[PATCH] block: Don't use static to define "void *p" in show_partition_start().

[PATCH] block: Don't use static to define "void *p" in show_partition_start().

[majianpeng]

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I met a odd prblem:read /proc/partitions may return zero.

I wrote a file test.c:
int main()
{
	char buff[4096];
	int ret;
	int fd;
	printf("pid=%d\n",getpid());
	while (1) {
		fd = open("/proc/partitions", O_RDONLY);
		if (fd < 0) {
			printf("open error %s\n", strerror(errno));
			return 0;
		}
		ret = read(fd, buff, 4096);
		if (ret <= 0)
			printf("ret=%d, %s, %ld\n", ret,
				strerror(errno), lseek(fd,0,SEEK_CUR));
		close(fd);
	}
	exit(0);
}

You can reproduce by:
1:while true;do cat /proc/partitions > /dev/null ;done
2:./test

I reviewed the code and found:
>>static void *show_partition_start(struct seq_file *seqf, loff_t *pos)
>>{
>>	static void *p;

>>	p = disk_seqf_start(seqf, pos);
>>	if (!IS_ERR_OR_NULL(p) && !*pos)
>>		seq_puts(seqf, "major minor  #blocks  name\n\n");
>>	return p;
>>}
		test								cat /proc/partitions
	p = disk_seqf_start()(Not NULL)
									p = disk_seqf_start()(NULL because pos)
	if (!IS_ERR_OR_NULL(p) && !*pos)

Signed-off-by: Jianpeng Ma <majianpeng@gmail.com>
---
 block/genhd.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block/genhd.c b/block/genhd.c
index cac7366..d839723 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -835,7 +835,7 @@ static void disk_seqf_stop(struct seq_file *seqf, void *v)
 
 static void *show_partition_start(struct seq_file *seqf, loff_t *pos)
 {
-	static void *p;
+	void *p;
 
 	p = disk_seqf_start(seqf, pos);
 	if (!IS_ERR_OR_NULL(p) && !*pos)
-- 
1.7.9.5
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Re: [PATCH] block: Don't use static to define "void *p" in show_partition_start().

[Jens Axboe]

On 08/03/2012 07:07 AM, majianpeng wrote:
> I met a odd prblem:read /proc/partitions may return zero.
> 
> I wrote a file test.c:
> int main()
> {
> 	char buff[4096];
> 	int ret;
> 	int fd;
> 	printf("pid=%d\n",getpid());
> 	while (1) {
> 		fd = open("/proc/partitions", O_RDONLY);
> 		if (fd < 0) {
> 			printf("open error %s\n", strerror(errno));
> 			return 0;
> 		}
> 		ret = read(fd, buff, 4096);
> 		if (ret <= 0)
> 			printf("ret=%d, %s, %ld\n", ret,
> 				strerror(errno), lseek(fd,0,SEEK_CUR));
> 		close(fd);
> 	}
> 	exit(0);
> }
> 
> You can reproduce by:
> 1:while true;do cat /proc/partitions > /dev/null ;done
> 2:./test
> 
> I reviewed the code and found:
>>> static void *show_partition_start(struct seq_file *seqf, loff_t *pos)
>>> {
>>> 	static void *p;
> 
>>> 	p = disk_seqf_start(seqf, pos);
>>> 	if (!IS_ERR_OR_NULL(p) && !*pos)
>>> 		seq_puts(seqf, "major minor  #blocks  name\n\n");
>>> 	return p;
>>> }
> 		test								cat /proc/partitions
> 	p = disk_seqf_start()(Not NULL)
> 									p = disk_seqf_start()(NULL because pos)
> 	if (!IS_ERR_OR_NULL(p) && !*pos)
> 
> Signed-off-by: Jianpeng Ma <majianpeng@gmail.com>
> ---
>  block/genhd.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/block/genhd.c b/block/genhd.c
> index cac7366..d839723 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -835,7 +835,7 @@ static void disk_seqf_stop(struct seq_file *seqf, void *v)
>  
>  static void *show_partition_start(struct seq_file *seqf, loff_t *pos)
>  {
> -	static void *p;
> +	void *p;
>  
>  	p = disk_seqf_start(seqf, pos);
>  	if (!IS_ERR_OR_NULL(p) && !*pos)

Huh, that looks like a clear bug. I've applied it, thanks.

-- 
Jens Axboe

Re: [PATCH] block: Don't use static to define "void *p" in show_partition_start().

[Michael Tokarev]

On 03.08.2012 12:41, Jens Axboe wrote:
> On 08/03/2012 07:07 AM, majianpeng wrote:
[]
>> diff --git a/block/genhd.c b/block/genhd.c
>> index cac7366..d839723 100644
>> --- a/block/genhd.c
>> +++ b/block/genhd.c
>> @@ -835,7 +835,7 @@ static void disk_seqf_stop(struct seq_file *seqf, void *v)
>>  
>>  static void *show_partition_start(struct seq_file *seqf, loff_t *pos)
>>  {
>> -	static void *p;
>> +	void *p;
>>  
>>  	p = disk_seqf_start(seqf, pos);
>>  	if (!IS_ERR_OR_NULL(p) && !*pos)
> 
> Huh, that looks like a clear bug. I've applied it, thanks.

It also looks like a -stable material, don't you think?

Thanks,

/mjt

Re: Re: [PATCH] block: Don't use static to define "void *p" in show_partition_start().

[Jianpeng Ma]

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On 2012-08-12 23:45 Michael Tokarev <mjt@tls.msk.ru> Wrote:
>On 03.08.2012 12:41, Jens Axboe wrote:
>> On 08/03/2012 07:07 AM, majianpeng wrote:
>[]
>>> diff --git a/block/genhd.c b/block/genhd.c
>>> index cac7366..d839723 100644
>>> --- a/block/genhd.c
>>> +++ b/block/genhd.c
>>> @@ -835,7 +835,7 @@ static void disk_seqf_stop(struct seq_file *seqf, void *v)
>>>  
>>>  static void *show_partition_start(struct seq_file *seqf, loff_t *pos)
>>>  {
>>> -	static void *p;
>>> +	void *p;
>>>  
>>>  	p = disk_seqf_start(seqf, pos);
>>>  	if (!IS_ERR_OR_NULL(p) && !*pos)
>> 
>> Huh, that looks like a clear bug. I've applied it, thanks.
>
>It also looks like a -stable material, don't you think?
>
>Thanks,
>
>/mjt
>
Yes, all kernel before this patach had this problem and should apply this patch.ÿôèº{.nÇ+‰·Ÿ®‰­†+%ŠËÿ±éݶ\x17¥Šwÿº{.nÇ+‰·¥Š{±þG«éÿŠ{ayº\x1dʇڙë,j\a­¢f£¢·hšïêÿ‘êçz_è®\x03(­éšŽŠÝ¢j"ú\x1a¶^[m§ÿÿ¾\a«þG«éÿ¢¸?™¨è­Ú&£ø§~á¶iO•æ¬z·švØ^\x14\x04\x1a¶^[m§ÿÿÃ\fÿ¶ìÿ¢¸?–I¥