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From:   Muchun Song <songmuchun@bytedance.com>
Date:   Tue, 14 Jun 2022 17:26:00 +0800
Message-ID: <CAMZfGtWswvFRp8UmnETRENsq1WBx9QvG7A_v8Eq62aaNA96wMw@mail.gmail.com>
Subject: Re: [PATCH] fs: io_uring: remove NULL check before kfree
To:     Dongliang Mu <dzm91@hust.edu.cn>
Cc:     Jens Axboe <axboe@kernel.dk>,
        Pavel Begunkov <asml.silence@gmail.com>,
        mudongliang <mudongliangabcd@gmail.com>,
        io-uring@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>
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On Tue, Jun 14, 2022 at 5:14 PM Dongliang Mu <dzm91@hust.edu.cn> wrote:
>
> From: mudongliang <mudongliangabcd@gmail.com>
>
> kfree can handle NULL pointer as its argument.
> According to coccinelle isnullfree check, remove NULL check
> before kfree operation.
>
> Signed-off-by: mudongliang <mudongliangabcd@gmail.com>
> ---
>  fs/io_uring.c | 15 +++++----------
>  1 file changed, 5 insertions(+), 10 deletions(-)
>
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 3aab4182fd89..bec47eae2a9b 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -3159,8 +3159,7 @@ static void io_free_batch_list(struct io_ring_ctx *ctx,
>                         if ((req->flags & REQ_F_POLLED) && req->apoll) {
>                                 struct async_poll *apoll = req->apoll;
>
> -                               if (apoll->double_poll)
> -                                       kfree(apoll->double_poll);
> +                               kfree(apoll->double_poll);
>                                 list_add(&apoll->poll.wait.entry,
>                                                 &ctx->apoll_cache);
>                                 req->flags &= ~REQ_F_POLLED;
> @@ -4499,8 +4498,7 @@ static int io_read(struct io_kiocb *req, unsigned int issue_flags)
>         kiocb_done(req, ret, issue_flags);
>  out_free:
>         /* it's faster to check here then delegate to kfree */

I am feeling you are not on the right way. See the comment
here.

Thanks.

> -       if (iovec)
> -               kfree(iovec);
> +       kfree(iovec);
>         return 0;
>  }
>
> @@ -4602,8 +4600,7 @@ static int io_write(struct io_kiocb *req, unsigned int issue_flags)
>         }
>  out_free:
>         /* it's reportedly faster than delegating the null check to kfree() */

See here.

> -       if (iovec)
> -               kfree(iovec);
> +       kfree(iovec);
>         return ret;
>  }
>
> @@ -6227,8 +6224,7 @@ static int io_sendmsg(struct io_kiocb *req, unsigned int issue_flags)
>                 req_set_fail(req);
>         }
>         /* fast path, check for non-NULL to avoid function call */

here.

> -       if (kmsg->free_iov)
> -               kfree(kmsg->free_iov);
> +       kfree(kmsg->free_iov);
>         req->flags &= ~REQ_F_NEED_CLEANUP;
>         if (ret >= 0)
>                 ret += sr->done_io;
> @@ -6481,8 +6477,7 @@ static int io_recvmsg(struct io_kiocb *req, unsigned int issue_flags)
>         }
>
>         /* fast path, check for non-NULL to avoid function call */

And here.

> -       if (kmsg->free_iov)
> -               kfree(kmsg->free_iov);
> +       kfree(kmsg->free_iov);
>         req->flags &= ~REQ_F_NEED_CLEANUP;
>         if (ret >= 0)
>                 ret += sr->done_io;
> --
> 2.35.1
>