Commit 04cafed7 authored May 12, 2016 by Peter Zijlstra Committed by Ingo Molnar May 15, 2016

locking/rwsem: Fix down_write_killable()



The new signal_pending exit path in __rwsem_down_write_failed_common()
was fingered as breaking his kernel by Tetsuo Handa.

Upon inspection it was found that there are two things wrong with it;

 - it forgets to remove WAITING_BIAS if it leaves the list empty, or
 - it forgets to wake further waiters that were blocked on the now
   removed waiter.

Especially the first issue causes new lock attempts to block and stall
indefinitely, as the code assumes that pending waiters mean there is
an owner that will wake when it releases the lock.

Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Tested-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Tested-by: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Chris Zankel <chris@zankel.net>
Cc: David S. Miller <davem@davemloft.net>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: Waiman Long <Waiman.Long@hpe.com>
Link: http://lkml.kernel.org/r/20160512115745.GP3192@twins.programming.kicks-ass.net


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 00fb16e2

kernel/locking/rwsem-xadd.c

+15 −6

Original line number	Diff line number	Diff line
		@@ -487,23 +487,32 @@ __rwsem_down_write_failed_common(struct rw_semaphore *sem, int state)

		/* Block until there are no active lockers. */
		do {
		if (signal_pending_state(state, current)) {
		raw_spin_lock_irq(&sem->wait_lock);
		ret = ERR_PTR(-EINTR);
		goto out;
		}
		if (signal_pending_state(state, current))
		goto out_nolock;

		schedule();
		set_current_state(state);
		} while ((count = sem->count) & RWSEM_ACTIVE_MASK);

		raw_spin_lock_irq(&sem->wait_lock);
		}
		out:
		__set_current_state(TASK_RUNNING);
		list_del(&waiter.list);
		raw_spin_unlock_irq(&sem->wait_lock);

		return ret;

		out_nolock:
		__set_current_state(TASK_RUNNING);
		raw_spin_lock_irq(&sem->wait_lock);
		list_del(&waiter.list);
		if (list_empty(&sem->wait_list))
		rwsem_atomic_update(-RWSEM_WAITING_BIAS, sem);
		else
		__rwsem_do_wake(sem, RWSEM_WAKE_ANY);
		raw_spin_unlock_irq(&sem->wait_lock);

		return ERR_PTR(-EINTR);
		}

		__visible struct rw_semaphore * __sched

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