linux-kernel - Re: [uml-devel] [PATCH 4/4] UML

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Date:	Wed, 21 Feb 2007 23:40:28 +0100
From:	Blaisorblade <blaisorblade@...oo.it>
To:	user-mode-linux-devel@...ts.sourceforge.net
Cc:	Jeff Dike <jdike@...toit.com>, akpm@...l.org,
	linux-kernel@...r.kernel.org
Subject: Re: [uml-devel] [PATCH 4/4] UML - lock host ldt retrieval

On Wednesday 21 February 2007 21:25, Jeff Dike wrote:
> Add some locking to host_ldt_entries to prevent racing when reading
> LDT information from the host.

Please remove GFP_KERNEL allocation under spin_lock - simplest way is using a 
mutex unless this can be important for performance.

> @@ -386,15 +387,20 @@ static long do_modify_ldt_skas(int func,
>  	return ret;
>  }
>
> -short dummy_list[9] = {0, -1};
> -short * host_ldt_entries = NULL;
> +static DEFINE_SPINLOCK(host_ldt_lock);
> +static short dummy_list[9] = {0, -1};
> +static short * host_ldt_entries = NULL;
>
> -void ldt_get_host_info(void)
> +static void ldt_get_host_info(void)
>  {
>  	long ret;
>  	struct ldt_entry * ldt;
>  	int i, size, k, order;
>
> +	spin_lock(&host_ldt_lock);
> +	if(host_ldt_entries != NULL)
> +		goto out_unlock;
> +
>  	host_ldt_entries = dummy_list+1;
>
>  	for(i = LDT_PAGES_MAX-1, order=0; i; i>>=1, order++);
> @@ -402,8 +408,9 @@ void ldt_get_host_info(void)
>  	ldt = (struct ldt_entry *)
>  	      __get_free_pages(GFP_KERNEL|__GFP_ZERO, order);
>  	if(ldt == NULL) {
> -		printk("ldt_get_host_info: couldn't allocate buffer for host ldt\n");
> -		return;
> +		printk("ldt_get_host_info: couldn't allocate buffer for host "
> +		       "ldt\n");
> +		goto out_unlock;
>  	}
>
>  	ret = modify_ldt(0, ldt, (1<<order)*PAGE_SIZE);
> @@ -428,7 +435,8 @@ void ldt_get_host_info(void)
>  		size = (size + 1) * sizeof(dummy_list[0]);
>  		host_ldt_entries = kmalloc(size, GFP_KERNEL);
>  		if(host_ldt_entries == NULL) {
> -			printk("ldt_get_host_info: couldn't allocate host ldt list\n");
> +			printk("ldt_get_host_info: couldn't allocate host ldt "
> +			       "list\n");
>  			goto out_free;
>  		}
>  	}
> @@ -442,6 +450,8 @@ void ldt_get_host_info(void)
>
>  out_free:
>  	free_pages((unsigned long)ldt, order);
> +out_unlock:
> +	spin_unlock(&host_ldt_lock);
>  }
>
>  long init_new_ldt(struct mmu_context_skas * new_mm,
> @@ -480,8 +490,7 @@ long init_new_ldt(struct mmu_context_ska
>  			 * inherited from the host. All ldt-entries found
>  			 * will be reset in the following loop
>  			 */
> -			if(host_ldt_entries == NULL)
> -				ldt_get_host_info();
> +			ldt_get_host_info();
>  			for(num_p=host_ldt_entries; *num_p != -1; num_p++){
>  				desc.entry_number = *num_p;
>  				err = write_ldt_entry(&new_mm->id, 1, &desc,
> @@ -560,6 +569,6 @@ void free_ldt(struct mmu_context_skas *
>
>  int sys_modify_ldt(int func, void __user *ptr, unsigned long bytecount)
>  {
> -	return(CHOOSE_MODE_PROC(do_modify_ldt_tt, do_modify_ldt_skas, func,
> -	                        ptr, bytecount));
> +	return CHOOSE_MODE_PROC(do_modify_ldt_tt, do_modify_ldt_skas, func,
> +	                        ptr, bytecount);
>  }
>
>
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-- 
Inform me of my mistakes, so I can add them to my list!
Paolo Giarrusso, aka Blaisorblade
http://www.user-mode-linux.org/~blaisorblade
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