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locking/rwsem: Fix down_write_killable()

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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>
This commit is contained in:
Peter Zijlstra 2016-05-12 13:57:45 +02:00 committed by Ingo Molnar
parent 00fb16e26a
commit 04cafed7fc
1 changed files with 15 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

21
kernel/locking/rwsem-xadd.c
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@ -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