From: clefru <clemens@endorphin.org>
Date: Thu, 19 Jan 2017 22:41:38 +0000 (+0100)
Subject: Reimplement rt_mutex_owner to fix build with DEBUG & PREEMPT_RT_FULL
X-Git-Tag: zfs-0.8.0-rc1~152^2~59
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=2d4d81c485bd5ed3ccaf1580c4efdc0ecdbc52ee;p=zfs

Reimplement rt_mutex_owner to fix build with DEBUG & PREEMPT_RT_FULL

rt_mutex_owner is internal to kernel/locking/rtmutex_common.h and
inaccessible for SPL via the public kernel headers. The way of
accessing the owner has been stable since at least 3.13 ([1], [2]),
which is masking the lowest bit in the owner pointer in rt_mutex. We
do the same.

[1] http://lxr.free-electrons.com/source/kernel/locking/rtmutex_common.h?v=3.13#L99
[2] http://lxr.free-electrons.com/source/kernel/locking/rtmutex_common.h?v=4.9#L78

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Clemens Fruhwirth <clemens@endorphin.org>
Closes #593
---

diff --git a/module/spl/spl-rwlock.c b/module/spl/spl-rwlock.c
index 9e96c4f27..d99ef4f92 100644
--- a/module/spl/spl-rwlock.c
+++ b/module/spl/spl-rwlock.c
@@ -35,11 +35,15 @@
 #if defined(CONFIG_PREEMPT_RT_FULL)
 
 #include <linux/rtmutex.h>
+#define	RT_MUTEX_OWNER_MASKALL	1UL
 
 static int
 __rwsem_tryupgrade(struct rw_semaphore *rwsem)
 {
-	ASSERT(rt_mutex_owner(&rwsem->lock) == current);
+
+	ASSERT((struct task_struct *)
+	    ((unsigned long)rwsem->lock.owner & ~RT_MUTEX_OWNER_MASKALL) ==
+	    current);
 
 	/*
 	 * Under the realtime patch series, rwsem is implemented as a