Re: Freeze after disabling write cache with hdparm -W0 /dev/sda

[Tejun Heo <htejun@gmail.com>]

Simon Farnsworth wrote:
> Tejun Heo wrote:
>> Simon Farnsworth wrote:
>>> Tejun Heo wrote:
>>>> Simon Farnsworth wrote:
>>>>> Just a thought; is it possible to trigger libata EH from userspace? If
>>>>> so, we could write a small utility to disable write cache, then force EH
>>>>> to detect the change.
>>>> That's automatically done.  libata snoops cache on/off and triggers
>>>> revalidation but you can request manual rescan by echoing "- - -" to
>>>> /sys/class/scsi_host/hostX/scan.
>>>>
>>> Would it be worth changing our code to do "hdparm -W1 /dev/sda && hdparm
>>> -W0 /dev/sda", or would this not show anything. The lack of revalidation
>>> on some drives is what's worrying me a little here.
>> Revalidation happens after cache property is changed successfully.  What
>> happens if you request manual rescan while the drive is not repsponding?
>>
> The 30 second freeze happens when we request manual rescan. We do
> revalidate once the freeze is over, though; dmesg follows:

Can you post dmesg with printk timestamps turned on?

-- 
tejun