linux-kernel - [tip:locking/core] locking/rwsem: Fix down_write_killable() for CONFIG_RWSEM_GENERIC

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Date:   Thu, 16 Mar 2017 04:14:32 -0700
From:   tip-bot for Niklas Cassel <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
        hpa@...or.com, mingo@...nel.org, torvalds@...ux-foundation.org,
        mhocko@...e.com, tglx@...utronix.de, niklas.cassel@...s.com,
        akpm@...ux-foundation.org, niklass@...s.com,
        stable@...r.kernel.org, peterz@...radead.org
Subject: [tip:locking/core] locking/rwsem: Fix down_write_killable() for
 CONFIG_RWSEM_GENERIC_SPINLOCK=y

Commit-ID:  17fcbd590d0c3e35bd9646e2215f86586378bc42
Gitweb:     http://git.kernel.org/tip/17fcbd590d0c3e35bd9646e2215f86586378bc42
Author:     Niklas Cassel <niklas.cassel@...s.com>
AuthorDate: Sat, 25 Feb 2017 01:17:53 +0100
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Thu, 16 Mar 2017 09:28:30 +0100

locking/rwsem: Fix down_write_killable() for CONFIG_RWSEM_GENERIC_SPINLOCK=y

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@...s.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: <mhocko@...e.com>
Cc: <stable@...r.kernel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Niklas Cassel <niklass@...s.com>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.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@...nel.org>
---
 kernel/locking/rwsem-spinlock.c | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/kernel/locking/rwsem-spinlock.c b/kernel/locking/rwsem-spinlock.c
index 7bc24d4..c65f798 100644
--- a/kernel/locking/rwsem-spinlock.c
+++ b/kernel/locking/rwsem-spinlock.c
@@ -213,10 +213,9 @@ int __sched __down_write_common(struct rw_semaphore *sem, int state)
 		 */
 		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_current_state(state);
 		raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
 		schedule();
@@ -224,12 +223,19 @@ int __sched __down_write_common(struct rw_semaphore *sem, int state)
 	}
 	/* 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)