linux-kernel - Re: [PATCH -next 0/6] md: remvoe rcu protection to access rdev from conf

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Date:   Thu, 19 Oct 2023 09:59:37 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     Yu Kuai <yukuai1@...weicloud.com>, Song Liu <song@...nel.org>
Cc:     linux-raid@...r.kernel.org, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com, yangerkun@...wei.com,
        "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH -next 0/6] md: remvoe rcu protection to access rdev from
 conf

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@...weicloud.com> wrote:
>>>
>>> From: Yu Kuai <yukuai3@...wei.com>
>>>
>>> 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
>>>
>> .
>>
> 
> .
>