linux-kernel - Re: [PATCH] staging: android: ashmem: remove usage of list iterator after the loop body

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Date:   Sun, 20 Nov 2022 18:05:20 +0800
From:   IFsuse <ifsuse14@...il.com>
To:     Jakob Koschel <jakobkoschel@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Christian Brauner <brauner@...nel.org>,
        Hridya Valsaraju <hridya@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        linux-kernel@...r.kernel.org, linux-staging@...ts.linux.dev,
        Mike Rapoport <rppt@...nel.org>,
        Brian Johannesmeyer <bjohannesmeyer@...il.com>,
        Cristiano Giuffrida <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>
Subject: Re: [PATCH] staging: android: ashmem: remove usage of list iterator
 after the loop body


在 2022/4/1 上午5:39, Jakob Koschel 写道:
> In preparation to limit the scope of a list iterator to the list
> traversal loop, use a dedicated pointer to point to the found element
> [1].
>
> Before, the code implicitly used the head when no element was found
> when using &pos->list. Since the new variable is only set if an
> element was found, the head needs to be used explicitly if the
> variable is NULL.
>
> Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/ [1]
> Signed-off-by: Jakob Koschel <jakobkoschel@...il.com>
> ---
>   drivers/staging/android/ashmem.c | 21 ++++++++++++---------
>   1 file changed, 12 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
> index ddbde3f8430e..a1e245827cf6 100644
> --- a/drivers/staging/android/ashmem.c
> +++ b/drivers/staging/android/ashmem.c
> @@ -703,30 +703,33 @@ static int ashmem_pin(struct ashmem_area *asma, size_t pgstart, size_t pgend,
>   static int ashmem_unpin(struct ashmem_area *asma, size_t pgstart, size_t pgend,
>   			struct ashmem_range **new_range)
>   {
> -	struct ashmem_range *range, *next;
> +	struct ashmem_range *range = NULL, *iter, *next;
>   	unsigned int purged = ASHMEM_NOT_PURGED;
>   
>   restart:
> -	list_for_each_entry_safe(range, next, &asma->unpinned_list, unpinned) {
> +	list_for_each_entry_safe(iter, next, &asma->unpinned_list, unpinned) {
>   		/* short circuit: this is our insertion point */
> -		if (range_before_page(range, pgstart))
> +		if (range_before_page(iter, pgstart)) {
> +			range = iter;
>   			break;
> +		}
>   
>   		/*
>   		 * The user can ask us to unpin pages that are already entirely
>   		 * or partially pinned. We handle those two cases here.
>   		 */
> -		if (page_range_subsumed_by_range(range, pgstart, pgend))
> +		if (page_range_subsumed_by_range(iter, pgstart, pgend))
>   			return 0;
> -		if (page_range_in_range(range, pgstart, pgend)) {
> -			pgstart = min(range->pgstart, pgstart);
> -			pgend = max(range->pgend, pgend);
> -			purged |= range->purged;
> -			range_del(range);
> +		if (page_range_in_range(iter, pgstart, pgend)) {
> +			pgstart = min(iter->pgstart, pgstart);
> +			pgend = max(iter->pgend, pgend);
> +			purged |= iter->purged;
> +			range_del(iter);
>   			goto restart;
>   		}
>   	}
>   
> +	range = list_prepare_entry(range, &asma->unpinned_list, unpinned);
>   	range_alloc(asma, range, purged, pgstart, pgend, new_range);
>   	return 0;
>   }
>
> base-commit: f82da161ea75dc4db21b2499e4b1facd36dab275