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

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On Wed, 2012-02-29 at 15:22 -0800, Dan Williams wrote:
> 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.

Great, I'll drop it, thanks.

James


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