On 05/18/2016 12:05 PM, Greg Kroah-Hartman wrote:
> On Wed, May 18, 2016 at 11:18:16AM -0400, Sasha Levin wrote:
>> On 05/18/2016 11:01 AM, Nicolai Stange wrote:
>>> Thanks a million for reporting!
>>>
>>> 1.) Do you have lockdep enabled?
>>
>> Yup, nothing there.
>>
>>> 2.) Does this happen before or after userspace init has been spawned,
>>> i.e. does the lockup happen at debugfs file creation time or
>>> possibly at usage time?
>>
>> So I looked closer, and it seems to happen after starting syzkaller, which
>> as far as I know tries to open many different debugfs files.
>>
>> Is there debug code I can add it that'll help us figure out what's up?
>
> Trying to figure out _which_ debugfs file is causing this would be
> great, if at all possible. strace?
What seems to be failing is syzkaller's attempt to mmap the coverage
debugfs file. So this isn't actually a kernel deadlock but syzkaller
misbehaves when that scenario happens.
Either way, it only fails to mmap with that commit that I've pointed
out.
th->cover_fd = open("/sys/kernel/debug/kcov", O_RDWR);
if (th->cover_fd == -1)
fail("open of /sys/kernel/debug/kcov failed");
if (ioctl(th->cover_fd, KCOV_INIT_TRACE, kCoverSize))
fail("cover enable write failed");
th->cover_data = (uintptr_t*)mmap(NULL, kCoverSize *
sizeof(th->cover_data[0]), PROT_READ | PROT_WRITE, MAP_SHARED, th->cover_fd, 0);
if ((void*)th->cover_data == MAP_FAILED)
fail("cover mmap failed");
And it's the mmap() that fails with -ENODEV.
Thanks,
Sasha
