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

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Date: Fri, 4 Aug 2023 12:24:15 +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:
> Reverting that extra commit from v5.4.238 allows me to run Linux for
> hours again (currently 3 devices x 6 hours and counting). So I need in
> total 10+1 reverts from 5.4 branch to get a stable kernel.

I switched back to OpenWrt's kernel 5.4 and applied all those reverts I
found. Nothing. I was still getting hangs / lockups + reboots.

After more bisecting and I found out it's because OpenWrt backported
commit ad9b10d1eaad ("mtd: core: introduce of support for dynamic
partitions"):
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ad9b10d1eaada169bd764abcab58f08538877e26

It didn't make any sense to me. That patch does nothing on my device and
its code is only executed when booting.

It makes even less sense to me. Why such changes that should not affect
anything actually break stability for BCM53573?

I narrowed above patch even furher. It's actually enough to apply below
diff to break kernel stability:

diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index f69c5b94e..f10dd3af1 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -590,6 +590,25 @@ static int mtd_nvmem_add(struct mtd_info *mtd)
  	return 0;
  }

+static void mtd_check_of_node(struct mtd_info *mtd)
+{
+	struct device_node *partitions, *parent_dn;
+	struct mtd_info *parent;
+
+	/* Check if MTD already has a device node */
+	if (dev_of_node(&mtd->dev))
+		return;
+
+	/* Check if a partitions node exist */
+	parent = mtd_get_master(mtd);
+	parent_dn = dev_of_node(&parent->dev);
+	pr_info("[%s] mtd->name:%s parent_dn:%pOF\n", __func__, mtd->name, parent_dn);
+	if (!parent_dn)
+		return;
+
+	of_node_put(parent_dn);
+}
+
  /**
   *	add_mtd_device - register an MTD device
   *	@mtd: pointer to new MTD device info structure
@@ -673,6 +692,7 @@ int add_mtd_device(struct mtd_info *mtd)
  	mtd->dev.devt = MTD_DEVT(i);
  	dev_set_name(&mtd->dev, "mtd%d", i);
  	dev_set_drvdata(&mtd->dev, mtd);
+	mtd_check_of_node(mtd);
  	of_node_get(mtd_get_of_node(mtd));
  	error = device_register(&mtd->dev);
  	if (error) {