Patch "locking/rwsem-spinlock: Fix EINTR branch in __down_write_common()" has been added to the 4.11-stable tree

This is a note to let you know that I've just added the patch titled

locking/rwsem-spinlock: Fix EINTR branch in __down_write_common()

to the 4.11-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
locking-rwsem-spinlock-fix-eintr-branch-in-__down_write_common.patch
and it can be found in the queue-4.11 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Kirill Tkhai <[email protected]>
Date: Fri, 16 Jun 2017 16:44:34 +0300
Subject: locking/rwsem-spinlock: Fix EINTR branch in __down_write_common()

From: Kirill Tkhai <[email protected]>

commit a0c4acd2c220376b4e9690e75782d0c0afdaab9f upstream.

If a writer could been woken up, the above branch

	if (sem->count == 0)
		break;

would have moved us to taking the sem. So, it's
not the time to wake a writer now, and only readers are allowed now. Thus, 0 must be passed to __rwsem_do_wake().

Next, __rwsem_do_wake() wakes readers unconditionally. But we mustn't do that if the sem is owned by writer in the moment. Otherwise, writer and reader own the sem the same time, which leads to memory corruption in callers.

rwsem-xadd.c does not need that, as:

1) the similar check is made lockless there,
2) in __rwsem_mark_wake::try_reader_grant we test,

that sem is not owned by writer.

---
 kernel/locking/rwsem-spinlock.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

@@ -231,8 +231,8 @@ int __sched __down_write_common(struct r
 
 out_nolock:
 	list_del(&waiter.list);
-	if (!list_empty(&sem->wait_list))
-		__rwsem_do_wake(sem, 1);
+	if (!list_empty(&sem->wait_list) && sem->count >= 0)
+		__rwsem_do_wake(sem, 0);
 	raw_spin_unlock_irqrestore(&sem->wait_lock, flags);
 
 	return -EINTR;

Patches currently in stable-queue which might be from [email protected] are

queue-4.11/locking-rwsem-spinlock-fix-eintr-branch-in-__down_write_common.patch