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md/raid10: Remove unnecessary rcu_dereference in raid10_handle_discard

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We are seeing the following warning in raid10_handle_discard.
[  695.110751] =============================
[  695.131439] WARNING: suspicious RCU usage
[  695.151389] 4.18.0-319.el8.x86_64+debug #1 Not tainted
[  695.174413] -----------------------------
[  695.192603] drivers/md/raid10.c:1776 suspicious
rcu_dereference_check() usage!
[  695.225107] other info that might help us debug this:
[  695.260940] rcu_scheduler_active = 2, debug_locks = 1
[  695.290157] no locks held by mkfs.xfs/10186.

In the first loop of function raid10_handle_discard. It already
determines which disk need to handle discard request and add the
rdev reference count rdev->nr_pending. So the conf->mirrors will
not change until all bios come back from underlayer disks. It
doesn't need to use rcu_dereference to get rdev.

Cc: stable@vger.kernel.org
Fixes: d30588b273 ('md/raid10: improve raid10 discard request')
Signed-off-by: Xiao Ni <xni@redhat.com>
Acked-by: Guoqing Jiang <guoqing.jiang@linux.dev>
Signed-off-by: Song Liu <songliubraving@fb.com>
This commit is contained in:
Xiao Ni 2021-08-18 13:57:48 +08:00 committed by Song Liu
parent 7ee656c3ac
commit 46d4703b1d
1 changed files with 10 additions and 4 deletions
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14
drivers/md/raid10.c
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@ -1712,6 +1712,11 @@ retry_discard:
} else } else
r10_bio->master_bio = (struct bio *)first_r10bio; r10_bio->master_bio = (struct bio *)first_r10bio;
/*
* first select target devices under rcu_lock and
* inc refcount on their rdev. Record them by setting
* bios[x] to bio
*/
rcu_read_lock(); rcu_read_lock();
for (disk = 0; disk < geo->raid_disks; disk++) { for (disk = 0; disk < geo->raid_disks; disk++) {
struct md_rdev *rdev = rcu_dereference(conf->mirrors[disk].rdev); struct md_rdev *rdev = rcu_dereference(conf->mirrors[disk].rdev);
@ -1743,9 +1748,6 @@ retry_discard:
for (disk = 0; disk < geo->raid_disks; disk++) { for (disk = 0; disk < geo->raid_disks; disk++) {
sector_t dev_start, dev_end; sector_t dev_start, dev_end;
struct bio *mbio, *rbio = NULL; struct bio *mbio, *rbio = NULL;
struct md_rdev *rdev = rcu_dereference(conf->mirrors[disk].rdev);
struct md_rdev *rrdev = rcu_dereference(
conf->mirrors[disk].replacement);
/* /*
* Now start to calculate the start and end address for each disk. * Now start to calculate the start and end address for each disk.
@ -1775,9 +1777,12 @@ retry_discard:
/* /*
* It only handles discard bio which size is >= stripe size, so * It only handles discard bio which size is >= stripe size, so
* dev_end > dev_start all the time * dev_end > dev_start all the time.
* It doesn't need to use rcu lock to get rdev here. We already
* add rdev->nr_pending in the first loop.
*/ */
if (r10_bio->devs[disk].bio) { if (r10_bio->devs[disk].bio) {
struct md_rdev *rdev = conf->mirrors[disk].rdev;
mbio = bio_clone_fast(bio, GFP_NOIO, &mddev->bio_set); mbio = bio_clone_fast(bio, GFP_NOIO, &mddev->bio_set);
mbio->bi_end_io = raid10_end_discard_request; mbio->bi_end_io = raid10_end_discard_request;
mbio->bi_private = r10_bio; mbio->bi_private = r10_bio;
@ -1790,6 +1795,7 @@ retry_discard:
bio_endio(mbio); bio_endio(mbio);
} }
if (r10_bio->devs[disk].repl_bio) { if (r10_bio->devs[disk].repl_bio) {
struct md_rdev *rrdev = conf->mirrors[disk].replacement;
rbio = bio_clone_fast(bio, GFP_NOIO, &mddev->bio_set); rbio = bio_clone_fast(bio, GFP_NOIO, &mddev->bio_set);
rbio->bi_end_io = raid10_end_discard_request; rbio->bi_end_io = raid10_end_discard_request;
rbio->bi_private = r10_bio; rbio->bi_private = r10_bio;