Re: [PATCH v4 1/2] driver core: Introduce device_link_wait_removal()

[Luca Ceresoli]

On Wed,  6 Mar 2024 09:50:02 +0100
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.
> 
> Fixes: 80dd33cf72d1 ("drivers: base: Fix device link removal")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Herve Codina <herve.codina@xxxxxxxxxxx>

Tested-by: Luca Ceresoli <luca.ceresoli@xxxxxxxxxxx>

-- 
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com