[dm-devel] [PATCH 1/2] dm-multipath: cleanup IO queueing after table load

[Benjamin Marzinski]

On Wed, Aug 13, 2014 at 10:46:15PM -0400, Mike Snitzer wrote:
> On Wed, Aug 13, 2014 at 2:53 PM, Benjamin Marzinski <bmarzins at redhat.com> wrote:
> > Commit e809917735ebf1b9a56c24e877ce0d320baee2ec changed the code in
> > multipath_busy that checked if a multipath device was initializing a path.
> > It returned busy if queue_io was set on the device. However queue_io is set
> > when the table is loaded, and as long as the device was busy, multipath_map
> > wouldn't run to clear it upon receiving requsts. multipath_ioctl and
> > reinstate_path were still able to clear queue_io. But if no paths were
> > reinstated and the multipath device received no ioctls after the table
> > reload, all requests to it would simply queue.
> >
> > This patch switches the multipath_busy code to check for a pending or in
> > progress path initialization, without using queue_io.  This means incoming
> > requests will allow multipath_map to initialize paths and clear queue_io.
> 
> This was already addressed with commit 7a7a3b45fe ("dm mpath: fix IO
> hang due to logic bug in multipath_busy").
> 
> > This patch also changes __choose_pgpath to make it clear queue_io if there
> > are no valid paths, since there are obviously no paths that can be
> > initialized.
> 
> Can you elaborate on why this is needed?  If it still is then it needs
> to be rebased.

For a while now, it's been possible to create a multipath table with no
devices.  With this patch set, it will be even easier to reload a
multipath device with no valid paths (since multipath now supports
reloading failed paths). In these scenarios, we still need to disable
queue_io, so that IOs to the device will not just back up.

-Ben

> 
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