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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 <majianpeng@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
hifive-unleashed-5.1
Jianpeng Ma 2012-08-03 10:42:00 +02:00 committed by Jens Axboe
parent 85b9f66a41
commit 0676806707
1 changed files with 1 additions and 1 deletions
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2
block/genhd.c
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@ -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)