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Subject[PATCH 4.9 92/93] locking/rwsem: Fix down_write_killable() for CONFIG_RWSEM_GENERIC_SPINLOCK=y
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Niklas Cassel <niklas.cassel@axis.com>

commit 17fcbd590d0c3e35bd9646e2215f86586378bc42 upstream.

We hang if SIGKILL has been sent, but the task is stuck in down_read()
(after do_exit()), even though no task is doing down_write() on the
rwsem in question:

INFO: task libupnp:21868 blocked for more than 120 seconds.
libupnp D 0 21868 1 0x08100008
...
Call Trace:
__schedule()
schedule()
__down_read()
do_exit()
do_group_exit()
__wake_up_parent()

This bug has already been fixed for CONFIG_RWSEM_XCHGADD_ALGORITHM=y in
the following commit:

04cafed7fc19 ("locking/rwsem: Fix down_write_killable()")

... however, this bug also exists for CONFIG_RWSEM_GENERIC_SPINLOCK=y.

Signed-off-by: Niklas Cassel <niklas.cassel@axis.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <mhocko@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Niklas Cassel <niklass@axis.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: d47996082f52 ("locking/rwsem: Introduce basis for down_write_killable()")
Link: http://lkml.kernel.org/r/1487981873-12649-1-git-send-email-niklass@axis.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
kernel/locking/rwsem-spinlock.c | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)

--- a/kernel/locking/rwsem-spinlock.c
+++ b/kernel/locking/rwsem-spinlock.c
@@ -216,10 +216,8 @@ int __sched __down_write_common(struct r
*/
if (sem->count == 0)
break;
- if (signal_pending_state(state, current)) {
- ret = -EINTR;
- goto out;
- }
+ if (signal_pending_state(state, current))
+ goto out_nolock;
set_task_state(tsk, state);
raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
schedule();
@@ -227,12 +225,19 @@ int __sched __down_write_common(struct r
}
/* got the lock */
sem->count = -1;
-out:
list_del(&waiter.list);

raw_spin_unlock_irqrestore(&sem->wait_lock, flags);

return ret;
+
+out_nolock:
+ list_del(&waiter.list);
+ if (!list_empty(&sem->wait_list))
+ __rwsem_do_wake(sem, 1);
+ raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
+
+ return -EINTR;
}

void __sched __down_write(struct rw_semaphore *sem)

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