linux-kernel - Re: [PATCH] ocfs2: remove useless code in ocfs2_try_to_merge

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Date: Tue, 16 Jan 2024 12:09:26 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Su Hui <suhui@...china.com>
Cc: mark@...heh.com, jlbec@...lplan.org, joseph.qi@...ux.alibaba.com,
 nathan@...nel.org, ndesaulniers@...gle.com, morbo@...gle.com,
 justinstitt@...gle.com, ocfs2-devel@...ts.linux.dev,
 linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
 kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] ocfs2: remove useless code in ocfs2_try_to_merge_extent

On Fri, 12 Jan 2024 12:26:40 +0800 Su Hui <suhui@...china.com> wrote:

> Clang static checker warning: Value stored to 'rec' is never read.
> Remove this useless code to silent this warning.
> 
> --- a/fs/ocfs2/alloc.c
> +++ b/fs/ocfs2/alloc.c
> @@ -3743,8 +3743,6 @@ static int ocfs2_try_to_merge_extent(handle_t *handle,
>  			goto out;
>  		}
>  
> -		rec = &el->l_recs[split_index];
> -
>  		/*
>  		 * Note that we don't pass split_rec here on purpose -
>  		 * we've merged it into the rec already.

Then:

		ret = ocfs2_merge_rec_left(path, handle, et, rec,
					   dealloc, split_index);

and ocfs2_merge_rec_left() almost immediately dereferences `rec'.

So this looks quite wrong to me.