Re: [patch -mm] mm, mempolicy: silence gcc warning

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

(11/25/2013 3:31 PM), Andrew Morton wrote:
> On Sat, 23 Nov 2013 15:49:08 -0500 KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:
> 
>>>> --- a/mm/mempolicy.c
>>>> +++ b/mm/mempolicy.c
>>>> @@ -2950,7 +2950,7 @@ void mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
>>>>               return;
>>>>       }
>>>>
>>>> -     p += snprintf(p, maxlen, policy_modes[mode]);
>>>> +     p += snprintf(p, maxlen, "%s", policy_modes[mode]);
>>>>
>>>>       if (flags & MPOL_MODE_FLAGS) {
>>>>               p += snprintf(p, buffer + maxlen - p, "=");
>>>
>>> mutter.  There are no '%'s in policy_modes[].  Maybe we should only do
>>> this #ifdef CONFIG_KEES.
>>>
>>> mpol_to_str() would be simpler (and slower) if it was switched to use
>>> strncat().
>>
>> IMHO, you should queue this patch. mpol_to_str() is not fast path at all and
>> I don't want worry about false positive warning.
> 
> Yup, it's in mainline.

Thanks.

> 
>>> It worries me that the CONFIG_NUMA=n version of mpol_to_str() doesn't
>>> stick a '\0' into *buffer.  Hopefully it never gets called...
>>
>> Don't worry. It never happens. Currently, all of caller depend on CONFIG_NUMA.
>> However it would be nice if CONFIG_NUMA=n version of mpol_to_str() is
>> implemented
>> more carefully. I don't know who's mistake.
> 
> Put a BUG() in there?

I think this is enough. What do you think?


commit 5691f7f336c511d39fc05821d204a8f7ba18c0cf
Author: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Date:   Mon Nov 25 18:38:25 2013 -0500

    mempolicy: implement mpol_to_str() fallback implementation when !CONFIG_NUMA

    Andrew Morton pointed out mpol_to_str() has no fallback implementation
    for !CONFIG_NUMA and it could be dangerous because callers might assume
    buffer is filled zero terminated string. Fortunately there is no such
    caller. But it would be nice to provide default safe implementation.

    Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>

diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
index 9fe426b..eee0597 100644
--- a/include/linux/mempolicy.h
+++ b/include/linux/mempolicy.h
@@ -309,6 +309,8 @@ static inline int mpol_parse_str(char *str, struct mempolicy **mpol)

 static inline void mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
 {
+	strncpy(buffer, "default", maxlen-1);
+	buffer[maxlen-1] = '\0';
 }

 static inline int mpol_misplaced(struct page *page, struct vm_area_struct *vma,




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