Re: [PATCH v2 1/4] scsi: sd: Let sd_shutdown() fail future I/O

[Bart Van Assche <bvanassche@acm.org>]

On 4/17/23 21:37, Ming Lei wrote:
> On Mon, Apr 17, 2023 at 04:06:53PM -0700, Bart Van Assche wrote:
>> System shutdown happens as follows (see e.g. the systemd source file
>> src/shutdown/shutdown.c):
>> * sync() is called.
>> * reboot(RB_AUTOBOOT/RB_HALT_SYSTEM/RB_POWER_OFF) is called.
>> * If the reboot() system call returns, log an error message.
>>
>> The reboot() system call causes the kernel to call kernel_restart(),
>> kernel_halt() or kernel_power_off(). Each of these functions calls
>> device_shutdown(). device_shutdown() calls sd_shutdown(). After
>> sd_shutdown() has been called the .shutdown() callback of the LLD
>> will be called. Hence, I/O submitted after sd_shutdown() will hang or
>> may even cause a kernel crash.
>>
>> Let sd_shutdown() fail future I/O such that LLD .shutdown() callbacks
>> can be simplified.
> 
> Hi Bart,
> 
> Last time you mentioned the current way may have kernel panic risk, but
> you never explain the panic, can you document the panic in commit log?

Hi Ming,

I removed the references to the risk of a kernel panic since I think 
that shutdown methods should not introduce that risk. From 
include/device/bus.h:

  * @shutdown:	Called at shut-down time to quiesce the device.

That comment says "quiesce the device". It does not say that it is 
allowed to crash the system if more I/O is submitted to the device.

Thanks,

Bart.