Hi,
在 2023/10/19 9:04, Yu Kuai 写道:
Hi,
在 2023/10/19 1:58, Song Liu 写道:
On Sun, Oct 15, 2023 at 6:28 PM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
From: Yu Kuai <yukuai3@xxxxxxxxxx>
Yu Kuai (6):
md: remove useless debug code to print configuration
md: remove flag RemoveSynchronized
md/raid1: remove rcu protection to access rdev from conf
md/raid10: remove rcu protection to access rdev from conf
md/raid5: remove rcu protection to access rdev from conf
md/md-multipath: remove rcu protection to access rdev from conf
While a cover letter is highly recommended for a patchset. An empty
cover letter like this doesn't really add value. If the description of
each
patch is clear enough, it is OK to not have a cover-letter.
Yes, I was hoping commit message in each patch is clear enough,I'll try
to explain everything more detailed.
I'll add following cover letter in the next version:
The lifetime of rdev:
1. md_import_device() generate a rdev based on underlying disk;
mddev_lock()
rdev = kzalloc();
rdev->bdev = blkdev_get_by_dev();
mddev_unlock()
2. bind_rdev_to_array() add this rdev to mddev->disks;
mddev_lock()
kobject_add(&rdev->kobj, &mddev->kobj, ...);
list_add_rcu(&rdev->same_set, &mddev->disks);
mddev_unlock()
3. remove_and_add_spares() add this rdev to conf;
mddev_lock()
rdev_addable();
pers->hot_add_disk();
rcu_assign_pointer(conf->rdev, rdev);
mddev_unlock()
4. Use this array with rdev;
5. remove_and_add_spares() remove rdev from conf;
// triggered by sysfs/ioctl
mddev_lock()
rdev_removeable();
pers->hot_remove_disk();
rcu_assign_pointer(conf->rdev, NULL);
synchronize_rcu();
mddev_unlock()
// triggered by deamon
mddev_lock()
rdev_removeable();
synchronize_rcu(); -> this can't protect accessing rdev from conf
pers->hot_remove_disk();
rcu_assign_pointer(conf->rdev, NULL);
mddev_unlock()
6. md_kick_rdev_from_array() remove rdev from mddev->disks;
mddev_lock()
list_del_rcu(&rdev->same_set);
synchronize_rcu();
list_add(&rdev->same_set, &mddev->deleting)
mddev_unlock()
export_rdev
There are two seperate rcu protection for rdev, and this pathset remove
the protection of conf(step 3 and 5), because it's safe to access rdev
from conf in following cases:
- If 'reconfig_mutex' is held, because rdev can't be added or rmoved to
conf;
- If there is normal IO inflight, because mddev_suspend() will prevent
rdev to be added or removed to conf;
- If sync thread is running, because remove_and_add_spares() can only
be called from daemon thread when sync thread is done, and
'MD_RECOVERY_RUNNING' is also checked for ioctl/sysfs;
- if rcu_read_lock() or any spinlock is held, because synchronize_rcu()
from step 6 prevent rdev to be freed until rcu_read_unlock() or
spinlock is released;
Thanks,
Kuai
Thanks,
Kuai
Thanks,
Song
drivers/md/md-multipath.c | 29 ++---
drivers/md/md.c | 37 +-----
drivers/md/raid1.c | 94 ++++-----------
drivers/md/raid10.c | 248 +++++++++-----------------------------
drivers/md/raid5-cache.c | 11 +-
drivers/md/raid5-ppl.c | 16 +--
drivers/md/raid5.c | 225 ++++++++++------------------------
drivers/md/raid5.h | 4 +-
8 files changed, 163 insertions(+), 501 deletions(-)
--
2.39.2
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