[Xen-devel] [PATCH for-4.10] common/spinlock: Improve the output from check_lock() if it trips

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

If check_lock() triggers, a crash will occur.  Instead of simply identifying
"the irq context was different", indicate the expected and current irq
context.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Tim Deegan <tim@xxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>
CC: Julien Grall <julien.grall@xxxxxxx>

check_lock() only exists in debug builds, which makes this a low risk change
for 4.10.
---
 xen/common/spinlock.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/xen/common/spinlock.c b/xen/common/spinlock.c
index 44b07b7..8f2ba08 100644
--- a/xen/common/spinlock.c
+++ b/xen/common/spinlock.c
@@ -44,7 +44,13 @@ static void check_lock(struct lock_debug *debug)
     if ( unlikely(debug->irq_safe != irq_safe) )
     {
         int seen = cmpxchg(&debug->irq_safe, -1, irq_safe);
-        BUG_ON(seen == !irq_safe);
+
+        if ( seen == !irq_safe )
+        {
+            printk("CHECKLOCK FAILURE: prev irqsafe: %d, curr irqsafe %d\n",
+                   seen, irq_safe);
+            BUG();
+        }
     }
 }
 
-- 
2.1.4


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