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
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