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From:   Will Deacon <will@kernel.org>
To:     linux-kernel@vger.kernel.org
Cc:     linux-arch@vger.kernel.org, kernel-team@android.com,
        Will Deacon <will@kernel.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Peter Zijlstra <peterz@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Segher Boessenkool <segher@kernel.crashing.org>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Luc Van Oostenryck <luc.vanoostenryck@gmail.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Akinobu Mita <akinobu.mita@gmail.com>
Subject: [RFC PATCH 3/8] fault_inject: Don't rely on "return value" from WRITE_ONCE()
Date:   Fri, 10 Jan 2020 16:56:31 +0000
Message-Id: <20200110165636.28035-4-will@kernel.org>
In-Reply-To: <20200110165636.28035-1-will@kernel.org>
References: <20200110165636.28035-1-will@kernel.org>
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It's a bit weird that WRITE_ONCE() evaluates to the value it stores and
it's 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@gmail.com>
Signed-off-by: Will Deacon <will@kernel.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;
-- 
2.25.0.rc1.283.g88dfdc4193-goog