linux-kernel - Re: [PATCH] kernel/resource: Fix use of ternary condition in release_mem_region

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Message-ID: <20201009092433.GA56924@L-31X9LVDL-1304.local>
Date:   Fri, 9 Oct 2020 17:24:33 +0800
From:   Wei Yang <richard.weiyang@...ux.alibaba.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     david@...hat.com, akpm@...ux-foundation.org, ardb@...nel.org,
        bhe@...hat.com, dan.j.williams@...el.com, jgg@...pe.ca,
        keescook@...omium.org, linux-acpi@...r.kernel.org,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-nvdimm@...ts.01.org,
        linux-s390@...r.kernel.org, mhocko@...e.com,
        pankaj.gupta.linux@...il.com, richardw.yang@...ux.intel.com,
        virtualization@...ts.linux-foundation.org,
        xen-devel@...ts.xenproject.org, clang-built-linux@...glegroups.com
Subject: Re: [PATCH] kernel/resource: Fix use of ternary condition in
 release_mem_region_adjustable

On Mon, Sep 21, 2020 at 11:07:48PM -0700, Nathan Chancellor wrote:
>Clang warns:
>
>kernel/resource.c:1281:53: warning: operator '?:' has lower precedence
>than '|'; '|' will be evaluated first
>[-Wbitwise-conditional-parentheses]
>        new_res = alloc_resource(GFP_KERNEL | alloc_nofail ? __GFP_NOFAIL : 0);
>                                 ~~~~~~~~~~~~~~~~~~~~~~~~~ ^
>kernel/resource.c:1281:53: note: place parentheses around the '|'
>expression to silence this warning
>        new_res = alloc_resource(GFP_KERNEL | alloc_nofail ? __GFP_NOFAIL : 0);
>                                 ~~~~~~~~~~~~~~~~~~~~~~~~~ ^
>kernel/resource.c:1281:53: note: place parentheses around the '?:'
>expression to evaluate it first
>        new_res = alloc_resource(GFP_KERNEL | alloc_nofail ? __GFP_NOFAIL : 0);
>                                                           ^
>                                              (                              )
>1 warning generated.
>
>Add the parentheses as it was clearly intended for the ternary condition
>to be evaluated first.
>
>Fixes: 5fd23bd0d739 ("kernel/resource: make release_mem_region_adjustable() never fail")
>Link: https://github.com/ClangBuiltLinux/linux/issues/1159
>Signed-off-by: Nathan Chancellor <natechancellor@...il.com>

Reviewed-by: Wei Yang <richard.weiyang@...ux.alibaba.com>

>---
>
>Presumably, this will be squashed but I included a fixes tag
>nonetheless. Apologies if this has already been noticed and fixed
>already, I did not find anything on LKML.
>
> kernel/resource.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
>diff --git a/kernel/resource.c b/kernel/resource.c
>index ca2a666e4317..3ae2f56cc79d 100644
>--- a/kernel/resource.c
>+++ b/kernel/resource.c
>@@ -1278,7 +1278,7 @@ void release_mem_region_adjustable(resource_size_t start, resource_size_t size)
> 	 * similarly).
> 	 */
> retry:
>-	new_res = alloc_resource(GFP_KERNEL | alloc_nofail ? __GFP_NOFAIL : 0);
>+	new_res = alloc_resource(GFP_KERNEL | (alloc_nofail ? __GFP_NOFAIL : 0));
> 
> 	p = &parent->child;
> 	write_lock(&resource_lock);
>
>base-commit: 40ee82f47bf297e31d0c47547cd8f24ede52415a
>-- 
>2.28.0

-- 
Wei Yang
Help you, Help me