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
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