On 3/12/24 14:15, Paul E. McKenney wrote:
On Tue, Mar 12, 2024 at 10:01:00PM +0100, Frederic Weisbecker wrote:
Le Tue, Mar 12, 2024 at 01:32:03PM -0700, Florian Fainelli a écrit :
Hi Boqun,
On 3/8/24 09:15, Boqun Feng wrote:
Hi Linus,
Please pull this for the RCU changes of v6.9:
The following changes since commit 41bccc98fb7931d63d03f326a746ac4d429c1dd3:
Linux 6.8-rc2 (2024-01-28 17:01:12 -0800)
are available in the Git repository at:
git://git.kernel.org/pub/scm/linux/kernel/git/boqun/linux.git tags/rcu.next.v6.9
for you to fetch changes up to 3add00be5fe5810d7aa5ec3af8b6a245ef33144b:
Merge branches 'rcu-doc.2024.02.14a', 'rcu-nocb.2024.02.14a', 'rcu-exp.2024.02.14a', 'rcu-tasks.2024.02.26a' and 'rcu-misc.2024.02.14a' into rcu.2024.02.26a (2024-02-26 17:37:25 -0800)
Two merge conflicts were detected by linux-next:
* https://lore.kernel.org/lkml/20240226135745.12ac854d@xxxxxxxxxxxxxxxx/
* https://lore.kernel.org/lkml/20240227125522.2bdbe6be@xxxxxxxxxxxxxxxx/
These conflict resolutions from linux-next look good to me, plus I made
my own resolutions at branch merge/rcu.2024.02.27a for your reference.
Some highlights of the changes:
* Eliminates deadlocks involving do_exit() and RCU tasks, by Paul:
Instead of SRCU read side critical sections, now a percpu list is used
in do_exit() for scaning yet-to-exit tasks.
* Fixes a deadlock due to the dependency between workqueue and RCU
expedited grace period, reported by Anna-Maria Behnsen and Thomas
Gleixner and fixed by Frederic: Now RCU expedited always uses its own
kthread worker instead of a workqueue.
At least one device in my test farm (ARM 32-bit) has consistently shown a
very long boot, and some others are intermittently affected. This
consistently looks like this on most of my devices:
[ 2.450351] bcmgenet f0480000.ethernet: GENET 5.0 EPHY: 0x0000
[ 2.547562] ata1: SATA link down (SStatus 0 SControl 300)
[ 162.107264] unimac-mdio unimac-mdio.0: Broadcom UniMAC MDIO bus
this gets flagged by my boot script as a boot failure since we exceeded the
30 seconds timeout given to boot a kernel to a prompt.
It has been somewhat difficult to get a reliable bisection going on, but
what I am sure of is that e5a3878c947ceef7b6ab68fdc093f3848059842c~1 does
not expose the problem for 10 consecutive boots, while I *might* see it at
e5a3878c947ceef7b6ab68fdc093f3848059842c and beyond.
Any clues what is going on here?
I understand it doesn't reliably reproduce. But is there any chance you could
test that alone?
0bb11a372fc8 (rcu-tasks: Maintain real-time response in rcu_tasks_postscan())
And if it reproduces there try a bisection?
git bisect bad 0bb11a372fc8d7006b4d0f42a2882939747bdbff
git bisect good 41bccc98fb7931d63d03f326a746ac4d429c1dd3
Good point!
Is this kernel built with CONFIG_PREEMPT_RT=y and CONFIG_TASKS_RCU=y?
Either way, is there also a large number of tasks exiting at this point
during boot?
Neither options are enabled, and this is still during boot, so there is
not any user-space tasks being running yet, I cannot think of too many
reasons why this would fail, and there is no driver on the probe
deferral list that I can see.
--
Florian
