From: "Theodore Y. Ts'o" <tytso@mit.edu>
To: Greg KH <gregkh@linuxfoundation.org>
Cc: Yufen Yu <yuyufen@huawei.com>,
axboe@kernel.dk, linux-block@vger.kernel.org,
linux-fsdevel@vger.kernel.org, tj@kernel.org, jack@suse.cz,
bvanassche@acm.org
Subject: Re: [PATCH v2 0/7] bdi: fix use-after-free for bdi device
Date: Wed, 4 Mar 2020 14:02:56 -0500 [thread overview]
Message-ID: <20200304190256.GB74069@mit.edu> (raw)
In-Reply-To: <20200304172907.GA1864710@kroah.com>
On Wed, Mar 04, 2020 at 06:29:07PM +0100, Greg KH wrote:
> The rule should be, "whenever you pass a pointer to a device off, the
> reference count is incremented". Somehow that is not happening here and
> RCU is not going to solve the issue really, it's only going to delay the
> problem from showing up until much later.
> ...
> The struct device refcount should be all that is needed, don't use RCU
> just to "delay freeing this object until some later time because someone
> else might have a pointer to id". That's ripe for disaster.
I agree that this is a better fix than trying to continue to paper
over the problem.
That being said, I also think it would be better if we could *also*
send a notification to the file system (or device mapper) when a block
device has disappeared, so we can set a flag in struct super
indicating, "this is an ex-device" so that we don't have to have
potentially hundreds of I/O errors clogging up the console and/or any
error notification ifrastructure we might want to add in the future,
as we attempt to send I/O to a device is not coming back. This would
allow us to short-circuit things like writeback, instead of letting
everything drain via pointless io_submits sending bios that will never
go anywhere useful.
- Ted
prev parent reply other threads:[~2020-03-04 19:03 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
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 [this message]
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