linux/block
Jianpeng Ma 0676806707 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>
2012-08-03 10:42:00 +02:00
..
partitions s390/dasd: re-prioritize partition detection message 2012-05-16 14:42:51 +02:00
Kconfig move fs/partitions to block/ 2012-01-03 22:54:06 -05:00
Kconfig.iosched blkcg: make CONFIG_BLK_CGROUP bool 2012-03-06 21:27:21 +01:00
Makefile separate partition format handling from generic code 2012-01-03 22:54:06 -05:00
blk-cgroup.c blkcg: implement per-blkg request allocation 2012-06-26 18:42:49 -04:00
blk-cgroup.h blkcg: implement per-blkg request allocation 2012-06-26 18:42:49 -04:00
blk-core.c blk: pass from_schedule to non-request unplug functions. 2012-07-31 09:08:15 +02:00
blk-exec.c [SCSI] block: Fix blk_execute_rq_nowait() dead queue handling 2012-07-20 08:58:39 +01:00
blk-flush.c blk-flush: move the queue kick into 2011-10-24 16:24:31 +02:00
blk-integrity.c block: add export.h to files using EXPORT_SYMBOL/THIS_MODULE macros 2011-10-31 19:31:12 -04:00
blk-ioc.c block: uninitialized ioc->nr_tasks triggers WARN_ON 2012-08-01 12:17:27 +02:00
blk-iopoll.c tree-wide: fix assorted typos all over the place 2009-12-04 15:39:55 +01:00
blk-lib.c block: split discard into aligned requests 2012-08-02 09:48:50 +02:00
blk-map.c block: re-use existing 'reading' variable instead of checking direction again 2011-12-21 15:27:24 +01:00
blk-merge.c block: Add blk_bio_map_sg() helper 2012-08-02 23:42:04 +02:00
blk-settings.c block: do not artificially constrain max_sectors for stacking drivers 2012-08-01 10:44:28 +02:00
blk-softirq.c sched, block: Unify cache detection 2012-01-27 13:28:48 +01:00
blk-sysfs.c blkcg: implement per-blkg request allocation 2012-06-26 18:42:49 -04:00
blk-tag.c block: fix blk_queue_end_tag() 2011-12-29 09:16:28 +01:00
blk-throttle.c block: allocate io_context upfront 2012-06-25 11:53:50 +02:00
blk-timeout.c block: Drop dead function blk_abort_queue() 2012-06-15 08:46:23 +02:00
blk.h block: remove dead func declaration 2012-08-01 12:25:54 +02:00
bsg-lib.c block: drop custom queue draining used by scsi_transport_{iscsi|fc} 2012-06-25 11:53:48 +02:00
bsg.c bsg: fix sysfs link remove warning 2012-02-08 20:02:03 +01:00
cfq-iosched.c block: blkcg_policy_cfq shouldn't be used if !CONFIG_CFQ_GROUP_IOSCHED 2012-06-04 10:02:29 +02:00
compat_ioctl.c block: Add BLKROTATIONAL ioctl 2012-01-11 16:29:31 +01:00
deadline-iosched.c elevator: make elevator_init_fn() return 0/-errno 2012-03-06 21:27:21 +01:00
elevator.c blkcg: implement per-queue policy activation 2012-04-20 10:06:06 +02:00
genhd.c block: Don't use static to define "void *p" in show_partition_start() 2012-08-03 10:42:00 +02:00
ioctl.c block: add partition resize function to blkpg ioctl 2012-08-01 12:24:18 +02:00
noop-iosched.c elevator: make elevator_init_fn() return 0/-errno 2012-03-06 21:27:21 +01:00
partition-generic.c block: add partition resize function to blkpg ioctl 2012-08-01 12:24:18 +02:00
scsi_ioctl.c scsi: Silence unnecessary warnings about ioctl to partition 2012-06-15 12:52:46 +02:00