linux-kernel - Re: [PATCH] scsi: lpfc: avoid usage of list iterator variable after loop

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Message-ID: <CABPRKS_NjBM_fW++PD5Az=9vEuhn=0-mtBg+a37P4i8HyVXcOg@mail.gmail.com>
Date:   Wed, 1 Mar 2023 15:01:18 -0800
From:   Justin Tee <justintee8345@...il.com>
To:     Jakob Koschel <jkl820.git@...il.com>, linux-scsi@...r.kernel.org
Cc:     James Smart <james.smart@...adcom.com>,
        Dick Kennedy <dick.kennedy@...adcom.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        linux-kernel@...r.kernel.org,
        Pietro Borrello <borrello@...g.uniroma1.it>,
        Cristiano Giuffrida <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>, Justin Tee <justin.tee@...adcom.com>
Subject: Re: [PATCH] scsi: lpfc: avoid usage of list iterator variable after loop

On Wed, Mar 1, 2023 at 9:30 AM Jakob Koschel <jkl820.git@...il.com> wrote:
>
> If the &epd_pool->list is empty when executing
> lpfc_get_io_buf_from_expedite_pool() the function would return an
> invalid pointer. Even in the case if the list is guaranteed to be
> populated, the iterator variable should not be used after the loop to be
> more robust for future changes.
>
> Linus proposed to avoid any use of the list iterator variable after the
> loop, in the attempt to move the list iterator variable declaration into
> the marcro to avoid any potential misuse after the loop [1].
>
> Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/ [1]
> Signed-off-by: Jakob Koschel <jkl820.git@...il.com>
> ---
>  drivers/scsi/lpfc/lpfc_sli.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/scsi/lpfc/lpfc_sli.c b/drivers/scsi/lpfc/lpfc_sli.c
> index edbd81c3b643..5d06bf6d4f39 100644
> --- a/drivers/scsi/lpfc/lpfc_sli.c
> +++ b/drivers/scsi/lpfc/lpfc_sli.c
> @@ -21899,20 +21899,20 @@ lpfc_get_io_buf_from_private_pool(struct lpfc_hba *phba,
>  static struct lpfc_io_buf *
>  lpfc_get_io_buf_from_expedite_pool(struct lpfc_hba *phba)
>  {
> -       struct lpfc_io_buf *lpfc_ncmd;
> +       struct lpfc_io_buf *lpfc_ncmd = NULL, *iter;
>         struct lpfc_io_buf *lpfc_ncmd_next;
>         unsigned long iflag;
>         struct lpfc_epd_pool *epd_pool;
>
>         epd_pool = &phba->epd_pool;
> -       lpfc_ncmd = NULL;
>
>         spin_lock_irqsave(&epd_pool->lock, iflag);
>         if (epd_pool->count > 0) {
> -               list_for_each_entry_safe(lpfc_ncmd, lpfc_ncmd_next,
> +               list_for_each_entry_safe(iter, lpfc_ncmd_next,
>                                          &epd_pool->list, list) {
> -                       list_del(&lpfc_ncmd->list);
> +                       list_del(&iter->list);
>                         epd_pool->count--;
> +                       lpfc_ncmd = iter;
>                         break;
>                 }
>         }
>
> ---
> base-commit: c0927a7a5391f7d8e593e5e50ead7505a23cadf9
> change-id: 20230301-scsi-lpfc-avoid-list-iterator-after-loop-7b7d5c3a8efc
>
> Best regards,
> --
> Jakob Koschel <jkl820.git@...il.com>
>

Reviewed-by: Justin Tee <justin.tee@...adcom.com>

Thanks looks fine.

Regards,
Justin