Re: [PATCH 03/11] locking, rwsem: introduce basis for down_write_killable
From: Peter Zijlstra <peterz@infradead.org>
Date: 2016-03-30 13:26:08
Also in:
linux-arch, linux-s390, linux-sh, lkml, sparclinux
On Mon, Feb 29, 2016 at 01:58:17PM +0100, Michal Hocko wrote:
quoted hunk ↗ jump to hunk
@@ -215,16 +216,34 @@ void __sched __down_write(struct rw_semaphore *sem) */ if (sem->count == 0) break; - set_task_state(tsk, TASK_UNINTERRUPTIBLE); + set_task_state(tsk, state); raw_spin_unlock_irqrestore(&sem->wait_lock, flags); schedule(); + if (signal_pending_state(state, current)) { + ret = -EINTR; + raw_spin_lock_irqsave(&sem->wait_lock, flags); + goto out; + } raw_spin_lock_irqsave(&sem->wait_lock, flags); } /* got the lock */ sem->count = -1;
quoted hunk ↗ jump to hunk
@@ -487,20 +488,38 @@ struct rw_semaphore __sched *rwsem_down_write_failed(struct rw_semaphore *sem) /* Block until there are no active lockers. */ do { schedule(); - set_current_state(TASK_UNINTERRUPTIBLE); + if (signal_pending_state(state, current)) { + raw_spin_lock_irq(&sem->wait_lock); + ret = ERR_PTR(-EINTR); + goto out; + } + set_current_state(state); } while ((count = sem->count) & RWSEM_ACTIVE_MASK); raw_spin_lock_irq(&sem->wait_lock); } __set_current_state(TASK_RUNNING);
Why is the signal_pending_state() test _after_ the call to schedule() and before the 'trylock'. __mutex_lock_common() has it before the call to schedule and after the 'trylock'. The difference is that rwsem will now respond to the KILL and return -EINTR even if the lock is available, whereas mutex will acquire it and ignore the signal (for a little while longer). Neither is wrong per se, but I feel all the locking primitives should behave in a consistent manner in this regard.