2012-08-03 05:06:31

by majianpeng

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

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 <[email protected]>
---
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
????{.n?+???????+%?????ݶ??w??{.n?+????{??G?????{ay?ʇڙ?,j??f???h?????????z_??(?階?ݢj"???m??????G????????????&???~???iO???z??v?^?m????????????I?

2012-08-03 08:41:53

by Jens Axboe

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

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 <[email protected]>
> ---
> 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

2012-08-12 15:45:40

by Michael Tokarev

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

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

2012-08-13 00:38:37

by majianpeng

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

On 2012-08-12 23:45 Michael Tokarev <[email protected]> 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.????{.n?+???????+%?????ݶ??w??{.n?+????{??G?????{ay?ʇڙ?,j??f???h?????????z_??(?階?ݢj"???m??????G????????????&???~???iO???z??v?^?m????????????I?