Re: [uml-devel] [PATCH v3] um: net: replace GFP_KERNEL with GFP_ATOMIC when spinlock is held

[Joe Perches]

On Thu, 2015-10-29 at 14:46 +0530, Saurabh Sengar wrote:
> replace GFP_KERNEL with GFP_ATOMIC while spinlock is held,
> as code while holding a spinlock should be atomic.
> GFP_KERNEL may sleep and can cause deadlock,
> where as GFP_ATOMIC may fail but certainly avoids deadlock
> 
> Signed-off-by: Saurabh Sengar <saurabh.tr...@gmail.com>
> ---
> v3: removed the atomic variable, as per Richard comment

Trivia: You could remove the gfp_mask variables too
        and just use GFP_KERNEL and GFP_ATOMIC directly.

> diff --git a/arch/um/drivers/net_kern.c b/arch/um/drivers/net_kern.c
[]
> @@ -600,20 +600,22 @@ void register_transport(struct transport *new)
>       void *init;
>       char *mac = NULL;
>       int match;
> +     int gfp_mask;
>  
>       spin_lock(&transports_lock);
>       BUG_ON(!list_empty(&new->list));
>       list_add(&new->list, &transports);
>       spin_unlock(&transports_lock);
>  
> +     gfp_mask = GFP_KERNEL;
>       list_for_each_safe(ele, next, &eth_cmd_line) {
>               eth = list_entry(ele, struct eth_init, list);
>               match = check_transport(new, eth->init, eth->index, &init,
> -                                     &mac);
> +                                     &mac, gfp_mask);
>               if (!match)
>                       continue;
>               else if (init != NULL) {
> -                     eth_configure(eth->index, init, mac, new);
> +                     eth_configure(eth->index, init, mac, new, gfp_mask);
>                       kfree(init);
>               }
>               list_del(&eth->list);
> @@ -627,14 +629,17 @@ static int eth_setup_common(char *str, int index)
>       void *init;
>       char *mac = NULL;
>       int found = 0;
> +     int gfp_mask;
>  
>       spin_lock(&transports_lock);
> +     gfp_mask = GFP_ATOMIC;
>       list_for_each(ele, &transports) {
>               transport = list_entry(ele, struct transport, list);
> -             if (!check_transport(transport, str, index, &init, &mac))
> +             if (!check_transport(transport, str, index, &init,
> +                                                     &mac, gfp_mask))
>                       continue;
>               if (init != NULL) {
> -                     eth_configure(index, init, mac, transport);
> +                     eth_configure(index, init, mac, transport, gfp_mask);
>                       kfree(init);
>               }
>               found = 1;




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