On Wed 29-03-17 13:10:01, Ilya Dryomov wrote: > On Wed, Mar 29, 2017 at 12:55 PM, Michal Hocko <mhocko@xxxxxxxxxx> wrote: > > 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. > > This is not the only I/O worker. A ceph cluster typically consists of > at least a few OSDs and can be as large as thousands of OSDs. This is > the reason we are calling sock_create_kern() on the writeback path in > the first place: pre-opening thousands of sockets isn't feasible. Sorry for being dense here but what actually guarantees the forward progress? My current understanding is that the deadlock is caused by con->mutext being held while the allocation cannot make a forward progress. I can imagine this would be possible if the other io flushers depend on this lock. But then NOIO vs. KERNEL allocation doesn't make much difference. What am I missing? -- Michal Hocko SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
