Re: [PATCH v8 08/13] libsas: libsas.force_hard_reset module parameter

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On Wed, Feb 29, 2012 at 1:55 PM, James Bottomley
<James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote:
> On Fri, 2012-02-10 at 00:45 -0800, Dan Williams wrote:
>> It is possible for a host to get "locked out" from talking to sata
>> devices in the domain if, for example, its sas address changes but the
>> expander topology has existing affiliations with the old address.  If
>> the system is booted userspace can write to
>> /sys/class/sas_phy/<phy-X>/hard_reset to clear the affiliation, however
>> if this condition exists for the root device the module parameter can be
>> used to promote all ata resets to hard resets.
>
> I don't quite understand this.  Are you saying we can't (or shouldn't)
> execute
>
> /sys/class/sas_phy/<phy-X>/hard_reset
>
> on the root device for some reason?

The case I ran into was accidentally changing the host sas address
between reboots.  If the sata device had been a root device then I
would not have been able boot the system.  But now that I think about
it, if Linux could not boot then neither could the pre-os
option-rom/efi driver.

>> After the system is booted this state can be cleared via
>> /sys/module/libsas/parameters/force_hard_reset
>
> I really don't think a module parameter for this is such a good idea ...
> it effectively promotes all soft resets to being hard ones, which can
> have a lot of unintended consequences.

Yes, it was only meant as a temporary "get out of a sticky situation"
option, but given the above pre-os-driver realization it is not even
useful for that case.  So I'm fine killing this patch.

--
Dan
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