netdev - Re: ARM board lockups/hangs triggered by locks and mutexes

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Date: Fri, 4 Aug 2023 13:07:41 +0200
From: Rafał Miłecki <zajec5@...il.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
 Will Deacon <will@...nel.org>, Waiman Long <longman@...hat.com>,
 Boqun Feng <boqun.feng@...il.com>, Russell King <linux@...linux.org.uk>,
 Daniel Lezcano <daniel.lezcano@...aro.org>,
 Thomas Gleixner <tglx@...utronix.de>, Florian Fainelli
 <f.fainelli@...il.com>, linux-clk@...r.kernel.org,
 "linux-arm-kernel@...ts.infradead.org"
 <linux-arm-kernel@...ts.infradead.org>,
 Network Development <netdev@...r.kernel.org>,
 Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc: OpenWrt Development List <openwrt-devel@...ts.openwrt.org>,
 bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>
Subject: Re: ARM board lockups/hangs triggered by locks and mutexes

On 2.08.2023 00:10, Rafał Miłecki wrote:
> Unfortunately enabling *any* of following options:
> CONFIG_DEBUG_RT_MUTEXES=y
> CONFIG_DEBUG_SPINLOCK=y
> CONFIG_DEBUG_MUTEXES=y
> seems to make locksup/hangs go away. I tried for few hours.

I decided to find out why enabling CONFIG_DEBUG_MUTEXES "fixes" kernel /
device stability for me. I tried enabling manually code that normally
hides behind the #ifdev CONFIG_DEBUG_MUTEXES.

Attached to this e-mail is a small patch that is enough to make my
kernel stable (mutex-fix-bcm53573.diff).

#####

It's not what's the most interesting thought. What really doesn't make
sense anymore is that below diff (on top of attached one) brings back
hangs/lockups.

I triple checked that. Dropping a single unused function breaks kernel /
device stability on BCM53573!

AFAIK the only thing below diff actually affects is location of symbols
(I actually verified that by comparing System.map before and after -
over 22'000 of relocated symbols).

Can some unfortunate location of symbols cause those hangs/lockups?


diff --git a/kernel/locking/mutex-debug.c b/kernel/locking/mutex-debug.c
index 4fe40910f..c440222a4 100644
--- a/kernel/locking/mutex-debug.c
+++ b/kernel/locking/mutex-debug.c
@@ -34,6 +34,8 @@ void debug_mutex_lock_common(struct mutex *lock, struct mutex_waiter *waiter)
  	INIT_LIST_HEAD(&waiter->list);
  }

+/* Dropping below function brings back hangs/lockups & reboots */
+#if 0
  void debug_mutex_wake_waiter(struct mutex *lock, struct mutex_waiter *waiter)
  {
  	lockdep_assert_held(&lock->wait_lock);
@@ -41,6 +43,7 @@ void debug_mutex_wake_waiter(struct mutex *lock, struct mutex_waiter *waiter)
  	DEBUG_LOCKS_WARN_ON(waiter->magic != waiter);
  	DEBUG_LOCKS_WARN_ON(list_empty(&waiter->list));
  }
+#endif

  void debug_mutex_free_waiter(struct mutex_waiter *waiter)
  {

View attachment "mutex-fix-bcm53573.diff" of type "text/x-patch" (2238 bytes)