Originally this problem was reproduced by the following scripts:
# dd if=/dev/zero of=data bs=1M count=50
# losetup /dev/loop1 data
# i=1
# while [ 1 ]
do
mkfs.btrfs -fK /dev/loop1 >& /dev/null || exit 1
i++
echo "loop $i"
done
Further, a easy way to trigger this problem is by running the followng c
codes repeatedly:
int main(int argc, char **argv)
{
int fd = open(argv[1], O_RDWR | O_EXCL);
if (fd < 0) {
perror("fail to open");
exit(1);
}
close(fd);
return 0;
}
here @argv[1] needs a btrfs block device.
So the problem is RW opening would trigger udev event which will call
btrfs_scan_one_device()
In btrfs_scan_one_device(), it would open the block device with EXCL
flag...meanwhile if another
program try to open that device with O_EXCL, it would fail with EBUSY....
I don't know whether this is a serious problem, now there are two places
in btrfs-progs that is
trying to open device with O_EXCL:
1. in utils.c: test_dev_for_mkfs()
2. in disk-io.c: __open_ctree_fd()
Any ideas on this? maybe we can remove @EXCL flag from btrfs-progs?
Thanks,
Wang
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