linux-kernel - Re: Fwd: RCU indicates stalls with iwlwifi, causing boot failures

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Date:   Fri, 1 Sep 2023 19:07:19 -0700
From:   Ben Greear <greearb@...delatech.com>
To:     Bagas Sanjaya <bagasdotme@...il.com>,
        Lai Jiangshan <laijs@...ux.alibaba.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Gregory Greenman <gregory.greenman@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Networking <netdev@...r.kernel.org>,
        Linux Wireless <linux-wireless@...r.kernel.org>,
        Linux RCU <rcu@...r.kernel.org>
Subject: Re: Fwd: RCU indicates stalls with iwlwifi, causing boot failures

On 9/1/23 5:29 PM, Bagas Sanjaya wrote:
> Hi,
> 
> I notice a bug report on Bugzilla [1]. Quoting from it:

Try booting with pcie=noaer ?

That fixes only known iwlwifi bug we have found in 6.5, but we are also using mostly
backports iwlwifi driver...

Thanks,
Ben

> 
>> 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
> 


-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com