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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 <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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