Messages in this thread | | | Date | Fri, 03 Aug 2012 10:41:34 +0200 | From | Jens Axboe <> | Subject | Re: [PATCH] block: Don't use static to define "void *p" in show_partition_start(). |
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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 <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)
Huh, that looks like a clear bug. I've applied it, thanks.
-- Jens Axboe
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