linux-kernel - Re: [PATCH] locking/ww-mutex: Fix uninitialized use of ret in test

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Date:   Wed, 22 Sep 2021 11:52:58 -0400
From:   Waiman Long <llong@...hat.com>
To:     Nathan Chancellor <nathan@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>
Cc:     Boqun Feng <boqun.feng@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        "kernelci.org bot" <bot@...nelci.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH] locking/ww-mutex: Fix uninitialized use of ret in
 test_aa()

On 9/22/21 10:58 AM, Nathan Chancellor wrote:
> Clang warns:
>
> kernel/locking/test-ww_mutex.c:138:7: error: variable 'ret' is used uninitialized whenever 'if' condition is true [-Werror,-Wsometimes-uninitialized]
>                  if (!ww_mutex_trylock(&mutex, &ctx)) {
>                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> kernel/locking/test-ww_mutex.c:172:9: note: uninitialized use occurs here
>          return ret;
>                 ^~~
> kernel/locking/test-ww_mutex.c:138:3: note: remove the 'if' if its condition is always false
>                  if (!ww_mutex_trylock(&mutex, &ctx)) {
>                  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> kernel/locking/test-ww_mutex.c:125:9: note: initialize the variable 'ret' to silence this warning
>          int ret;
>                 ^
>                  = 0
> 1 error generated.
>
> Assign !ww_mutex_trylock(...) to ret so that it is always initialized.
>
> Fixes: 12235da8c80a ("kernel/locking: Add context to ww_mutex_trylock()")
> Link: https://github.com/ClangBuiltLinux/linux/issues/1463
> Reported-by: "kernelci.org bot" <bot@...nelci.org>
> Reported-by: Stephen Rothwell <sfr@...b.auug.org.au>
> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---
>   kernel/locking/test-ww_mutex.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/locking/test-ww_mutex.c b/kernel/locking/test-ww_mutex.c
> index d63ac411f367..353004155d65 100644
> --- a/kernel/locking/test-ww_mutex.c
> +++ b/kernel/locking/test-ww_mutex.c
> @@ -135,7 +135,8 @@ static int test_aa(bool trylock)
>   			goto out;
>   		}
>   	} else {
> -		if (!ww_mutex_trylock(&mutex, &ctx)) {
> +		ret = !ww_mutex_trylock(&mutex, &ctx);
> +		if (ret) {
>   			pr_err("%s: initial trylock failed!\n", __func__);
>   			goto out;
>   		}
>
> base-commit: 12235da8c80a1f9909008e4ca6036d5772b81192

I was a bit confused by this patch at the beginning and then realized 
that it was supposed to be applied on top of the tip true, not the 
current mainline kernel.

Anyway, it looks good to me

Acked-by: Waiman Long <longman@...hat.com>