[dm-devel] dm-mpath: do not change SCSI device handler
Mike Snitzer
snitzer at redhat.com
Thu Apr 4 13:16:31 UTC 2013
On Thu, Apr 04 2013 at 8:55am -0400,
Mikulas Patocka <mpatocka at redhat.com> wrote:
>
>
> On Thu, 4 Apr 2013, Mike Snitzer wrote:
>
> > I'll take a look at fixing this by deferring the scsi_dh switch until
> > resume. This fix would assume multipath-tools is _not_ doing a noflush
> > suspend/resume when it is switching the scsi_dh.
> >
> > Mike
>
> This won't work because scsi_dh_attach allocates memory and you can't
> allocate memory when something is suspended.
Ah yeah, scsi_dh->attach allocates memory for scsi_dh_data. But
couldn't those scsi_dh_* attach allocations be switched from GFP_KERNEL
to GFP_NOIO?
> If we want to make it possible to change device handler, we need to add a
> counter to "struct scsi_dh_data", increment the counter when the device
> handler issues some request, decrement the counter when it finishes the
> request (it may be tricky because you can't decrement it from the device
> handler module because the module may be unloaded as soon as you decrement
> it). Then, you wait until the counter is zero and detach the handler.
Noted, but I haven't given up hope on just deferring the scsi_dh switch
quite yet.
Mike
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