Re: [PATCH v2 01/10] PCI/DOE: Silence WARN splat with CONFIG_DEBUG_OBJECTS=y

From: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
To: Ira Weiny <ira.weiny@intel.com>
Cc: Lukas Wunner <lukas@wunner.de>,
	Bjorn Helgaas <helgaas@kernel.org>, <linux-pci@vger.kernel.org>,
	Gregory Price <gregory.price@memverge.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Alison Schofield <alison.schofield@intel.com>,
	Vishal Verma <vishal.l.verma@intel.com>,
	Dave Jiang <dave.jiang@intel.com>,
	"Li, Ming" <ming4.li@intel.com>,
	"Hillf Danton" <hdanton@sina.com>,
	Ben Widawsky <bwidawsk@kernel.org>, <linuxarm@huawei.com>,
	<linux-cxl@vger.kernel.org>
Subject: Re: [PATCH v2 01/10] PCI/DOE: Silence WARN splat with CONFIG_DEBUG_OBJECTS=y
Date: Tue, 24 Jan 2023 10:32:08 +0000	[thread overview]
Message-ID: <20230124103208.00000675@Huawei.com> (raw)
In-Reply-To: <63cf276083fe1_4a9a29468@iweiny-mobl.notmuch>

On Mon, 23 Jan 2023 16:33:36 -0800
Ira Weiny <ira.weiny@intel.com> wrote:

> Lukas Wunner wrote:
> > Gregory Price reports a WARN splat with CONFIG_DEBUG_OBJECTS=y upon CXL
> > probing because pci_doe_submit_task() invokes INIT_WORK() instead of
> > INIT_WORK_ONSTACK() for a work_struct that was allocated on the stack.
> > 
> > All callers of pci_doe_submit_task() allocate the work_struct on the
> > stack, so replace INIT_WORK() with INIT_WORK_ONSTACK() as a backportable
> > short-term fix.
> > 
> > Stacktrace for posterity:
> > 
> > WARNING: CPU: 0 PID: 23 at lib/debugobjects.c:545 __debug_object_init.cold+0x18/0x183
> > CPU: 0 PID: 23 Comm: kworker/u2:1 Not tainted 6.1.0-0.rc1.20221019gitaae703b02f92.17.fc38.x86_64 #1
> > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
> > Call Trace:
> >  pci_doe_submit_task+0x5d/0xd0
> >  pci_doe_discovery+0xb4/0x100
> >  pcim_doe_create_mb+0x219/0x290
> >  cxl_pci_probe+0x192/0x430
> >  local_pci_probe+0x41/0x80
> >  pci_device_probe+0xb3/0x220
> >  really_probe+0xde/0x380
> >  __driver_probe_device+0x78/0x170
> >  driver_probe_device+0x1f/0x90
> >  __driver_attach_async_helper+0x5c/0xe0
> >  async_run_entry_fn+0x30/0x130
> >  process_one_work+0x294/0x5b0
> > 
> > Fixes: 9d24322e887b ("PCI/DOE: Add DOE mailbox support functions")
> > Link: https://lore.kernel.org/linux-cxl/Y1bOniJliOFszvIK@memverge.com/
> > Reported-by: Gregory Price <gregory.price@memverge.com>
> > Tested-by: Ira Weiny <ira.weiny@intel.com>  
> 
> Reviewed-by: Ira Weiny <ira.weiny@intel.com>

It's an unusual requirement, but this is indeed the minimal fix
given current users.  Obviously becomes more sensible later in the
series once you make the API synchronous only.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huwei.com>

> 
> > Signed-off-by: Lukas Wunner <lukas@wunner.de>
> > Cc: stable@vger.kernel.org # v6.0+
> > Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > ---
> >  Changes v1 -> v2:
> >   * Add note in kernel-doc of pci_doe_submit_task() that pci_doe_task must
> >     be allocated on the stack (Jonathan)
> > 
> >  drivers/pci/doe.c | 4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/pci/doe.c b/drivers/pci/doe.c
> > index 66d9ab288646..12a6752351bf 100644
> > --- a/drivers/pci/doe.c
> > +++ b/drivers/pci/doe.c
> > @@ -520,6 +520,8 @@ EXPORT_SYMBOL_GPL(pci_doe_supports_prot);
> >   * task->complete will be called when the state machine is done processing this
> >   * task.
> >   *
> > + * @task must be allocated on the stack.
> > + *
> >   * Excess data will be discarded.
> >   *
> >   * RETURNS: 0 when task has been successfully queued, -ERRNO on error
> > @@ -541,7 +543,7 @@ int pci_doe_submit_task(struct pci_doe_mb *doe_mb, struct pci_doe_task *task)
> >  		return -EIO;
> >  
> >  	task->doe_mb = doe_mb;
> > -	INIT_WORK(&task->work, doe_statemachine_work);
> > +	INIT_WORK_ONSTACK(&task->work, doe_statemachine_work);
> >  	queue_work(doe_mb->work_queue, &task->work);
> >  	return 0;
> >  }
> > -- 
> > 2.39.1
> >   
> 
> 