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

[Chen Gang <gang.chen@asianux.com>]

Sorry for reply multiple times to bother many members.

It seems, I am tired, and need have a rest today. :-(


On 08/20/2013 04:13 PM, Chen Gang F T wrote:
> 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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