[PATCH 07/10] fault injection: down_trylock() fault injection

[Vegard Nossum <vegard.nossum@oracle.com>]

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
---
 kernel/locking/semaphore.c | 26 ++++++++++++++++++++++++++
 lib/Kconfig.debug          |  6 ++++++
 2 files changed, 32 insertions(+)

diff --git a/kernel/locking/semaphore.c b/kernel/locking/semaphore.c
index b8120ab..367bae3 100644
--- a/kernel/locking/semaphore.c
+++ b/kernel/locking/semaphore.c
@@ -25,6 +25,7 @@
  * semaphore.  If it's zero, there may be tasks waiting on the wait_list.
  */
 
+#include <linux/fault-inject.h>
 #include <linux/compiler.h>
 #include <linux/kernel.h>
 #include <linux/export.h>
@@ -114,6 +115,28 @@ int down_killable(struct semaphore *sem)
 }
 EXPORT_SYMBOL(down_killable);
 
+#ifdef CONFIG_FAIL_SEMAPHORE
+DECLARE_FAULT_ATTR(fail_semaphore);
+
+static int __init fail_semaphore_debugfs(void)
+{
+	struct dentry *dir = fault_create_debugfs_attr("fail_semaphore",
+		NULL, &fail_semaphore);
+	return PTR_ERR_OR_ZERO(dir);
+}
+late_initcall(fail_semaphore_debugfs);
+
+static inline bool should_fail_semaphore(struct semaphore *sem)
+{
+	return should_fail(&fail_semaphore, 1);
+}
+#else
+static inline bool should_fail_semaphore(struct semaphore *sem)
+{
+	return false;
+}
+#endif
+
 /**
  * down_trylock - try to acquire the semaphore, without waiting
  * @sem: the semaphore to be acquired
@@ -132,6 +155,9 @@ int down_trylock(struct semaphore *sem)
 	unsigned long flags;
 	int count;
 
+	if (should_fail_semaphore(sem))
+		return 1;
+
 	raw_spin_lock_irqsave(&sem->lock, flags);
 	count = sem->count - 1;
 	if (likely(count >= 0))
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 12ad8eb..1e134de 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1669,6 +1669,12 @@ config FAIL_RT_MUTEX
 	help
 	  Provide fault-injection capability for rt_mutex_trylock().
 
+config FAIL_SEMAPHORE
+	bool "Fault-injection capability for semaphores"
+	depends on FAULT_INJECTION
+	help
+	  Provide fault-injection capability for down_trylock().
+
 config FAULT_INJECTION_DEBUG_FS
 	bool "Debugfs entries for fault-injection capabilities"
 	depends on FAULT_INJECTION && SYSFS && DEBUG_FS
-- 
2.10.0.479.g221bd91