linux-kernel - [PATCH v5 08/18] fault_inject: Don't rely on "return value" from WRITE

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Date:   Mon, 11 May 2020 21:41:40 +0100
From:   Will Deacon <will@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     elver@...gle.com, tglx@...utronix.de, paulmck@...nel.org,
        mingo@...nel.org, peterz@...radead.org, will@...nel.org
Subject: [PATCH v5 08/18] fault_inject: Don't rely on "return value" from WRITE_ONCE()

It's a bit weird that WRITE_ONCE() evaluates to the value it stores and
it's also different to smp_store_release(), which can't be used this
way.

In preparation for preventing this in WRITE_ONCE(), change the fault
injection code to use a local variable instead.

Cc: Akinobu Mita <akinobu.mita@...il.com>
Signed-off-by: Will Deacon <will@...nel.org>
---
 lib/fault-inject.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/lib/fault-inject.c b/lib/fault-inject.c
index 8186ca84910b..ce12621b4275 100644
--- a/lib/fault-inject.c
+++ b/lib/fault-inject.c
@@ -106,7 +106,9 @@ bool should_fail(struct fault_attr *attr, ssize_t size)
 		unsigned int fail_nth = READ_ONCE(current->fail_nth);
 
 		if (fail_nth) {
-			if (!WRITE_ONCE(current->fail_nth, fail_nth - 1))
+			fail_nth--;
+			WRITE_ONCE(current->fail_nth, fail_nth);
+			if (!fail_nth)
 				goto fail;
 
 			return false;
-- 
2.26.2.645.ge9eca65c58-goog