diff options
author | NeilBrown <neilb@suse.com> | 2018-02-03 09:19:30 +1100 |
---|---|---|
committer | Shaohua Li <sh.li@alibaba-inc.com> | 2018-02-18 10:22:27 -0800 |
commit | f2785b527cda46314805123ddcbc871655b7c4c4 (patch) | |
tree | 797db5c31d88db7c308e660356501d1367c4cab8 /drivers/md | |
parent | 4b6c1060eaa6495aa5b0032e8f2d51dd936b1257 (diff) | |
download | linux-stable-f2785b527cda46314805123ddcbc871655b7c4c4.tar.gz linux-stable-f2785b527cda46314805123ddcbc871655b7c4c4.tar.bz2 linux-stable-f2785b527cda46314805123ddcbc871655b7c4c4.zip |
md: document lifetime of internal rdev pointer.
The rdev pointer kept in the local 'config' for each for
raid1, raid10, raid4/5/6 has non-obvious lifetime rules.
Sometimes RCU is needed, sometimes a lock, something nothing.
Add documentation to explain this.
Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <sh.li@alibaba-inc.com>
Diffstat (limited to 'drivers/md')
-rw-r--r-- | drivers/md/raid1.h | 12 | ||||
-rw-r--r-- | drivers/md/raid10.h | 13 | ||||
-rw-r--r-- | drivers/md/raid5.h | 12 |
3 files changed, 37 insertions, 0 deletions
diff --git a/drivers/md/raid1.h b/drivers/md/raid1.h index c7294e7557e0..eb84bc68e2fd 100644 --- a/drivers/md/raid1.h +++ b/drivers/md/raid1.h @@ -26,6 +26,18 @@ #define BARRIER_BUCKETS_NR_BITS (PAGE_SHIFT - ilog2(sizeof(atomic_t))) #define BARRIER_BUCKETS_NR (1<<BARRIER_BUCKETS_NR_BITS) +/* Note: raid1_info.rdev can be set to NULL asynchronously by raid1_remove_disk. + * There are three safe ways to access raid1_info.rdev. + * 1/ when holding mddev->reconfig_mutex + * 2/ when resync/recovery is known to be happening - i.e. in code that is + * called as part of performing resync/recovery. + * 3/ while holding rcu_read_lock(), use rcu_dereference to get the pointer + * and if it is non-NULL, increment rdev->nr_pending before dropping the + * RCU lock. + * When .rdev is set to NULL, the nr_pending count checked again and if it has + * been incremented, the pointer is put back in .rdev. + */ + struct raid1_info { struct md_rdev *rdev; sector_t head_position; diff --git a/drivers/md/raid10.h b/drivers/md/raid10.h index db2ac22ac1b4..e2e8840de9bf 100644 --- a/drivers/md/raid10.h +++ b/drivers/md/raid10.h @@ -2,6 +2,19 @@ #ifndef _RAID10_H #define _RAID10_H +/* Note: raid10_info.rdev can be set to NULL asynchronously by + * raid10_remove_disk. + * There are three safe ways to access raid10_info.rdev. + * 1/ when holding mddev->reconfig_mutex + * 2/ when resync/recovery/reshape is known to be happening - i.e. in code + * that is called as part of performing resync/recovery/reshape. + * 3/ while holding rcu_read_lock(), use rcu_dereference to get the pointer + * and if it is non-NULL, increment rdev->nr_pending before dropping the + * RCU lock. + * When .rdev is set to NULL, the nr_pending count checked again and if it has + * been incremented, the pointer is put back in .rdev. + */ + struct raid10_info { struct md_rdev *rdev, *replacement; sector_t head_position; diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h index 2e6123825095..3f8da26032ac 100644 --- a/drivers/md/raid5.h +++ b/drivers/md/raid5.h @@ -450,6 +450,18 @@ enum { * HANDLE gets cleared if stripe_handle leaves nothing locked. */ +/* Note: disk_info.rdev can be set to NULL asynchronously by raid5_remove_disk. + * There are three safe ways to access disk_info.rdev. + * 1/ when holding mddev->reconfig_mutex + * 2/ when resync/recovery/reshape is known to be happening - i.e. in code that + * is called as part of performing resync/recovery/reshape. + * 3/ while holding rcu_read_lock(), use rcu_dereference to get the pointer + * and if it is non-NULL, increment rdev->nr_pending before dropping the RCU + * lock. + * When .rdev is set to NULL, the nr_pending count checked again and if + * it has been incremented, the pointer is put back in .rdev. + */ + struct disk_info { struct md_rdev *rdev, *replacement; struct page *extra_page; /* extra page to use in prexor */ |