Hi, On Thu, 22 Feb 2024 17:08:28 -0800 Saravana Kannan <saravanak@xxxxxxxxxx> wrote: > On Tue, Feb 20, 2024 at 10:56 PM Nuno Sá <noname.nuno@xxxxxxxxx> wrote: > > > > On Tue, 2024-02-20 at 16:31 -0800, Saravana Kannan wrote: > > > On Thu, Nov 30, 2023 at 9:41 AM Herve Codina <herve.codina@xxxxxxxxxxx> 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. > > > > > > Thanks for the bug report and fix. Sorry again about the delay in > > > reviewing the changes. > > > > > > Please add Fixes tag for 80dd33cf72d1. > > > > > > > Signed-off-by: Herve Codina <herve.codina@xxxxxxxxxxx> > > > > --- > > > > 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 ac026187ac6a..2e102a77758c 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 *fw_devlink_wq; > > > > > > > > /** > > > > * __fwnode_link_add - Create a link between two fwnode_handles. > > > > @@ -530,12 +531,26 @@ 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(fw_devlink_wq, &link->rm_work); > > > > > > This has nothing to do with fw_devlink. fw_devlink is just triggering > > > the issue in device links. You can hit this bug without fw_devlink too. > > > So call this device_link_wq since it's consistent with device_link_* APIs. > > > > > > > I'm not sure if I got this right in my series. I do call devlink_release_queue() to > > my queue. But on the Overlay side I use fwnode_links_flush_queue() because it looked > > more sensible from an OF point of view. And including (in OF code) linux/fwnode.h > > instead linux/device.h makes more sense to me. > > > > > > } > > > > > > > > +/** > > > > + * 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. > > > > + */ > > > > + drain_workqueue(fw_devlink_wq); > > > > > > Is there a reason this needs to be drain_workqueu() instead of > > > flush_workqueue(). Drain is a stronger guarantee than we need in this > > > case. All we are trying to make sure is that all the device link > > > remove work queued so far have completed. > > > > > > > Yeah, I'm also using flush_workqueue(). > > > > > > +} > > > > +EXPORT_SYMBOL_GPL(device_link_wait_removal); > > > > + > > > > static struct class devlink_class = { > > > > .name = "devlink", > > > > .dev_groups = devlink_groups, > > > > @@ -4085,9 +4100,14 @@ 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; > > > > + fw_devlink_wq = alloc_workqueue("fw_devlink_wq", 0, 0); > > > > + if (!fw_devlink_wq) > > > > > > Fix the name appropriately here too please. > > > > Hi Saravana, > > > > Oh, was not aware of this series... Please look at my first patch. It already has a > > review tag by Rafael. I think the creation of the queue makes more sense to be done > > in devlink_class_init(). Moreover, Rafael complained in my first version that > > erroring out because we failed to create the queue is too harsh since devlinks can > > still work. > > I think Rafael can be convinced on this one. Firstly, if we fail to > allocate so early, we have bigger problems. > > > So, what we do is to schedule the work if we have a queue or too call > > device_link_release_fn() synchronously if we don't have the queue (note that failing > > to allocate the queue is very unlikely anyways). > > device links don't really work when you synchronously need to delete a > link since it always uses SRCUs (it used to have a #ifndef CONFIG_SRCU > locking). That's like saying a code still works when it doesn't hit a > deadlock condition. > > Let's stick with Herve's patch series since he send it first and it > has fewer things that need to be fixed. If he ignores this thread for > too long, you can send a revision of yours again and we can accept > that. I don't ignore the thread :) Hope I could take some time in the near future to send a v2 of this series. Hervé