From: Ming Lei <ming.lei@redhat.com>
To: Bart Van Assche <bvanassche@acm.org>
Cc: "Martin K . Petersen" <martin.petersen@oracle.com>,
linux-scsi@vger.kernel.org, Luis Chamberlain <mcgrof@kernel.org>,
Christoph Hellwig <hch@lst.de>, Hannes Reinecke <hare@suse.de>,
John Garry <john.garry@huawei.com>,
Mike Christie <michael.christie@oracle.com>,
Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-modules@vger.kernel.org, linux-kernel@vger.kernel.org,
"James E.J. Bottomley" <jejb@linux.ibm.com>,
Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH v5 6/7] module: Improve support for asynchronous module exit code
Date: Thu, 29 Sep 2022 09:10:27 +0800 [thread overview]
Message-ID: <YzTwgxX+WMuJyAJy@T590> (raw)
In-Reply-To: <2acc2220-65dc-4af5-ffd3-997f779d41c0@acm.org>
On Wed, Sep 28, 2022 at 12:27:07PM -0700, Bart Van Assche wrote:
> On 9/27/22 18:09, Ming Lei wrote:
> > On Wed, Sep 14, 2022 at 03:56:20PM -0700, Bart Van Assche wrote:
> > > Some kernel modules call device_del() from their module exit code and
> > > schedule asynchronous work from inside the .release callback without waiting
> > > until that callback has finished. As an example, many SCSI LLD drivers call
> >
> > It isn't only related with device, any kobject has such issue, or any
> > reference counter usage has similar potential risk, see previous discussion:
> >
> > https://lore.kernel.org/lkml/YsZm7lSXYAHT14ui@T590/
> >
> > IMO, it is one fundamental problem wrt. module vs. reference counting or
> > kobject uses at least, since the callback depends on module code
> > segment.
> >
> > > scsi_remove_host() from their module exit code. scsi_remove_host() may
> > > invoke scsi_device_dev_release_usercontext() asynchronously.
> > > scsi_device_dev_release_usercontext() uses the host template pointer and
> > > that pointer usually exists in static storage in the SCSI LLD. Support
> > > using the module reference count to keep the module around until
> > > asynchronous module exiting has completed by waiting in the delete_module()
> > > system call until the module reference count drops to zero.
> >
> > The issue can't be addressed by the normal mod->refcnt, since user need
> > to unload module when the device isn't used.
>
> Hi Ming,
>
> How about removing support for calling scsi_device_put() from atomic context
> as is done in the untested patch below?
That can't work.
The problem is that no existed mechanism can guarantee that kobject reference
drops to zero inside module_exit().
Thanks,
Ming
next prev parent reply other threads:[~2022-09-29 1:10 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20220914225621.415631-1-bvanassche@acm.org>
2022-09-14 22:56 ` [PATCH v5 6/7] module: Improve support for asynchronous module exit code Bart Van Assche
2022-09-20 17:13 ` Bart Van Assche
2022-09-28 0:02 ` Luis Chamberlain
2022-09-28 18:17 ` Bart Van Assche
2022-09-30 19:39 ` Luis Chamberlain
2022-10-03 23:56 ` Luis Chamberlain
2022-10-04 0:24 ` Bart Van Assche
2022-09-28 1:09 ` Ming Lei
2022-09-28 19:27 ` Bart Van Assche
2022-09-29 1:10 ` Ming Lei [this message]
2022-09-29 17:27 ` Bart Van Assche
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