2020-03-28 16:45:00

by George Spelvin

[permalink] [raw]
Subject: [RFC PATCH v1 02/50] lib/fault-inject.c: Fix off-by-one error in probability

This is the combination of two fixes. First, use prandom_u32_max() for
efficiency:
- if (attr->probability <= prandom_u32() % 100)
+ if (attr->probability <= prandom_u32_max(100))
return false

And then a bug-fix:
- if (attr->probability <= prandom_u32_max(100))
+ if (attr->probability < prandom_u32_max(100))
return false

Before, probability = 1 would succeed 2% of the time and 99 would
succeed 100% of the time. (0% was caught by an earlier test.)

Signed-off-by: George Spelvin <[email protected]>
Cc: Akinobu Mita <[email protected]>
Cc: Anton Blanchard <[email protected]>
---
lib/fault-inject.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/fault-inject.c b/lib/fault-inject.c
index 8186ca84910bc..e20151fa5515e 100644
--- a/lib/fault-inject.c
+++ b/lib/fault-inject.c
@@ -134,7 +134,7 @@ bool should_fail(struct fault_attr *attr, ssize_t size)
return false;
}

- if (attr->probability <= prandom_u32() % 100)
+ if (attr->probability < prandom_u32_max(100))
return false;

if (!fail_stacktrace(attr))
--
2.26.0