10.c so that the rcu_dereference'd
> pointer is held in a temporary variable, which is much cleaner than
> the existing code.
>
>
> My revised patch follows. I will submit it to Andrew if I hear
> nothing negative.
>
> Thanks,
> NeilBrown
This looks very good. Thank you for clarifying the implication of the
increment of nr_pending and for the rcu_assign_pointer() corrections.
Thank you.
Suzanne Wood
>
> -----
> Provide proper rcu_dereference / rcu_assign_pointer annotations in md
>
>
> Acked-by: <[email protected]>
> Signed-off-by: <[email protected]>
> Signed-off-by: Neil Brown <[email protected]>
>
> ### Diffstat output
> ./drivers/md/multipath.c | 8 ++++----
> ./drivers/md/raid1.c | 20 ++++++++++----------
> ./drivers/md/raid10.c | 30 ++++++++++++++++--------------
> ./drivers/md/raid5.c | 8 ++++----
> ./drivers/md/raid6main.c | 8 ++++----
> 5 files changed, 38 insertions(+), 36 deletions(-)
>
> diff ./drivers/md/multipath.c~current~ ./drivers/md/multipath.c
> --- ./drivers/md/multipath.c~current~ 2005-10-13 13:42:05.000000000 +1000
> +++ ./drivers/md/multipath.c 2005-10-13 13:49:39.000000000 +1000
> @@ -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();
> @@ -139,7 +139,7 @@ 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);
>
> @@ -228,7 +228,7 @@ 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);
> @@ -335,7 +335,7 @@ static int multipath_add_disk(mddev_t *m
> conf->working_disks++;
> rdev->raid_disk = path;
> rdev->in_sync = 1;
> - p->rdev = rdev;
> + rcu_assign_pointer(p->rdev, rdev);
> found = 1;
> }
>
>
> diff ./drivers/md/raid1.c~current~ ./drivers/md/raid1.c
> --- ./drivers/md/raid1.c~current~ 2005-10-13 13:42:05.000000000 +1000
> +++ ./drivers/md/raid1.c 2005-10-13 13:50:32.000000000 +1000
> @@ -416,10 +416,10 @@ static int read_balance(conf_t *conf, r1
> /* Choose the first operation device, for consistancy */
> new_disk = 0;
>
> - for (rdev = conf->mirrors[new_disk].rdev;
> + for (rdev = rcu_dereference(conf->mirrors[new_disk].rdev);
> !rdev || !rdev->in_sync
> || test_bit(WriteMostly, &rdev->flags);
> - rdev = conf->mirrors[++new_disk].rdev) {
> + rdev = rcu_dereference(conf->mirrors[++new_disk].rdev)) {
>
> if (rdev && rdev->in_sync)
> wonly_disk = new_disk;
> @@ -434,10 +434,10 @@ static int read_balance(conf_t *conf, r1
>
>
> /* make sure the disk is operational */
> - for (rdev = conf->mirrors[new_disk].rdev;
> + for (rdev = rcu_dereference(conf->mirrors[new_disk].rdev);
> !rdev || !rdev->in_sync ||
> test_bit(WriteMostly, &rdev->flags);
> - rdev = conf->mirrors[new_disk].rdev) {
> + rdev = rcu_dereference(conf->mirrors[new_disk].rdev)) {
>
> if (rdev && rdev->in_sync)
> wonly_disk = new_disk;
> @@ -474,7 +474,7 @@ static int read_balance(conf_t *conf, r1
> disk = conf->raid_disks;
> disk--;
>
> - rdev = conf->mirrors[disk].rdev;
> + rdev = rcu_dereference(conf->mirrors[disk].rdev);
>
> if (!rdev ||
> !rdev->in_sync ||
> @@ -496,7 +496,7 @@ static int read_balance(conf_t *conf, r1
>
>
> if (new_disk >= 0) {
> - rdev = conf->mirrors[new_disk].rdev;
> + rdev = rcu_dereference(conf->mirrors[new_disk].rdev);
> if (!rdev)
> goto retry;
> atomic_inc(&rdev->nr_pending);
> @@ -522,7 +522,7 @@ 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);
>
> @@ -556,7 +556,7 @@ 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);
> @@ -732,7 +732,7 @@ static int make_request(request_queue_t
> #endif
> rcu_read_lock();
> for (i = 0; i < disks; i++) {
> - if ((rdev=conf->mirrors[i].rdev) != NULL &&
> + if ((rdev=rcu_dereference(conf->mirrors[i].rdev)) != NULL &&
> !rdev->faulty) {
> atomic_inc(&rdev->nr_pending);
> if (rdev->faulty) {
> @@ -958,7 +958,7 @@ static int raid1_add_disk(mddev_t *mddev
> found = 1;
> if (rdev->saved_raid_disk != mirror)
> conf->fullsync = 1;
> - p->rdev = rdev;
> + rcu_assign_pointer(p->rdev, rdev);
> break;
> }
>
>
> diff ./drivers/md/raid10.c~current~ ./drivers/md/raid10.c
> --- ./drivers/md/raid10.c~current~ 2005-10-13 13:42:05.000000000 +1000
> +++ ./drivers/md/raid10.c 2005-10-13 14:09:29.000000000 +1000
> @@ -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)) == NULL ||
> + !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)) == NULL ||
> + !rdev->in_sync) {
> slot ++;
> if (slot == conf->copies) {
> disk = -1;
> @@ -547,11 +548,11 @@ 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)) == NULL ||
> + !rdev->in_sync)
> continue;
>
> - if (!atomic_read(&conf->mirrors[ndisk].rdev->nr_pending)) {
> + if (!atomic_read(&rdev->nr_pending)) {
> disk = ndisk;
> slot = nslot;
> break;
> @@ -569,7 +570,7 @@ rb_out:
> r10_bio->read_slot = slot;
> /* conf->next_seq_sect = this_sector + sectors;*/
>
> - if (disk >= 0 && conf->mirrors[disk].rdev)
> + if (disk >= 0 && (rdev=rcu_dereference(conf->mirrors[disk].rdev))!= NULL)
> atomic_inc(&conf->mirrors[disk].rdev->nr_pending);
> rcu_read_unlock();
>
> @@ -583,7 +584,7 @@ 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);
>
> @@ -614,7 +615,7 @@ 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);
> @@ -772,9 +773,10 @@ static int make_request(request_queue_t
> rcu_read_lock();
> for (i = 0; i < conf->copies; i++) {
> 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);
> + mdk_rdev_t *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;
> @@ -984,7 +986,7 @@ static int raid10_add_disk(mddev_t *mdde
> p->head_position = 0;
> rdev->raid_disk = mirror;
> found = 1;
> - p->rdev = rdev;
> + rcu_assign_pointer(p->rdev, rdev);
> break;
> }
>
>
> diff ./drivers/md/raid5.c~current~ ./drivers/md/raid5.c
> --- ./drivers/md/raid5.c~current~ 2005-10-13 13:42:05.000000000 +1000
> +++ ./drivers/md/raid5.c 2005-10-13 14:00:38.000000000 +1000
> @@ -1383,7 +1383,7 @@ 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)
> @@ -1457,7 +1457,7 @@ 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);
>
> @@ -1502,7 +1502,7 @@ 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);
> @@ -2178,7 +2178,7 @@ static int raid5_add_disk(mddev_t *mddev
> found = 1;
> if (rdev->saved_raid_disk != disk)
> conf->fullsync = 1;
> - p->rdev = rdev;
> + rcu_assign_pointer(p->rdev, rdev);
> break;
> }
> print_raid5_conf(conf);
>
> diff ./drivers/md/raid6main.c~current~ ./drivers/md/raid6main.c
> --- ./drivers/md/raid6main.c~current~ 2005-10-13 13:42:05.000000000 +1000
> +++ ./drivers/md/raid6main.c 2005-10-13 13:57:08.000000000 +1000
> @@ -1464,7 +1464,7 @@ 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)
> @@ -1538,7 +1538,7 @@ 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);
>
> @@ -1583,7 +1583,7 @@ 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);
> @@ -2158,7 +2158,7 @@ static int raid6_add_disk(mddev_t *mddev
> found = 1;
> if (rdev->saved_raid_disk != disk)
> conf->fullsync = 1;
> - p->rdev = rdev;
> + rcu_assign_pointer(p->rdev, rdev);
> break;
> }
> print_raid6_conf(conf);
>
-
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