linux-kernel - Re: [PATCH v5] driver core: Add timeout for device shutdown

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Date: Thu, 13 Jun 2024 13:51:57 +0200
From: Daniel Lezcano <daniel.lezcano@...aro.org>
To: Greg KH <gregkh@...uxfoundation.org>,
 Soumya Khasnis <soumya.khasnis@...y.com>
Cc: rafael@...nel.org, linux-kernel@...r.kernel.org, festevam@...x.de,
 lee@...nel.org, benjamin.bara@...data.com, dmitry.osipenko@...labora.com,
 ldmldm05@...il.com, srinavasa.nagaraju@...y.com,
 Madhusudan.Bobbili@...y.com, shingo.takeuchi@...y.com,
 keita.aihara@...y.com, masaya.takahashi@...y.com
Subject: Re: [PATCH v5] driver core: Add timeout for device shutdown

On 13/06/2024 10:43, Greg KH wrote:
> On Thu, Jun 13, 2024 at 08:32:26AM +0000, Soumya Khasnis wrote:
>> The device shutdown callbacks invoked during shutdown/reboot
>> are prone to errors depending on the device state or mishandling
>> by one or more driver. In order to prevent a device hang in such
>> scenarios, we bail out after a timeout while dumping a meaningful
>> call trace of the shutdown callback to kernel logs, which blocks
>> the shutdown or reboot process.
> 
> Again, this is not a "device shutdown" timeout, it is a "the whole
> system has not shutdown this fast" timeout.
> 
> And in looking at my system, it doesn't shutdown in 10 seconds as it is
> madly flushing a ton of stuff out to the disks, and they are slow
> beasts.  So your 10 second default would cause me data loss on my
> workstation, not good!

Thanks for pointing this out. It is exactly what I was worried about ...

[ ... ]

> Isn't this just a bug in your drivers?  Why not fix them?  Or if you
> really have to have 10 seconds to shut down, use a watchdog timer that
> you trigger from userspace and stop petting once you want to shut down.
> Then, if it expires it will reset the machine, all of your policy
> decisions would have been done in userspace, no need to get the kernel
> involved at all.

+1


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