Messages in this thread | | | Subject | Re: [PATCH -next v2 1/6] md: remove useless debug code to print configuration | From | Yu Kuai <> | Date | Sat, 25 Nov 2023 14:50:02 +0800 |
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Hi,
在 2023/11/25 0:49, Song Liu 写道: > On Fri, Nov 24, 2023 at 1:12 AM Yu Kuai <yukuai1@huaweicloud.com> wrote: >> >> Hi, >> >> 在 2023/11/24 16:17, Song Liu 写道: >>> On Fri, Oct 20, 2023 at 7:25 PM Yu Kuai <yukuai1@huaweicloud.com> wrote: >>>> >>>> From: Yu Kuai <yukuai3@huawei.com> >>>> >>>> One the one hand, print_conf() can be called without grabbing >>>> 'reconfig_mtuex' and current rcu protection to access rdev through 'conf' >>>> is not safe. Fortunately, there is a separate rcu protection to access >>>> rdev from 'mddev->disks', and rdev is always removed from 'conf' before >>>> 'mddev->disks'. >>>> >>>> On the other hand, print_conf() is just used for debug, >>>> and user can always grab such information(/proc/mdstat and mdadm). >>>> >>>> There is no need to always enable this debug and try to fix misuse rcu >>>> protection for accessing rdev from 'conf', hence remove print_conf(). >>>> >>>> Signed-off-by: Yu Kuai <yukuai3@huawei.com> >>> >>> I wouldn't call these debug functions useless. There is probably some >>> users who use them for debugging (or even in some automations). >>> How hard is it to keep these functions? Can we just add some lockdep >>> to these functions to make sure they are called from safe places? >> >> Okay, I can keep these debug code, and since these code are >> dereferencing rdev from conf, and they need new syncronization: >> >> 1) dereference rdev from mddev->disks instead of conf, and use >> rdev->raid_disk >= 0 to judge if this rdev is in conf. There might >> be a race window that rdev can be removed from conf, however, I think >> this dones't matter. Or: >> >> 2) grab 'active_io' before print_conf(), to make sure rdev won't be >> removed from conf. > > I think for most of these cases, we can already do print_conf() > safely (holding mutex/lock), no? We can grab active_io when it is > really necessary.
Ok, I'll look into this, and send a v3 if there are no other corner cases.
Thanks, Kuai
> > Thanks, > Song > > . >
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