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Date:   Sat, 2 Sep 2023 07:29:55 +0700
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To:     Lai Jiangshan <laijs@linux.alibaba.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Gregory Greenman <gregory.greenman@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Linux Networking <netdev@vger.kernel.org>,
        Linux Wireless <linux-wireless@vger.kernel.org>,
        Linux RCU <rcu@vger.kernel.org>
From:   Bagas Sanjaya <bagasdotme@gmail.com>
Subject: Fwd: RCU indicates stalls with iwlwifi, causing boot failures
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Hi,

I notice a bug report on Bugzilla [1]. Quoting from it:

> I'm seeing RCU warnings in Linus's current tree (like 87dfd85c38923acd9517e8df4afc908565df0961) that come from RCU:
> 
> WARNING: CPU: 0 PID: 0 at kernel/rcu/tree_exp.h:787 rcu_exp_handler+0x35/0xe0
> 
> But they *ONLY* occur on a system with a newer iwlwifi device:
> 
> aa:00.0 Network controller: Intel Corporation Wi-Fi 6 AX210/AX211/AX411 160MHz (rev 1a)
> 
> and never in a VM or on an older device (like an 8260).  During a bisect the only seem to occur with the "83" version of the firmware.
> 
> iwlwifi 0000:aa:00.0: loaded firmware version 83.e8f84e98.0 ty-a0-gf-a0-83.ucode op_mode iwlmvm
> 
> The first warning gets spit out within a millisecond of the last printk() from the iwlwifi driver.  They eventually result in a big spew of RCU messages like this:
> 
> [   27.124796] rcu: INFO: rcu_preempt detected expedited stalls on CPUs/tasks: { 0-...D } 125 jiffies s: 193 root: 0x1/.
> [   27.126466] rcu: blocking rcu_node structures (internal RCU debug):
> [   27.128114] Sending NMI from CPU 3 to CPUs 0:
> [   27.128122] NMI backtrace for cpu 0 skipped: idling at intel_idle+0x5f/0xb0
> [   27.159757] loop30: detected capacity change from 0 to 8
> [   27.204967] rcu: INFO: rcu_preempt detected expedited stalls on CPUs/tasks: { 0-...D } 145 jiffies s: 193 root: 0x1/.
> [   27.206353] rcu: blocking rcu_node structures (internal RCU debug):
> [   27.207751] Sending NMI from CPU 3 to CPUs 0:
> [   27.207825] NMI backtrace for cpu 0 skipped: idling at intel_idle+0x5f/0xb0
> 
> I usually see them at boot.  In that case, they usually hang the system and keep it from booting.  I've also encountered them at reboots and also seen them *not* be fatal at boot.  I suspect it has to do with which CPU gets wedged.

See Bugzilla for the full thread and attached full dmesg output.

Thanks.

[1]: https://bugzilla.kernel.org/show_bug.cgi?id=217856

-- 
An old man doll... just what I always wanted! - Clara