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authorXiao Ni <xni@redhat.com>2021-08-18 07:57:48 +0200
committerSong Liu <songliubraving@fb.com>2021-08-26 18:04:15 +0200
commit46d4703b1db4c86ab5acb2331b10df999f005e8e (patch)
tree322f0fd2d0c863d44d4637ad22809928a763adea /drivers/md/raid10.c
parentnbd: remove nbd->destroy_complete (diff)
downloadlinux-46d4703b1db4c86ab5acb2331b10df999f005e8e.tar.xz
linux-46d4703b1db4c86ab5acb2331b10df999f005e8e.zip
md/raid10: Remove unnecessary rcu_dereference in raid10_handle_discard
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: d30588b2731f ('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>
Diffstat (limited to '')
-rw-r--r--drivers/md/raid10.c14
1 files changed, 10 insertions, 4 deletions
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 16977e8e075d..d5d92337e35e 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1712,6 +1712,11 @@ retry_discard:
} else
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();
for (disk = 0; disk < geo->raid_disks; disk++) {
struct md_rdev *rdev = rcu_dereference(conf->mirrors[disk].rdev);
@@ -1743,9 +1748,6 @@ retry_discard:
for (disk = 0; disk < geo->raid_disks; disk++) {
sector_t dev_start, dev_end;
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.
@@ -1775,9 +1777,12 @@ retry_discard:
/*
* 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) {
+ struct md_rdev *rdev = conf->mirrors[disk].rdev;
mbio = bio_clone_fast(bio, GFP_NOIO, &mddev->bio_set);
mbio->bi_end_io = raid10_end_discard_request;
mbio->bi_private = r10_bio;
@@ -1790,6 +1795,7 @@ retry_discard:
bio_endio(mbio);
}
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->bi_end_io = raid10_end_discard_request;
rbio->bi_private = r10_bio;