Hello, Peter. On Thu, Dec 14, 2017 at 09:20:42PM +0100, Peter Zijlstra wrote: > But now that I look at this again, TJ, why can't the below happen? > > write_seqlock_begin(); > blk_mq_rq_update_state(rq, IN_FLIGHT); > blk_add_timer(rq); > <timer-irq> > read_seqcount_begin() > while (seq & 1) > cpurelax(); > // life-lock > </timer-irq> > write_seqlock_end(); Ah, you're right. For both gstate_seq and aborted_gstate_sync, we can push all synchronization to the timeout side - ie. gstate_seq read can yield, pause or synchronize_rcu and hte aborted_gstate_sync can disable irq around update. Thanks. -- tejun
