linux-kernel - [PATCH] [RFC] io_uring: warning about unused-but-set parameter

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Date:   Mon, 20 Sep 2021 14:13:44 +0200
From:   Arnd Bergmann <arnd@...nel.org>
To:     Jens Axboe <axboe@...nel.dk>,
        Pavel Begunkov <asml.silence@...il.com>
Cc:     Arnd Bergmann <arnd@...db.de>, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] [RFC] io_uring: warning about unused-but-set parameter

From: Arnd Bergmann <arnd@...db.de>

When enabling -Wunused warnings by building with W=1, I get an
instance of the -Wunused-but-set-parameter warning in the io_uring code:

fs/io_uring.c: In function 'io_queue_async_work':
fs/io_uring.c:1445:61: error: parameter 'locked' set but not used [-Werror=unused-but-set-parameter]
 1445 | static void io_queue_async_work(struct io_kiocb *req, bool *locked)
      |                                                       ~~~~~~^~~~~~

There are very few warnings of this type, so it would be nice to enable
this by default and fix all the existing instances. I was almost
done, but this was added recently as a precaution to prevent code
from using the parameter, which could be done by either removing
the initialization, or by adding a (fake) use of the variable, which
I do here with the cast to void.

Fixes: f237c30a5610 ("io_uring: batch task work locking")
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 fs/io_uring.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 63b0425d6a32..36fbc7f06f5e 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1450,6 +1450,7 @@ static void io_queue_async_work(struct io_kiocb *req, bool *locked)
 
 	/* must not take the lock, NULL it as a precaution */
 	locked = NULL;
+	(void)locked;
 
 	BUG_ON(!tctx);
 	BUG_ON(!tctx->io_wq);
-- 
2.29.2