linux-kernel - Re: [PATCH 2/3] afs: check function return

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Date:   Mon, 12 Jul 2021 11:20:47 -0300
From:   Marc Dionne <marc.c.dionne@...il.com>
To:     David Howells <dhowells@...hat.com>
Cc:     linux-afs@...ts.infradead.org, Tom Rix <trix@...hat.com>,
        linux-fsdevel@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] afs: check function return

On Mon, Jul 12, 2021 at 9:57 AM David Howells <dhowells@...hat.com> wrote:
>
> From: Tom Rix <trix@...hat.com>
>
> Static analysis reports this problem
>
> write.c:773:29: warning: Assigned value is garbage or undefined
>   mapping->writeback_index = next;
>                            ^ ~~~~
> The call to afs_writepages_region() can return without setting
> next.  So check the function return before using next.
>
> Fixes: e87b03f5830e ("afs: Prepare for use of THPs")
> Signed-off-by: Tom Rix <trix@...hat.com>
> Signed-off-by: David Howells <dhowells@...hat.com>
> Link: https://lore.kernel.org/r/20210430155031.3287870-1-trix@redhat.com
> ---
>
>  fs/afs/write.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/afs/write.c b/fs/afs/write.c
> index 3104b62c2082..2794147f82ff 100644
> --- a/fs/afs/write.c
> +++ b/fs/afs/write.c
> @@ -777,7 +777,7 @@ int afs_writepages(struct address_space *mapping,
>                 mapping->writeback_index = next / PAGE_SIZE;

Isn't there the same issue with the use of next here.

>         } else if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) {
>                 ret = afs_writepages_region(mapping, wbc, 0, LLONG_MAX, &next);
> -               if (wbc->nr_to_write > 0)
> +               if (wbc->nr_to_write > 0 && ret == 0)
>                         mapping->writeback_index = next;

Unrelated to this patch, but since next is a byte offset, should this
also divide by PAGE_SIZE as above.

>         } else {
>                 ret = afs_writepages_region(mapping, wbc,
>
>

Marc