linux-kernel - Re: [PATCH v2] PCI: endpoint: pci-epf-test: Fix sleeping function being called from atomic context

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Message-ID: <aOeCWdbdfMpWIKv_@ryzen>
Date: Thu, 9 Oct 2025 11:37:29 +0200
From: Niklas Cassel <cassel@...nel.org>
To: Bhanu Seshu Kumar Valluri <bhanuseshukumar@...il.com>
Cc: mani@...nel.org, kwilczynski@...nel.org, kishon@...nel.org,
	bhelgaas@...gle.com, Frank.Li@....com, dlemoal@...nel.org,
	christian.bruel@...s.st.com, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] PCI: endpoint: pci-epf-test: Fix sleeping function
 being called from atomic context

On Tue, Sep 30, 2025 at 08:08:09AM +0530, Bhanu Seshu Kumar Valluri wrote:
> When Root Complex(RC) triggers a Doorbell MSI interrupt to Endpoint(EP) it triggers a warning
> in the EP. pci_endpoint kselftest target is compiled and used to run the Doorbell test in RC.
> 
> [  474.686193] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:271
> [  474.710934] Call trace:
> [  474.710995]  __might_resched+0x130/0x158
> [  474.711011]  __might_sleep+0x70/0x88
> [  474.711023]  mutex_lock+0x2c/0x80
> [  474.711036]  pci_epc_get_msi+0x78/0xd8
> [  474.711052]  pci_epf_test_raise_irq.isra.0+0x74/0x138
> [  474.711063]  pci_epf_test_doorbell_handler+0x34/0x50
> 
> The BUG arises because the EP's pci_epf_test_doorbell_handler is making an
> indirect call to pci_epc_get_msi, which uses mutex inside, from interrupt context.
> 
> To fix the issue convert hard irq handler to a threaded irq handler to allow it
> to call functions that can sleep during bottom half execution. Register threaded
> irq handler with IRQF_ONESHOT to keep interrupt line disabled until the threaded
> irq handler completes execution.
> 
> Fixes: eff0c286aa91 ("PCI: endpoint: pci-epf-test: Add doorbell test support")
> Signed-off-by: Bhanu Seshu Kumar Valluri <bhanuseshukumar@...il.com>
> ---

All other calls to pci_epf_test_raise_irq() is done from the workqueue.

While we could change pci_epf_test_doorbell_handler() to queue some work on
the workqueue (and let that work call pci_epf_test_raise_irq()), converting
pci_epf_test_doorbell_handler() to be a threaded IRQ handler seems like the
less invasive change, thus:

Reviewed-by: Niklas Cassel <cassel@...nel.org>