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Date: Tue, 15 Nov 2022 14:41:35 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Ira Weiny <ira.weiny@...el.com>
Cc: Dan Williams <dan.j.williams@...el.com>,
Bjorn Helgaas <bhelgaas@...gle.com>,
Gregory Price <gregory.price@...verge.com>,
Jonathan Cameron <Jonathan.Cameron@...wei.com>,
Alison Schofield <alison.schofield@...el.com>,
Vishal Verma <vishal.l.verma@...el.com>,
Ben Widawsky <bwidawsk@...nel.org>, linux-cxl@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH] PCI/doe: Fix work struct declaration
On Tue, Nov 15, 2022 at 12:18:38PM -0800, Ira Weiny wrote:
> On Tue, Nov 15, 2022 at 01:44:24PM -0600, Bjorn Helgaas wrote:
> > and say something more specific than "fix struct"?
>
> How about?
>
> PCI/DOE: Fix initialization of work struct in pci_doe_task
The importance of this has to do with whether something is on the
stack, so I think something about that would be useful.
I'm afraid this subject line bike-shedding has made you overlook my
other questions below ...
> > On Mon, Nov 14, 2022 at 05:19:43PM -0800, ira.weiny@...el.com wrote:
> > > From: Ira Weiny <ira.weiny@...el.com>
> > >
> > > The callers of pci_doe_submit_task() allocate the pci_doe_task on the
> > > stack. This causes the work structure to be allocated on the stack
> > > without pci_doe_submit_task() knowing. Work item initialization needs
> > > to be done with either INIT_WORK_ONSTACK() or INIT_WORK() depending on
> > > how the work item is allocated.
> > >
> > > Jonathan suggested creating doe task allocation macros such as
> > > DECLARE_CDAT_DOE_TASK_ONSTACK().[1] The issue with this is the work
> > > function is not known to the callers and must be initialized correctly.
> > >
> > > A follow up suggestion was to have an internal 'pci_doe_work' item
> > > allocated by pci_doe_submit_task().[2] This requires an allocation which
> > > could restrict the context where tasks are used.
> > >
> > > Compromise with an intermediate step to initialize the task struct with
> > > a new call pci_doe_init_task() which must be called prior to submit
> > > task.
> >
> > I'm not really a fan of passing a parameter to say "this struct is on
> > the stack" because that seems kind of error-prone and I don't know
> > what the consequence of getting it wrong would be. Sounds like it
> > *could* be some memory corruption or reading garbage data that would
> > be hard to debug.
> >
> > Do we have cases today where pci_doe_submit_task() can't do the
> > kzalloc() as in your patch at [3]? If the current use cases allow a
> > kzalloc(), why not do that now and defer this until it becomes an
> > issue?
> >
> > Bjorn
> >
> > > [1] https://lore.kernel.org/linux-cxl/20221014151045.24781-1-Jonathan.Cameron@huawei.com/T/#m88a7f50dcce52f30c8bf5c3dcc06fa9843b54a2d
> > > [2] https://lore.kernel.org/linux-cxl/20221014151045.24781-1-Jonathan.Cameron@huawei.com/T/#m63c636c5135f304480370924f4d03c00357be667
> >
> > [3] https://lore.kernel.org/linux-cxl/Y2AnKB88ALYm9c5L@iweiny-desk3/
> >
> > > Cc: Bjorn Helgaas <helgaas@...nel.org>
> > > Reported-by: Gregory Price <gregory.price@...verge.com>
> > > Reported-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> > > Suggested-by: Dan Williams <dan.j.williams@...el.com>
> > > Signed-off-by: Ira Weiny <ira.weiny@...el.com>
> > > ---
> > > drivers/cxl/core/pci.c | 2 ++
> > > drivers/pci/doe.c | 14 ++++++++++++--
> > > include/linux/pci-doe.h | 8 +++++---
> > > 3 files changed, 19 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c
> > > index 9240df53ed87..a19c1fa0e2f4 100644
> > > --- a/drivers/cxl/core/pci.c
> > > +++ b/drivers/cxl/core/pci.c
> > > @@ -525,6 +525,7 @@ static int cxl_cdat_get_length(struct device *dev,
> > > DECLARE_CDAT_DOE_TASK(CDAT_DOE_REQ(0), t);
> > > int rc;
> > >
> > > + pci_doe_init_task(cdat_doe, &t.task, true);
> > > rc = pci_doe_submit_task(cdat_doe, &t.task);
> > > if (rc < 0) {
> > > dev_err(dev, "DOE submit failed: %d", rc);
> > > @@ -554,6 +555,7 @@ static int cxl_cdat_read_table(struct device *dev,
> > > u32 *entry;
> > > int rc;
> > >
> > > + pci_doe_init_task(cdat_doe, &t.task, true);
> > > rc = pci_doe_submit_task(cdat_doe, &t.task);
> > > if (rc < 0) {
> > > dev_err(dev, "DOE submit failed: %d", rc);
> > > diff --git a/drivers/pci/doe.c b/drivers/pci/doe.c
> > > index e402f05068a5..cabeae4ae955 100644
> > > --- a/drivers/pci/doe.c
> > > +++ b/drivers/pci/doe.c
> > > @@ -319,6 +319,7 @@ static int pci_doe_discovery(struct pci_doe_mb *doe_mb, u8 *index, u16 *vid,
> > > };
> > > int rc;
> > >
> > > + pci_doe_init_task(doe_mb, &task, true);
> > > rc = pci_doe_submit_task(doe_mb, &task);
> > > if (rc < 0)
> > > return rc;
> > > @@ -495,6 +496,14 @@ bool pci_doe_supports_prot(struct pci_doe_mb *doe_mb, u16 vid, u8 type)
> > > }
> > > EXPORT_SYMBOL_GPL(pci_doe_supports_prot);
> > >
> > > +void pci_doe_init_task(struct pci_doe_mb *doe_mb, struct pci_doe_task *task,
> > > + bool onstack)
> > > +{
> > > + task->doe_mb = doe_mb;
> > > + __INIT_WORK(&task->work, doe_statemachine_work, onstack);
> > > +}
> > > +EXPORT_SYMBOL_GPL(pci_doe_init_task);
> > > +
> > > /**
> > > * pci_doe_submit_task() - Submit a task to be processed by the state machine
> > > *
> > > @@ -517,6 +526,9 @@ int pci_doe_submit_task(struct pci_doe_mb *doe_mb, struct pci_doe_task *task)
> > > if (!pci_doe_supports_prot(doe_mb, task->prot.vid, task->prot.type))
> > > return -EINVAL;
> > >
> > > + if (WARN_ON_ONCE(task->work.func != doe_statemachine_work))
> > > + return -EINVAL;
> > > +
> > > /*
> > > * DOE requests must be a whole number of DW and the response needs to
> > > * be big enough for at least 1 DW
> > > @@ -528,8 +540,6 @@ int pci_doe_submit_task(struct pci_doe_mb *doe_mb, struct pci_doe_task *task)
> > > if (test_bit(PCI_DOE_FLAG_DEAD, &doe_mb->flags))
> > > return -EIO;
> > >
> > > - task->doe_mb = doe_mb;
> > > - INIT_WORK(&task->work, doe_statemachine_work);
> > > queue_work(doe_mb->work_queue, &task->work);
> > > return 0;
> > > }
> > > diff --git a/include/linux/pci-doe.h b/include/linux/pci-doe.h
> > > index ed9b4df792b8..457fc0e53d64 100644
> > > --- a/include/linux/pci-doe.h
> > > +++ b/include/linux/pci-doe.h
> > > @@ -31,8 +31,8 @@ struct pci_doe_mb;
> > > * @rv: Return value. Length of received response or error (bytes)
> > > * @complete: Called when task is complete
> > > * @private: Private data for the consumer
> > > - * @work: Used internally by the mailbox
> > > - * @doe_mb: Used internally by the mailbox
> > > + * @work: Used internally by the mailbox [see pci_doe_init_task()]
> > > + * @doe_mb: Used internally by the mailbox [see pci_doe_init_task()]
> > > *
> > > * The payload sizes and rv are specified in bytes with the following
> > > * restrictions concerning the protocol.
> > > @@ -53,7 +53,7 @@ struct pci_doe_task {
> > > void (*complete)(struct pci_doe_task *task);
> > > void *private;
> > >
> > > - /* No need for the user to initialize these fields */
> > > + /* Call pci_doe_init_task() for these */
> > > struct work_struct work;
> > > struct pci_doe_mb *doe_mb;
> > > };
> > > @@ -72,6 +72,8 @@ struct pci_doe_task {
> > >
> > > struct pci_doe_mb *pcim_doe_create_mb(struct pci_dev *pdev, u16 cap_offset);
> > > bool pci_doe_supports_prot(struct pci_doe_mb *doe_mb, u16 vid, u8 type);
> > > +void pci_doe_init_task(struct pci_doe_mb *doe_mb, struct pci_doe_task *task,
> > > + bool onstack);
> > > int pci_doe_submit_task(struct pci_doe_mb *doe_mb, struct pci_doe_task *task);
> > >
> > > #endif
> > >
> > > base-commit: 30a0b95b1335e12efef89dd78518ed3e4a71a763
> > > --
> > > 2.37.2
> > >
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