linux-kernel - Re: [PATCH 5/5] staging: lustre: osc_page.c: Use list_for_each_entry

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Date:   Mon, 6 Mar 2017 15:20:49 +0000 (GMT)
From:   James Simmons <jsimmons@...radead.org>
To:     simran singhal <singhalsimran0@...il.com>
cc:     oleg.drokin@...el.com, andreas.dilger@...el.com,
        gregkh@...uxfoundation.org, lustre-devel@...ts.lustre.org,
        devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org,
        outreachy-kernel@...glegroups.com
Subject: Re: [PATCH 5/5] staging: lustre: osc_page.c:  Use
 list_for_each_entry_safe


> 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;
> ...
> - 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>

NAK!!!!!!

This change was reverted in commit 

cd15dd6ef4ea11df87f717b8b1b83aaa738ec8af

Doing these while (list_empty(..)) to list_for_entry...
are not simple changes and have broken things in lustre
before. Unless you really understand the state machine of
the lustre code I don't recommend these kinds of change
for lustre.

> ---
>  drivers/staging/lustre/lustre/osc/osc_page.c | 11 ++++-------
>  1 file changed, 4 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/staging/lustre/lustre/osc/osc_page.c b/drivers/staging/lustre/lustre/osc/osc_page.c
> index ed8a0dc..e8b974f 100644
> --- a/drivers/staging/lustre/lustre/osc/osc_page.c
> +++ b/drivers/staging/lustre/lustre/osc/osc_page.c
> @@ -542,6 +542,7 @@ long osc_lru_shrink(const struct lu_env *env, struct client_obd *cli,
>  	struct cl_object *clobj = NULL;
>  	struct cl_page **pvec;
>  	struct osc_page *opg;
> +	struct osc_page *tmp;
>  	int maxscan = 0;
>  	long count = 0;
>  	int index = 0;
> @@ -572,7 +573,7 @@ long osc_lru_shrink(const struct lu_env *env, struct client_obd *cli,
>  	if (force)
>  		cli->cl_lru_reclaim++;
>  	maxscan = min(target << 1, atomic_long_read(&cli->cl_lru_in_list));
> -	while (!list_empty(&cli->cl_lru_list)) {
> +	list_for_each_entry_safe(opg, tmp, &cli->cl_lru_list, ops_lru) {
>  		struct cl_page *page;
>  		bool will_free = false;
>  
> @@ -582,8 +583,6 @@ long osc_lru_shrink(const struct lu_env *env, struct client_obd *cli,
>  		if (--maxscan < 0)
>  			break;
>  
> -		opg = list_entry(cli->cl_lru_list.next, struct osc_page,
> -				 ops_lru);
>  		page = opg->ops_cl.cpl_page;
>  		if (lru_page_busy(cli, page)) {
>  			list_move_tail(&opg->ops_lru, &cli->cl_lru_list);
> @@ -1043,6 +1042,7 @@ unsigned long osc_cache_shrink_scan(struct shrinker *sk,
>  {
>  	struct client_obd *stop_anchor = NULL;
>  	struct client_obd *cli;
> +	struct client_obd *tmp;
>  	struct lu_env *env;
>  	long shrank = 0;
>  	u16 refcheck;
> @@ -1059,10 +1059,7 @@ unsigned long osc_cache_shrink_scan(struct shrinker *sk,
>  		return SHRINK_STOP;
>  
>  	spin_lock(&osc_shrink_lock);
> -	while (!list_empty(&osc_shrink_list)) {
> -		cli = list_entry(osc_shrink_list.next, struct client_obd,
> -				 cl_shrink_list);
> -
> +	list_for_each_entry_safe(cli, tmp, &osc_shrink_list, cl_shrink_list) {
>  		if (!stop_anchor)
>  			stop_anchor = cli;
>  		else if (cli == stop_anchor)
> -- 
> 2.7.4
> 
>