linux-kernel - Re: [PATCH] scsi: fnic: Use kmalloc instead of vmalloc for a small memory allocation

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Date:   Fri, 24 Apr 2020 12:30:30 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     satishkh@...co.com, sebaddel@...co.com, kartilak@...co.com,
        jejb@...ux.ibm.com, martin.petersen@...cle.com,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] scsi: fnic: Use kmalloc instead of vmalloc for a small
 memory allocation

On Thu, Apr 23, 2020 at 10:46:20PM +0200, Christophe JAILLET wrote:
> 'struct fc_trace_flag_type' is just a few bytes long. There is no need
> to allocate such a structure with vmalloc. Using kmalloc instead.
> 
> While at it, axe a useless test when freeing the memory.
> 
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
>  drivers/scsi/fnic/fnic_debugfs.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/scsi/fnic/fnic_debugfs.c b/drivers/scsi/fnic/fnic_debugfs.c
> index 13f7d88d6e57..8d6ce3470594 100644
> --- a/drivers/scsi/fnic/fnic_debugfs.c
> +++ b/drivers/scsi/fnic/fnic_debugfs.c
> @@ -58,8 +58,7 @@ int fnic_debugfs_init(void)
>  						fnic_trace_debugfs_root);
>  
>  	/* Allocate memory to structure */
> -	fc_trc_flag = (struct fc_trace_flag_type *)
> -		vmalloc(sizeof(struct fc_trace_flag_type));
> +	fc_trc_flag = kmalloc(sizeof(*fc_trc_flag), GFP_KERNEL);
>  
>  	if (fc_trc_flag) {

I hate success handling... This test should be reversed so that we do
error handling. It should return -ENOMEM instead of 0 on allocation
failure, otherwise it leads to a NULL dereference down the road.
Although, of course in current kernel small size allocations like this
never fail in real life.

The other thing I wonder is if we should just replace the vmalloc()
implementation with kvmalloc().  IOW rename vmalloc() to __vmalloc() and
"#define vmalloc kvmalloc" (not literally).  That was allocations of
less than a page would always be done with kmalloc().

regards,
dan carpenter