Re: possible deadlock in generic_file_write_iter (2)

[Byungchul Park]

On 12/8/2017 2:07 AM, Dmitry Vyukov wrote:
> On Wed, Dec 6, 2017 at 6:05 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?
> >
> > Hello Dmitry,
> >
> > Yes, it's new one making lockdep track wait_for_completion() as well.
> >
> > And we should enable crossrelease_fullstack if you don't care system
> > slowdown but testing.
>
> I've enabled CONFIG_BOOTPARAM_LOCKDEP_CROSSRELEASE_FULLSTACK. It
> should have the same effect, right?

Sure.

--
Thanks,
Byungchul