[PATCH 04/10] fault injection: prevent recursive fault injection

[Vegard Nossum]

If something we call in the fail_dump() code path tries to acquire a
resource that might fail (due to fault injection), then we should not
try to recurse back into the fault injection code.

I've seen this happen with the console semaphore in the upcoming
semaphore trylock fault injection code.

Signed-off-by: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
---
 lib/fault-inject.c | 34 ++++++++++++++++++++++++++++------
 1 file changed, 28 insertions(+), 6 deletions(-)

diff --git a/lib/fault-inject.c b/lib/fault-inject.c
index 6a823a5..adba7c9 100644
--- a/lib/fault-inject.c
+++ b/lib/fault-inject.c
@@ -100,6 +100,33 @@ static inline bool fail_stacktrace(struct fault_attr *attr)
 
 #endif /* CONFIG_FAULT_INJECTION_STACKTRACE_FILTER */
 
+static DEFINE_PER_CPU(int, fault_active);
+
+static bool __fail(struct fault_attr *attr)
+{
+	bool ret = false;
+
+	/*
+	 * Prevent recursive fault injection (this could happen if for
+	 * example printing the fault would itself run some code that
+	 * could fail)
+	 */
+	preempt_disable();
+	if (unlikely(__this_cpu_inc_return(fault_active) != 1))
+		goto out;
+
+	ret = true;
+	fail_dump(attr);
+
+	if (atomic_read(&attr->times) != -1)
+		atomic_dec_not_zero(&attr->times);
+
+out:
+	__this_cpu_dec(fault_active);
+	preempt_enable();
+	return ret;
+}
+
 /*
  * This code is stolen from failmalloc-1.0
  * http://www.nongnu.org/failmalloc/
@@ -134,12 +161,7 @@ bool should_fail(struct fault_attr *attr, ssize_t size)
 	if (!fail_stacktrace(attr))
 		return false;
 
-	fail_dump(attr);
-
-	if (atomic_read(&attr->times) != -1)
-		atomic_dec_not_zero(&attr->times);
-
-	return true;
+	return __fail(attr);
 }
 EXPORT_SYMBOL_GPL(should_fail);
 
-- 
1.9.1