linux-kernel - Re: [PATCH] seq_file: remove redundant assignment of index to m->index

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Date:   Sat, 10 Feb 2018 10:04:23 -0800
From:   Joe Perches <joe@...ches.com>
To:     Donglin Peng <dolinux.peng@...il.com>, viro@...iv.linux.org.uk
Cc:     linux-fsdevel@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] seq_file: remove redundant assignment of index to
 m->index

On Sat, 2018-02-10 at 23:59 +0800, Donglin Peng wrote:
> There are two redundant assignments in the traverse() function, because
> the while loop will break after these two assignments, and after that
> the variable index will be assigned to m->index again.
[]
> diff --git a/fs/seq_file.c b/fs/seq_file.c
[]
> @@ -120,14 +120,12 @@ static int traverse(struct seq_file *m, loff_t offset)
>          if (pos + m->count > offset) {
>              m->from = offset - pos;
>              m->count -= m->from;
> -            m->index = index;
>              break;
>          }
>          pos += m->count;
>          m->count = 0;
>          if (pos == offset) {
>              index++;
> -            m->index = index;
>              break;
>          }
>          p = m->op->next(m, p, &index);

Of course this looks correct, but how
are you _absolutely sure_ about this?

Perhaps the m->op->stop(m, p) call below
the break, which takes m as an argument,
needs an updated m->index.

Unless you can verify _all_ the indirect
paths that stop() can take, this patch may
not be correct.