Re: [GIT PULL] Networking for v6.9
From: Linus Torvalds
Date: Tue Mar 12 2024 - 17:11:54 EST
On Tue, 12 Mar 2024 at 13:47, Jakub Kicinski <kuba@xxxxxxxxxx> wrote:
>
> With your tree as of 65d287c7eb1d it gets to prompt but dies soon after
> when prod services kick in (dunno what rpm Kdump does but says iocost
> so adding Tejun):
Both of your traces are timers that seem to either lock up in ioc_now():
https://lore.kernel.org/all/20240312133427.1a744844@xxxxxxxxxx/
and now it looks like ioc_timer_fn():
https://lore.kernel.org/all/20240312134739.248e6bd3@xxxxxxxxxx/
But in neither case does it actually look like it's a lockup on a *lock*.
IOW, the NMI isn't happening on some spin_lock sequence or anything like that.
Yes, ioc_now() could have been looping on the seq read-lock if the
sequence number was odd. But the writers do seem to be done with
interrupts disabled, plus then you wouldn't have this lockup in
ioc_timer_fn, so it's probably not that.
And yes, ioc_timer_fn() does take locks, but again, that doesn't seem
to be where it is hanging.
So it smells like it's an endless loop in ioc_timer_fn() to me, or
perhaps retriggering the timer itself infinitely.
Which would then explain both of those traces (that endless loop would
call ioc_now() as part of it).
The blk-iocost.c code itself hasn't changed, but the timer code has
gone through big changes.
That said, there's a more blk-related change: da4c8c3d0975 ("block:
cache current nsec time in struct blk_plug").
*And* your second dump is from that
period_vtime = now.vnow - ioc->period_at_vtime;
if (WARN_ON_ONCE(!period_vtime)) {
so it smells like the blk-iocost code is just completely confused by
the time caching. Jens?
Jakub, it might be worth seeing if just reverting that commit
da4c8c3d0975 makes the problem go away. Otherwise a bisect might be
needed...
Linus