Re: [PATCH 4.4 48/76] libceph: force GFP_NOIO for socket allocations

[Michal Hocko <mhocko@kernel.org>]

On Wed 29-03-17 12:41:26, Michal Hocko wrote:
[...]
> > ceph_con_workfn
> >   mutex_lock(&con->mutex)  # ceph_connection::mutex
> >   try_write
> >     ceph_tcp_connect
> >       sock_create_kern
> >         GFP_KERNEL allocation
> >           allocator recurses into XFS, more I/O is issued

One more note. So what happens if this is a GFP_NOIO request which
cannot make any progress? Your IO thread is blocked on con->mutex
as you write below but the above thread cannot proceed as well. So I am
_really_ not sure this acutally helps.

[...]
> > 
> > rbd_queue_workfn
> >   ceph_osdc_start_request
> >     mutex_lock(&osdc->request_mutex);
> >     ceph_con_send
> >       mutex_lock(&con->mutex)  # deadlock

-- 
Michal Hocko
SUSE Labs