From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Tejun Heo <tj@kernel.org>
Cc: Yufen Yu <yuyufen@huawei.com>,
axboe@kernel.dk, linux-block@vger.kernel.org,
linux-fsdevel@vger.kernel.org, jack@suse.cz, bvanassche@acm.org,
tytso@mit.edu
Subject: Re: [PATCH v2 3/7] bdi: protect device lifetime with RCU
Date: Wed, 4 Mar 2020 21:05:59 +0100 [thread overview]
Message-ID: <20200304200559.GA1906005@kroah.com> (raw)
In-Reply-To: <20200304185056.GM189690@mtj.thefacebook.com>
On Wed, Mar 04, 2020 at 01:50:56PM -0500, Tejun Heo wrote:
> Hello,
>
> On Wed, Mar 04, 2020 at 06:22:21PM +0100, Greg Kroah-Hartman wrote:
> > Ugh, I was dreading the fact that this day might sometime come...
> >
> > In theory, the reference counting for struct device shouldn't need to
> > use rcu at all, right? what is driving the need to use rcu for
>
> Lifetime rules in block layer are kinda nebulous. Some of it comes
> from the fact that some objects are reused. Instead of the usual,
> create-use-release, they get repurposed to be associated with
> something else. When looking at such an object from some paths, we
> don't necessarily have ownership of all of the members.
That's horrid, it's not like block devices are on some "fast path" for
tear-down, we should do it correctly.
> > backing_device_info? Are these being destroyed/used so often that rcu
> > really is the best solution and the existing reference counting doesn't
> > work properly?
>
> It's more that there are entry points which can only ensure that just
> the top level object is valid and the member objects might be going or
> coming as we're looking at it.
That's not ok, a "member object" can only be valid if you have a
reference to it. If you remove the object, you then drop the reference,
shouldn't that be the correct thing to do?
thanks,
greg k-h
next prev parent reply other threads:[~2020-03-04 20:06 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-26 11:18 [PATCH v2 0/7] bdi: fix use-after-free for bdi device Yufen Yu
2020-02-26 11:18 ` [PATCH v2 1/7] blk-wbt: use bdi_dev_name() to get device name Yufen Yu
2020-02-26 11:18 ` [PATCH v2 2/7] fs/ceph: " Yufen Yu
2020-02-26 11:18 ` [PATCH v2 3/7] bdi: protect device lifetime with RCU Yufen Yu
2020-03-04 17:05 ` Tejun Heo
2020-03-04 17:22 ` Greg Kroah-Hartman
2020-03-04 17:23 ` Greg Kroah-Hartman
2020-03-04 18:50 ` Tejun Heo
2020-03-04 19:10 ` Theodore Y. Ts'o
2020-03-04 19:15 ` Tejun Heo
2020-03-04 20:05 ` Greg Kroah-Hartman [this message]
2020-03-05 1:22 ` Tejun Heo
2020-03-06 16:25 ` Greg Kroah-Hartman
2020-03-07 9:13 ` Yufen Yu
2020-02-26 11:18 ` [PATCH v2 4/7] bdi: create a new function bdi_get_dev_name() Yufen Yu
2020-02-26 11:18 ` [PATCH v2 5/7] bfq: fix potential kernel crash when print dev err info Yufen Yu
2020-02-26 11:18 ` [PATCH v2 6/7] memcg: fix crash in wb_workfn when bdi unregister Yufen Yu
2020-02-26 11:18 ` [PATCH v2 7/7] blk-wbt: replace bdi_dev_name() with bdi_get_dev_name() Yufen Yu
2020-03-04 17:29 ` [PATCH v2 0/7] bdi: fix use-after-free for bdi device Greg KH
2020-03-04 18:57 ` Tejun Heo
2020-03-04 20:07 ` Greg KH
2020-03-04 19:02 ` Theodore Y. Ts'o
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200304200559.GA1906005@kroah.com \
--to=gregkh@linuxfoundation.org \
--cc=axboe@kernel.dk \
--cc=bvanassche@acm.org \
--cc=jack@suse.cz \
--cc=linux-block@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=tj@kernel.org \
--cc=tytso@mit.edu \
--cc=yuyufen@huawei.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.