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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Oleksandr Natalenko <oleksandr@natalenko.name>,
        bugzilla-daemon@bugzilla.kernel.org
Cc:     jdelvare@suse.de, wsa@kernel.org, benjamin.tissoires@redhat.com,
        rui.zhang@intel.com, linux-i2c@vger.kernel.org,
        linux-kernel@vger.kernel.org, Marc Zyngier <maz@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Carlos Jimenez <javashin1986@gmail.com>
Subject: Re: [Bug 202453] TRACE irq/18-i801_smb Tainted when enabled threadirqs in kernel commandline.
In-Reply-To: <20201204201930.vtvitsq6xcftjj3o@spock.localdomain>
References: <bug-202453-19117@https.bugzilla.kernel.org/> <bug-202453-19117-0k1QQBMPTi@https.bugzilla.kernel.org/> <20201204201930.vtvitsq6xcftjj3o@spock.localdomain>
Date:   Sat, 05 Dec 2020 17:19:18 +0100
Message-ID: <87zh2s8buh.fsf@nanos.tec.linutronix.de>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

On Fri, Dec 04 2020 at 21:19, Oleksandr Natalenko wrote:
> On Thu, Dec 03, 2020 at 07:04:00PM +0000, bugzilla-daemon@bugzilla.kernel.org wrote:
>>    2) Have a wrapper around handle_generic_irq() which ensures that
>>       interrupts are disabled before invoking it.

> The question is whether it's guaranteed under all circumstances
> including forced irq threading. The i801 driver has assumptions about
> this, so I wouldn't be surprised if there are more.

Assuming that a final answer might take some time, the below which
implements #2 will make it at least work for now.

Thanks,

        tglx
---
Subject: genirq, i2c: Provide and use generic_dispatch_irq()
From: Thomas Gleixner <tglx@linutronix.de>
Date: Thu, 03 Dec 2020 19:12:24 +0100

Carlos reported that on his system booting with 'threadirqs' on the command
line result in the following warning:

irq 31 handler irq_default_primary_handler+0x0/0x10 enabled interrupts
WARNING: CPU: 2 PID: 989 at kernel/irq/handle.c:153 __handle_irq_event_percpu+0x19f/0x1b0

The reason is in the i2c stack:

    i801_isr()
      i801_host_notify_isr()
        i2c_handle_smbus_host_notify()
          generic_handle_irq()

and that explodes with forced interrupt threading because it's called with
interrupts enabled.

It would be possible to set IRQF_NO_THREAD on the i801 interrupt to exclude
it from force threading, but that would break on RT and require a larger
update.

It's also unclear whether there are other drivers which can reach that code
path via i2c_slave_host_notify_cb(). As there are enough i2c drivers which
use threaded interrupt handlers by default it seems not completely
impossible that this can happen even without force threaded interrupts.

For a quick fix provide a wrapper around generic_handle_irq() which has a
local_irq_save/restore() around the invocation and use it in the i2c code.

Reported-by: Carlos Jimenez <javashin1986@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=202453
---
 drivers/i2c/i2c-core-base.c |    2 +-
 include/linux/irqdesc.h     |    1 +
 kernel/irq/irqdesc.c        |   20 ++++++++++++++++++++
 3 files changed, 22 insertions(+), 1 deletion(-)

--- a/drivers/i2c/i2c-core-base.c
+++ b/drivers/i2c/i2c-core-base.c
@@ -1385,7 +1385,7 @@ int i2c_handle_smbus_host_notify(struct
 	if (irq <= 0)
 		return -ENXIO;
 
-	generic_handle_irq(irq);
+	generic_dispatch_irq(irq);
 
 	return 0;
 }
--- a/include/linux/irqdesc.h
+++ b/include/linux/irqdesc.h
@@ -153,6 +153,7 @@ static inline void generic_handle_irq_de
 }
 
 int generic_handle_irq(unsigned int irq);
+int generic_dispatch_irq(unsigned int irq);
 
 #ifdef CONFIG_HANDLE_DOMAIN_IRQ
 /*
--- a/kernel/irq/irqdesc.c
+++ b/kernel/irq/irqdesc.c
@@ -652,6 +652,26 @@ int generic_handle_irq(unsigned int irq)
 }
 EXPORT_SYMBOL_GPL(generic_handle_irq);
 
+/**
+ * generic_dispatch_irq - Dispatch an interrupt from an interrupt handler
+ * @irq:	The irq number to handle
+ *
+ * A wrapper around generic_handle_irq() which ensures that interrupts are
+ * disabled when the primary handler of the dispatched irq is invoked.
+ * This is useful for interrupt handlers with dispatching to be safe for
+ * the forced threaded case.
+ */
+int generic_dispatch_irq(unsigned int irq)
+{
+	unsigned long flags;
+	int ret;
+
+	local_irq_save(&flags);
+	ret = generic_handle_irq(irq);
+	local_irq_restore(&flags);
+	return ret;
+}
+
 #ifdef CONFIG_HANDLE_DOMAIN_IRQ
 /**
  * __handle_domain_irq - Invoke the handler for a HW irq belonging to a domain