Re: [PATCH 0/3] mm: mempolicy: the failure processing about mpol_to_str()

[Chen Gang F T <chen.gang.flying.transformer@gmail.com>]

On 08/20/2013 04:09 PM, Chen Gang wrote:
> On 08/20/2013 03:51 PM, Chen Gang wrote:
>> On 08/20/2013 03:48 PM, Chen Gang wrote:
>>> On 08/20/2013 02:47 PM, Cyrill Gorcunov wrote:
>>>> On Tue, Aug 20, 2013 at 01:41:40PM +0800, Chen Gang wrote:
>>>>>
>>>>>> sure you'll have to change shmem_show_mpol statement to return int code.
>>>>>> Won't this be more short and convenient?
>>>>>>
>>>>>>
>>>>>
>>>>> Hmm... if return -ENOSPC, in common processing, it still need continue
>>>>> (but need let outside know about the string truncation).
>>>>>
>>>>> So I still suggest to give more check for it.
>>>>
>>>> I still don't like adding additional code like
>>>>
>>>> +	ret = mpol_to_str(buffer, sizeof(buffer), mpol);
>>>> +	if (ret < 0)
>>>> +               switch (ret) {
>>>> +               case -ENOSPC:
>>>> +                       printk(KERN_WARNING
>>>> +                               "in %s: string is truncated in mpol_to_str().\n",
>>>> +                               __func__);
>>
>> Oh, that need 'break' in my original patch. :-)
>>
>>>> +               default:
>>>> +                       printk(KERN_ERR
>>>> +                               "in %s: call mpol_to_str() fail, errcode: %d. buffer: %p, size: %zu, pol: %p\n",
>>>> +                               __func__, ret, buffer, sizeof(buffer), mpol);
>>>> +                       return;
>>>> +               }
>>>>
>>>> this code is pretty neat for debugging purpose I think but in most case (if
>>>> only I've not missed something obvious) it simply won't be the case.
>>>>
>>>
>>> For mpol_to_str(), it is for printing string, I suggest to fill buffer
>>> as full as possible like another printing string functions, -ENOSPC is
>>> not critical error, callers may can bear it, and still want to continue.
>>>
>>> For 2 callers, I still suggest to process '-ENOSPC' and continue, it is
>>> really not a critical error, they can continue.
>>>
>>> For the 'default' error processing:
>>>
>>>   I still suggest to 'printk' in shmem_show_mpol(), because when failure occurs, it has no return value to mark the failure to upper caller.
>>>   Hmm... but for show_numa_map(), may remove the 'printk', only return the error code is OK. :-)
>>>
>>>
>>> Thanks.
>>>
> 
> Oh, for '-ENOSPC', it means critical error, it is my fault.
> 
> So, for simplify thinking and implementation, use your patch below is OK
> to me (but I suggest to print error information in the none return value
> function).
> 
> :-)
> 
>>>> Won't somthing like below do the same but with smaller code change?
>>>> Note I've not even compiled it but it shows the idea.
>>>> ---
>>>>  fs/proc/task_mmu.c |    4 +++-
>>>>  mm/shmem.c         |   17 +++++++++--------
>>>>  2 files changed, 12 insertions(+), 9 deletions(-)
>>>>
>>>> Index: linux-2.6.git/fs/proc/task_mmu.c
>>>> ===================================================================
>>>> --- linux-2.6.git.orig/fs/proc/task_mmu.c
>>>> +++ linux-2.6.git/fs/proc/task_mmu.c
>>>> @@ -1402,8 +1402,10 @@ static int show_numa_map(struct seq_file
>>>>  	walk.mm = mm;
>>>>  
>>>>  	pol = get_vma_policy(task, vma, vma->vm_start);
>>>> -	mpol_to_str(buffer, sizeof(buffer), pol);
>>>> +	n = mpol_to_str(buffer, sizeof(buffer), pol);
>>>>  	mpol_cond_put(pol);
>>>> +	if (n < 0)
>>>> +		return n;
>>>>  
>>>>  	seq_printf(m, "%08lx %s", vma->vm_start, buffer);
>>>>  
>>>> Index: linux-2.6.git/mm/shmem.c
>>>> ===================================================================
>>>> --- linux-2.6.git.orig/mm/shmem.c
>>>> +++ linux-2.6.git/mm/shmem.c
>>>> @@ -883,16 +883,20 @@ redirty:
>>>>  
>>>>  #ifdef CONFIG_NUMA
>>>>  #ifdef CONFIG_TMPFS
>>>> -static void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
>>>> +static int shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
>>>>  {
>>>>  	char buffer[64];
>>>> +	int ret;
>>>>  
>>>>  	if (!mpol || mpol->mode == MPOL_DEFAULT)
>>>> -		return;		/* show nothing */
>>>> +		return 0;	/* show nothing */
>>>>  
>>>> -	mpol_to_str(buffer, sizeof(buffer), mpol);
>>>> +	ret = mpol_to_str(buffer, sizeof(buffer), mpol);
>>>> +	if (ret < 0)
>>>> +		return ret;
>>>>  
>>>>  	seq_printf(seq, ",mpol=%s", buffer);
>>>> +	return 0;
>>>>  }
>>>>  
>>>>  static struct mempolicy *shmem_get_sbmpol(struct shmem_sb_info *sbinfo)
>>>> @@ -951,9 +955,7 @@ static struct page *shmem_alloc_page(gfp
>>>>  }
>>>>  #else /* !CONFIG_NUMA */
>>>>  #ifdef CONFIG_TMPFS
>>>> -static inline void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
>>>> -{
>>>> -}
>>>> +static inline int shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol) { return 0; }
>>>>  #endif /* CONFIG_TMPFS */
>>>>  
>>>>  static inline struct page *shmem_swapin(swp_entry_t swap, gfp_t gfp,
>>>> @@ -2577,8 +2579,7 @@ static int shmem_show_options(struct seq
>>>>  	if (!gid_eq(sbinfo->gid, GLOBAL_ROOT_GID))
>>>>  		seq_printf(seq, ",gid=%u",
>>>>  				from_kgid_munged(&init_user_ns, sbinfo->gid));
>>>> -	shmem_show_mpol(seq, sbinfo->mpol);
>>>> -	return 0;
>>>> +	return shmem_show_mpol(seq, sbinfo->mpol);
>>>>  }
>>>>  #endif /* CONFIG_TMPFS */
>>>>  
>>>>
>>>>

Oh, you have done, sorry.

>>>
>>>
>>
>>
> 
> 


-- 
Chen Gang

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