Re: possible deadlock in generic_file_write_iter (2)

[Dmitry Vyukov]

On Tue, Dec 5, 2017 at 5:58 AM, Byungchul Park <byungchul.park@xxxxxxx> wrote:
> On 12/4/2017 5:33 PM, Jan Kara wrote:
>>
>> Hello,
>>
>> adding Peter and Byungchul to CC since the lockdep report just looks
>> strange and cross-release seems to be involved. Guys, how did #5 get into
>> the lock chain and what does put_ucounts() have to do with sb_writers
>> there? Thanks!
>
>
> Hello Jan,
>
> In order to get full stack of #5, we have to pass a boot param,
> "crossrelease_fullstack", to the kernel. Now that it only informs
> put_ucounts() in the call trace, it's hard to find out what exactly
> happened at that time, but I can tell #5 shows:
>
> When acquire(sb_writers) in put_ucounts(), it was on the way to
> complete((completion)&req.done) of wait_for_completion() in
> devtmpfs_create_node().
>
> If acquire(sb_writers) in put_ucounts() is stuck, then
> wait_for_completion() in devtmpfs_create_node() would be also
> stuck, since complete() being in the context of acquire(sb_writers)
> cannot be called.
>
> This is why cross-release added the lock chain.

Hi,

What is cross-release? Is it something new? Should we always enable
crossrelease_fullstack during testing?

Thanks