From: Xu Yilun <yilun.xu@linux.intel.com>
To: Marco Pagani <marpagan@redhat.com>
Cc: Moritz Fischer <mdf@kernel.org>, Wu Hao <hao.wu@intel.com>,
Xu Yilun <yilun.xu@intel.com>, Tom Rix <trix@redhat.com>,
Jonathan Corbet <corbet@lwn.net>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Alan Tull <atull@opensource.altera.com>,
linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
linux-fpga@vger.kernel.org
Subject: Re: [RFC PATCH v5 1/1] fpga: add an owner and use it to take the low-level module's refcount
Date: Fri, 1 Mar 2024 23:12:42 +0800 [thread overview]
Message-ID: <ZeHwatupHVmC2N2+@yilunxu-OptiPlex-7050> (raw)
In-Reply-To: <0c885ff2-44bc-4158-b5dd-3d7513cb2857@redhat.com>
On Thu, Feb 29, 2024 at 11:37:10AM +0100, Marco Pagani wrote:
>
> On 2024-02-28 08:10, Xu Yilun wrote:
> > On Tue, Feb 27, 2024 at 12:49:06PM +0100, Marco Pagani wrote:
> >>
> >>
> >> On 2024-02-21 15:37, Xu Yilun wrote:
> >>> On Tue, Feb 20, 2024 at 12:11:26PM +0100, Marco Pagani wrote:
> >>>>
> >>>>
> >>>> On 2024-02-18 11:05, Xu Yilun wrote:
> >>>>> On Mon, Feb 05, 2024 at 06:47:34PM +0100, Marco Pagani wrote:
> >>>>>>
> >>>>>>
> >>>>>> On 2024-02-04 06:15, Xu Yilun wrote:
> >>>>>>> On Fri, Feb 02, 2024 at 06:44:01PM +0100, Marco Pagani wrote:
> >>>>>>>>
> >>>>>>>>
> >>>>>>>> On 2024-01-30 05:31, Xu Yilun wrote:
> >>>>>>>>>> +#define fpga_mgr_register_full(parent, info) \
> >>>>>>>>>> + __fpga_mgr_register_full(parent, info, THIS_MODULE)
> >>>>>>>>>> struct fpga_manager *
> >>>>>>>>>> -fpga_mgr_register_full(struct device *parent, const struct fpga_manager_info *info);
> >>>>>>>>>> +__fpga_mgr_register_full(struct device *parent, const struct fpga_manager_info *info,
> >>>>>>>>>> + struct module *owner);
> >>>>>>>>>>
> >>>>>>>>>> +#define fpga_mgr_register(parent, name, mops, priv) \
> >>>>>>>>>> + __fpga_mgr_register(parent, name, mops, priv, THIS_MODULE)
> >>>>>>>>>> struct fpga_manager *
> >>>>>>>>>> -fpga_mgr_register(struct device *parent, const char *name,
> >>>>>>>>>> - const struct fpga_manager_ops *mops, void *priv);
> >>>>>>>>>> +__fpga_mgr_register(struct device *parent, const char *name,
> >>>>>>>>>> + const struct fpga_manager_ops *mops, void *priv, struct module *owner);
> >>>>>>>>>> +
> >>>>>>>>>> void fpga_mgr_unregister(struct fpga_manager *mgr);
> >>>>>>>>>>
> >>>>>>>>>> +#define devm_fpga_mgr_register_full(parent, info) \
> >>>>>>>>>> + __devm_fpga_mgr_register_full(parent, info, THIS_MODULE)
> >>>>>>>>>> struct fpga_manager *
> >>>>>>>>>> -devm_fpga_mgr_register_full(struct device *parent, const struct fpga_manager_info *info);
> >>>>>>>>>> +__devm_fpga_mgr_register_full(struct device *parent, const struct fpga_manager_info *info,
> >>>>>>>>>> + struct module *owner);
> >>>>>>>>>
> >>>>>>>>> Add a line here. I can do it myself if you agree.
> >>>>>>>>
> >>>>>>>> Sure, that is fine by me. I also spotted a typo in the commit log body
> >>>>>>>> (in taken -> is taken). Do you want me to send a v6, or do you prefer
> >>>>>>>> to fix that in place?
> >>>>>>>
> >>>>>>> No need, I can fix it.
> >>>>>>>
> >>>>>>>>
> >>>>>>>>>
> >>>>>>>>> There is still a RFC prefix for this patch. Are you ready to get it merged?
> >>>>>>>>> If yes, Acked-by: Xu Yilun <yilun.xu@intel.com>
> >>>>>>>>
> >>>>>>>> I'm ready for the patch to be merged. However, I recently sent an RFC
> >>>>>>>> to propose a safer implementation of try_module_get() that would
> >>>>>>>> simplify the code and may also benefit other subsystems. What do you
> >>>>>>>> think?
> >>>>>>>>
> >>>>>>>> https://lore.kernel.org/linux-modules/20240130193614.49772-1-marpagan@redhat.com/
> >>>>>>>
> >>>>>>> I suggest take your fix to linux-fpga/for-next now. If your try_module_get()
> >>>>>>> proposal is applied before the end of this cycle, we could re-evaluate
> >>>>>>> this patch.
> >>>>>>
> >>>>>> That's fine by me.
> >>>>>
> >>>>> Sorry, I still found issues about this solution.
> >>>>>
> >>>>> void fpga_mgr_unregister(struct fpga_manager *mgr)
> >>>>> {
> >>>>> dev_info(&mgr->dev, "%s %s\n", __func__, mgr->name);
> >>>>>
> >>>>> /*
> >>>>> * If the low level driver provides a method for putting fpga into
> >>>>> * a desired state upon unregister, do it.
> >>>>> */
> >>>>> fpga_mgr_fpga_remove(mgr);
> >>>>>
> >>>>> mutex_lock(&mgr->mops_mutex);
> >>>>>
> >>>>> mgr->mops = NULL;
> >>>>>
> >>>>> mutex_unlock(&mgr->mops_mutex);
> >>>>>
> >>>>> device_unregister(&mgr->dev);
> >>>>> }
> >>>>>
> >>>>> Note that fpga_mgr_unregister() doesn't have to be called in module_exit().
> >>>>> So if we do fpga_mgr_get() then fpga_mgr_unregister(), We finally had a
> >>>>> fpga_manager dev without mops, this is not what the user want and cause
> >>>>> problem when using this fpga_manager dev for other FPGA APIs.
> >>>>
> >>>> How about moving mgr->mops = NULL from fpga_mgr_unregister() to
> >>>> class->dev_release()? In that way, mops will be set to NULL only when the
> >>>> manager dev refcount reaches 0.
> >>>
> >>> I'm afraid it doesn't help. The lifecycle of the module and the fpga
> >>> mgr dev is different.
> >>>
> >>> We use mops = NULL to indicate module has been freed or will be freed in no
> >>> time. On the other hand mops != NULL means module is still there, so
> >>> that try_module_get() could be safely called. It is possible someone
> >>> has got fpga mgr dev but not the module yet, at that time the module is
> >>> unloaded, then try_module_get() triggers crash.
> >>>
> >>>>
> >>>> If fpga_mgr_unregister() is called from module_exit(), we are sure that nobody
> >>>> got the manager dev earlier using fpga_mgr_get(), or it would have bumped up
> >>>
> >>> No, someone may get the manager dev but not the module yet, and been
> >>> scheduled out.
> >>>
> >>
> >> You are right. Overall, it's a bad idea. How about then using an additional
> >> bool flag instead of "overloading" the mops pointer? Something like:
> >>
> >> get:
> >> if (!mgr->owner_valid || !try_module_get(mgr->mops_owner))
> >>
> >> remove:
> >> mgr->owner_valid = false;
> >
> > I'm not quite sure which function is actually mentioned by "remove". I
> > assume it should be fpga_mgr_unregister().
>
> Yes, I was referring to fpga_mgr_unregister().
>
> > IIUC this flag means no more reference to fpga mgr, but existing
> > references are still valid.
>
> Yes.
>
> >
> > It works for me. But the name of this flag could be reconsidered to
> > avoid misunderstanding. The owner is still valid (we still need to put
> > the owner) but allows no more reference. Maybe "owner_inactive"?
>
> Right, owner_valid might be misleading. How about removing any
> reference to the owner module and name the flag unreg?
the full name "unregistered" is better.
>
> __fpga_mgr_get:
> if (mgr->unreg || !try_module_get(mgr->mops_owner))
> mgr = ERR_PTR(-ENODEV);
>
> fpga_mgr_unregister:
> mgr->unreg = true;
>
> > I still wanna this owner reference change been splitted, so that
> > we could simply revert it when the try_module_get_safe() got accepted.
>
> I guess it may take some time to have try_module_get_safe() accepted.
> What do you prefer to do with the bridge and the region in the
> meantime?
This issue could happen in little chance. I actually don't have much
preference, either way is good to me.
Thanks,
Yilun
>
> Thanks,
> Marco
>
next prev parent reply other threads:[~2024-03-01 15:16 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-11 16:02 [RFC PATCH v5 0/1] fpga: improve protection against low-level control module unloading Marco Pagani
2024-01-11 16:02 ` [RFC PATCH v5 1/1] fpga: add an owner and use it to take the low-level module's refcount Marco Pagani
2024-01-30 4:31 ` Xu Yilun
2024-02-02 17:44 ` Marco Pagani
2024-02-04 5:15 ` Xu Yilun
2024-02-05 17:47 ` Marco Pagani
2024-02-18 10:05 ` Xu Yilun
2024-02-20 11:11 ` Marco Pagani
2024-02-21 14:37 ` Xu Yilun
2024-02-27 11:49 ` Marco Pagani
2024-02-28 7:10 ` Xu Yilun
2024-02-29 10:37 ` Marco Pagani
2024-03-01 15:12 ` Xu Yilun [this message]
2024-03-01 16:29 ` Marco Pagani
2024-03-04 11:51 ` Marco Pagani
2024-03-04 13:49 ` Xu Yilun
2024-03-04 22:26 ` Marco Pagani
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