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| author | NeilBrown <neilb@suse.com> | 2018-02-02 23:19:30 +0100 |
|---|---|---|
| committer | Shaohua Li <sh.li@alibaba-inc.com> | 2018-02-18 19:22:27 +0100 |
| commit | f2785b527cda46314805123ddcbc871655b7c4c4 (patch) | |
| tree | 797db5c31d88db7c308e660356501d1367c4cab8 /drivers/md/raid5.h | |
| parent | md: fix md_write_start() deadlock w/o metadata devices (diff) | |
| download | linux-f2785b527cda46314805123ddcbc871655b7c4c4.tar.xz linux-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/raid5.h')
| -rw-r--r-- | drivers/md/raid5.h | 12 |
1 files changed, 12 insertions, 0 deletions
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 */ |