On 05/18/2016 12:32 PM, Nicolai Stange wrote:
> Sasha Levin <sasha.le...@oracle.com> writes:
>
>> 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?
>
> Could you try the patch below? I stared at the new full_proxy_open() for
> a while now and had to recognize the fact that if the original real_fops'
> ->open() fails, then its owning module's reference won't ever get
> dropped :(
>
> diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
> index 6eb58a8..2e663d4 100644
> --- a/fs/debugfs/file.c
> +++ b/fs/debugfs/file.c
> @@ -263,10 +263,14 @@ static int full_proxy_open(struct inode *inode, struct
> file *filp)
> if (real_fops->open) {
> r = real_fops->open(inode, filp);
>
> - if (filp->f_op != proxy_fops) {
> + if (r) {
> + replace_fops(filp, d_inode(dentry)->i_fop);
> + goto free_proxy;
> + } else if (filp->f_op != proxy_fops) {
> /* No protection against file removal anymore. */
> WARN(1, "debugfs file owner replaced proxy fops: %pd",
> dentry);
> + replace_fops(filp, d_inode(dentry)->i_fop);
> goto free_proxy;
> }
> }
>
>
> I don't see directly how this could lead to lockups, but I think it's
> better to rule out the obvious before inserting more or less random
> printks...
>
> Thank you very much again,
Nope, that didn't do the trick.
Thanks,
Sasha
