Re: [PATCH] nvdimm-btt: simplify code with the scope based resource management

[dinghao.liu@zju.edu.cn]

> 
> On 12/10/23 03:27, Dinghao Liu wrote:
> > Use the scope based resource management (defined in
> > linux/cleanup.h) to automate resource lifetime
> > control on struct btt_sb *super in discover_arenas().
> > 
> > Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
> > ---
> >  drivers/nvdimm/btt.c | 12 ++++--------
> >  1 file changed, 4 insertions(+), 8 deletions(-)
> > 
> > diff --git a/drivers/nvdimm/btt.c b/drivers/nvdimm/btt.c
> > index d5593b0dc700..ff42778b51de 100644
> > --- a/drivers/nvdimm/btt.c
> > +++ b/drivers/nvdimm/btt.c
> > @@ -16,6 +16,7 @@
> >  #include <linux/fs.h>
> >  #include <linux/nd.h>
> >  #include <linux/backing-dev.h>
> > +#include <linux/cleanup.h>
> >  #include "btt.h"
> >  #include "nd.h"
> >  
> > @@ -847,7 +848,7 @@ static int discover_arenas(struct btt *btt)
> >  {
> >  	int ret = 0;
> >  	struct arena_info *arena;
> > -	struct btt_sb *super;
> > +	struct btt_sb *super __free(kfree) = NULL;
> >  	size_t remaining = btt->rawsize;
> >  	u64 cur_nlba = 0;
> >  	size_t cur_off = 0;
> > @@ -860,10 +861,8 @@ static int discover_arenas(struct btt *btt)
> >  	while (remaining) {
> >  		/* Alloc memory for arena */
> >  		arena = alloc_arena(btt, 0, 0, 0);
> > -		if (!arena) {
> > -			ret = -ENOMEM;
> > -			goto out_super;
> > -		}
> > +		if (!arena)
> > +			return -ENOMEM;
> >  
> >  		arena->infooff = cur_off;
> >  		ret = btt_info_read(arena, super);
> > @@ -919,14 +918,11 @@ static int discover_arenas(struct btt *btt)
> >  	btt->nlba = cur_nlba;
> >  	btt->init_state = INIT_READY;
> >  
> > -	kfree(super);
> >  	return ret;
> >  
> >   out:
> >  	kfree(arena);
> >  	free_arenas(btt);
> > - out_super:
> > -	kfree(super);
> >  	return ret;
> >  }
> >  
> 
> I would do the allocation like something below for the first chunk. Otherwise the rest LGTM. 
> 
> diff --git a/drivers/nvdimm/btt.c b/drivers/nvdimm/btt.c
> index d5593b0dc700..143921e7f26c 100644
> --- a/drivers/nvdimm/btt.c
> +++ b/drivers/nvdimm/btt.c
> @@ -16,6 +16,7 @@
>  #include <linux/fs.h>
>  #include <linux/nd.h>
>  #include <linux/backing-dev.h>
> +#include <linux/cleanup.h>
>  #include "btt.h"
>  #include "nd.h"
>  
> @@ -845,25 +846,23 @@ static void parse_arena_meta(struct arena_info *arena, struct btt_sb *super,
>  
>  static int discover_arenas(struct btt *btt)
>  {
> +       struct btt_sb *super __free(kfree) =
> +               kzalloc(sizeof(*super), GFP_KERNEL);
>         int ret = 0;
>         struct arena_info *arena;
> -       struct btt_sb *super;
>         size_t remaining = btt->rawsize;
>         u64 cur_nlba = 0;
>         size_t cur_off = 0;
>         int num_arenas = 0;
>  
> -       super = kzalloc(sizeof(*super), GFP_KERNEL);
>         if (!super)
>                 return -ENOMEM;
>  
>         while (remaining) {
>                 /* Alloc memory for arena */

It's a little strange that we do not check super immediately after allocation.
How about this:

 static int discover_arenas(struct btt *btt)
 {
        int ret = 0;
        struct arena_info *arena;
-       struct btt_sb *super;
        size_t remaining = btt->rawsize;
        u64 cur_nlba = 0;
        size_t cur_off = 0;
        int num_arenas = 0;
 
-       super = kzalloc(sizeof(*super), GFP_KERNEL);
+       struct btt_sb *super __free(kfree) = 
+               kzalloc(sizeof(*super), GFP_KERNEL);
        if (!super)
                return -ENOMEM;
 
        while (remaining) {