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Message-ID: <c0f7ea40a2b1abc22242a892e162e4511a7c99f1.camel@gmail.com>
Date: Thu, 07 Mar 2024 13:29:19 +0100
From: Nuno Sá <noname.nuno@...il.com>
To: Herve Codina <herve.codina@...tlin.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "Rafael J. Wysocki"
<rafael@...nel.org>, Rob Herring <robh+dt@...nel.org>, Frank Rowand
<frowand.list@...il.com>, Saravana Kannan <saravanak@...gle.com>, Lizhi Hou
<lizhi.hou@....com>, Max Zhen <max.zhen@....com>, Sonal Santan
<sonal.santan@....com>, Stefano Stabellini <stefano.stabellini@...inx.com>,
Jonathan Cameron <Jonathan.Cameron@...wei.com>,
linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, Allan Nielsen
<allan.nielsen@...rochip.com>, Horatiu Vultur
<horatiu.vultur@...rochip.com>, Steen Hegelund
<steen.hegelund@...rochip.com>, Luca Ceresoli <luca.ceresoli@...tlin.com>,
Nuno Sa <nuno.sa@...log.com>, Thomas Petazzoni
<thomas.petazzoni@...tlin.com>, stable@...r.kernel.org
Subject: Re: [PATCH v5 1/2] driver core: Introduce device_link_wait_removal()
On Thu, 2024-03-07 at 13:16 +0100, Herve Codina wrote:
> Hi Nuno,
>
> On Thu, 07 Mar 2024 12:50:52 +0100
> Nuno Sá <noname.nuno@...il.com> 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@...r.kernel.org
> > > Signed-off-by: Herve Codina <herve.codina@...tlin.com>
> > > Tested-by: Luca Ceresoli <luca.ceresoli@...tlin.com>
> > > Reviewed-by: Nuno Sa <nuno.sa@...log.com>
> > > ---
> > > 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?
> >
> > [1]:
> > https://lore.kernel.org/lkml/CAGETcx_gNWOTsSZMaZu+XU1-5Z60WEcMhw08t4Sn_-YgkCCUmA@mail.gmail.com/
> >
>
> We discussed that point and I understood that you were ok to do that on your
> side:
>
> https://lore.kernel.org/linux-kernel/f42ceee61ddb8b50c347589649d4131476ab5d81.camel@gmail.com/
>
> Sorry if I misunderstood.
Oh, yeah, I can do that. But given Saravana reply I thought the expectation is to
have the queue already allocated in devlink_class_init().
>
> I am going to wait for other comments on this current series before re-sending
> with our 'Reviewed-by' removed if needed. Let me know.
>
Anyways, if your expectation was for me to do it later, fine. No need to remove the
tag. Sorry for the noise.
- Nuno Sá
>
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