[alsa-devel] INFO: rcu detected stall in io_playback_transfer

[Tetsuo Handa]

Dmitry Vyukov wrote:
> Takashi has already fixed this. See this thread:
> https://groups.google.com/forum/#!searchin/syzkaller-bugs/%22INFO$3A$20rcu$20detected$20stall$20in$20snd_pcm_oss_write3$20(2)%22%7Csort:date/syzkaller-bugs/D2xWV7WTRDk/sCw_gImmCAAJ

Yes, I noticed it just before I post this. But the reason I posted this anyway
is that I feel that there is some other bug revealed by this reproducer.
How can Takashi' patch explain my observation (with linux-next-20180406) ?

/* Hits the stall */
int main(int argc, char *argv[])
{
	const int fd = open("/dev/dsp1", O_RDWR);
	int frag = (0 << 16) | 0;
	char buf[48] = { };
	unshare(CLONE_NEWNS);
	ioctl(fd, SNDCTL_DSP_SETFRAGMENT, &frag);
	write(fd, buf, sizeof(buf));
	return 0;
}

/* Does not hit the stall */
int main(int argc, char *argv[])
{
	const int fd = open("/dev/dsp1", O_RDWR);
	int frag = (0 << 16) | 0;
	char buf[48] = { };
	ioctl(fd, SNDCTL_DSP_SETFRAGMENT, &frag);
	write(fd, buf, sizeof(buf));
	return 0;
}

/* Does not hit the stall */
int main(int argc, char *argv[])
{
	const int fd = open("/dev/dsp1", O_RDWR);
	int frag = (0 << 16) | 0;
	char buf[48] = { };
	unshare(CLONE_NEWNS);
	ioctl(fd, SNDCTL_DSP_SETFRAGMENT, &frag);
	write(fd, buf, sizeof(buf));
	close(fd);
	return 0;
}