On Thu, 2024-03-07 at 12:50 +0100, Nuno Sá wrote:
> Hi Herve,
>
>
> On Thu, 2024-03-07 at 12:10 +0100, Herve Codina wrote:
> > The commit 80dd33cf72d1 ("drivers: base: Fix device link removal")
> > introduces a workqueue to release the consumer and supplier devices used
> > in the devlink.
> > In the job queued, devices are release and in turn, when all the
> > references to these devices are dropped, the release function of the
> > device itself is called.
> >
> > Nothing is present to provide some synchronisation with this workqueue
> > in order to ensure that all ongoing releasing operations are done and
> > so, some other operations can be started safely.
> >
> > For instance, in the following sequence:
> > 1) of_platform_depopulate()
> > 2) of_overlay_remove()
> >
> > During the step 1, devices are released and related devlinks are removed
> > (jobs pushed in the workqueue).
> > During the step 2, OF nodes are destroyed but, without any
> > synchronisation with devlink removal jobs, of_overlay_remove() can raise
> > warnings related to missing of_node_put():
> > ERROR: memory leak, expected refcount 1 instead of 2
> >
> > Indeed, the missing of_node_put() call is going to be done, too late,
> > from the workqueue job execution.
> >
> > Introduce device_link_wait_removal() to offer a way to synchronize
> > operations waiting for the end of devlink removals (i.e. end of
> > workqueue jobs).
> > Also, as a flushing operation is done on the workqueue, the workqueue
> > used is moved from a system-wide workqueue to a local one.
> >
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Herve Codina <herve.codina@xxxxxxxxxxx>
> > Tested-by: Luca Ceresoli <luca.ceresoli@xxxxxxxxxxx>
> > Reviewed-by: Nuno Sa <nuno.sa@xxxxxxxxxx>
> > ---
> > drivers/base/core.c | 26 +++++++++++++++++++++++---
> > include/linux/device.h | 1 +
> > 2 files changed, 24 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > index d5f4e4aac09b..48b28c59c592 100644
> > --- a/drivers/base/core.c
> > +++ b/drivers/base/core.c
> > @@ -44,6 +44,7 @@ static bool fw_devlink_is_permissive(void);
> > static void __fw_devlink_link_to_consumers(struct device *dev);
> > static bool fw_devlink_drv_reg_done;
> > static bool fw_devlink_best_effort;
> > +static struct workqueue_struct *device_link_wq;
> >
> > /**
> > * __fwnode_link_add - Create a link between two fwnode_handles.
> > @@ -532,12 +533,26 @@ static void devlink_dev_release(struct device *dev)
> > /*
> > * It may take a while to complete this work because of the SRCU
> > * synchronization in device_link_release_fn() and if the consumer or
> > - * supplier devices get deleted when it runs, so put it into the "long"
> > - * workqueue.
> > + * supplier devices get deleted when it runs, so put it into the
> > + * dedicated workqueue.
> > */
> > - queue_work(system_long_wq, &link->rm_work);
> > + queue_work(device_link_wq, &link->rm_work);
> > }
> >
> > +/**
> > + * device_link_wait_removal - Wait for ongoing devlink removal jobs to terminate
> > + */
> > +void device_link_wait_removal(void)
> > +{
> > + /*
> > + * devlink removal jobs are queued in the dedicated work queue.
> > + * To be sure that all removal jobs are terminated, ensure that any
> > + * scheduled work has run to completion.
> > + */
> > + flush_workqueue(device_link_wq);
> > +}
> > +EXPORT_SYMBOL_GPL(device_link_wait_removal);
> > +
> > static struct class devlink_class = {
> > .name = "devlink",
> > .dev_groups = devlink_groups,
> > @@ -4099,9 +4114,14 @@ int __init devices_init(void)
> > sysfs_dev_char_kobj = kobject_create_and_add("char", dev_kobj);
> > if (!sysfs_dev_char_kobj)
> > goto char_kobj_err;
> > + device_link_wq = alloc_workqueue("device_link_wq", 0, 0);
>
> My rb tag was with the assumption this is moved into devlink_class_init(). IIUC,
> Saravana also agreed with that [1]. But it looks like he missed that we are
> allocating the queue in devices_init() and not in devlink_class_init().
>
> I'm also not sure if this is in line with what Rafael wanted for ccing stable. How
> do
> we know the next patch depends on this one?
Should have looked before:
https://www.kernel.org/doc/Documentation/process/stable-kernel-rules.rst
So, I think what you have is correct :)
- Nuno Sá
