linux-kernel - Re: [Outreachy kernel] [PATCH 1/5] staging: lustre: Use list_for_each_entry

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Message-ID: <alpine.DEB.2.20.1703051829270.3052@hadrien>
Date:   Sun, 5 Mar 2017 18:34:05 +0100 (CET)
From:   Julia Lawall <julia.lawall@...6.fr>
To:     simran singhal <singhalsimran0@...il.com>
cc:     oleg.drokin@...el.com, andreas.dilger@...el.com,
        jsimmons@...radead.org, gregkh@...uxfoundation.org,
        lustre-devel@...ts.lustre.org, devel@...verdev.osuosl.org,
        linux-kernel@...r.kernel.org, outreachy-kernel@...glegroups.com
Subject: Re: [Outreachy kernel] [PATCH 1/5] staging: lustre: Use
 list_for_each_entry_safe



On Sun, 5 Mar 2017, simran singhal wrote:

> Doubly linked lists which are  iterated  using list_empty
> and list_entry macros have been replaced with list_for_each_entry_safe
> macro.
> This makes the iteration simpler and more readable.
>
> This patch replaces the while loop containing list_empty and list_entry
> with list_for_each_entry_safe.
>
> This was done with Coccinelle.
>
> @@
> expression E1;
> identifier I1, I2;
> type T;
> iterator name list_for_each_entry_safe;
> @@
>
> T *I1;
> + T *tmp;
> ...

The function that is modified in this patch actually has another
opportunity.  That doesn't get transformed because with ... Coccinelle
matches the shortest path between what comes before and what comes after,
and so it only matches the first while loop.

You could sort of fix the problem by putting when any on the ...  That
allows anything in the path, including other while loops.

That though will mean that you will try to add two instances of the tmp
declaration after the declaration of I1.  Coccinelle allows adding only
one thing, unless the + is replaced by ++.  But if you do that, you will
get two decarations of tmp.

So either make the second change by hand, or let Coccinelle do it an
remove the second declaration of tmp by hand.

julia

> - while (list_empty(&E1) == 0)
> + list_for_each_entry_safe (I1, tmp, &E1, I2)
> {
> ...when != T *I1;
> - I1 = list_entry(E1.next, T, I2);
> ...
> }
>
> Signed-off-by: simran singhal <singhalsimran0@...il.com>
> ---
>  drivers/staging/lustre/lustre/ptlrpc/service.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/staging/lustre/lustre/ptlrpc/service.c b/drivers/staging/lustre/lustre/ptlrpc/service.c
> index b8091c1..4e7dc1d 100644
> --- a/drivers/staging/lustre/lustre/ptlrpc/service.c
> +++ b/drivers/staging/lustre/lustre/ptlrpc/service.c
> @@ -2314,6 +2314,7 @@ static void ptlrpc_svcpt_stop_threads(struct ptlrpc_service_part *svcpt)
>  {
>  	struct l_wait_info lwi = { 0 };
>  	struct ptlrpc_thread *thread;
> +	struct ptlrpc_thread *tmp;
>  	LIST_HEAD(zombie);
>
>  	CDEBUG(D_INFO, "Stopping threads for service %s\n",
> @@ -2329,9 +2330,7 @@ static void ptlrpc_svcpt_stop_threads(struct ptlrpc_service_part *svcpt)
>
>  	wake_up_all(&svcpt->scp_waitq);
>
> -	while (!list_empty(&svcpt->scp_threads)) {
> -		thread = list_entry(svcpt->scp_threads.next,
> -				    struct ptlrpc_thread, t_link);
> +	list_for_each_entry_safe(thread, tmp, &svcpt->scp_threads, t_link) {
>  		if (thread_is_stopped(thread)) {
>  			list_del(&thread->t_link);
>  			list_add(&thread->t_link, &zombie);
> --
> 2.7.4
>
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