From: Jan Beulich <jbeulich@suse.com>
Date: Tue, 29 Mar 2016 15:16:23 +0000 (+0200)
Subject: spinlock: improve spin_is_locked() for recursive locks
X-Git-Tag: archive/raspbian/4.8.0-1+rpi1~1^2~1477
X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=bb9373a802f5413880dec591a57292a877178d17;p=xen.git

spinlock: improve spin_is_locked() for recursive locks

Recursive locks know their current owner, and since we use the function
solely to determine whether a particular lock is being held by the
current CPU (which so far has been an imprecise check), make actually
check the owner for recusrively acquired locks.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Dario Faggioli <dario.faggioli@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Quan Xu <quan.xu@intel.com>
Acked-by: Tim Deegan <tim@xen.org>
---

diff --git a/xen/common/spinlock.c b/xen/common/spinlock.c
index a43fa84f5b..b377bb907b 100644
--- a/xen/common/spinlock.c
+++ b/xen/common/spinlock.c
@@ -188,7 +188,15 @@ void _spin_unlock_irqrestore(spinlock_t *lock, unsigned long flags)
 int _spin_is_locked(spinlock_t *lock)
 {
     check_lock(&lock->debug);
-    return lock->tickets.head != lock->tickets.tail;
+
+    /*
+     * Recursive locks may be locked by another CPU, yet we return
+     * "false" here, making this function suitable only for use in
+     * ASSERT()s and alike.
+     */
+    return lock->recurse_cpu == SPINLOCK_NO_CPU
+           ? lock->tickets.head != lock->tickets.tail
+           : lock->recurse_cpu == smp_processor_id();
 }
 
 int _spin_trylock(spinlock_t *lock)