> Subject: [PATCH v2] driver core: Fix device_pm_lock() locking for device links
>
> This commit fixes two issues:
>
> 1. The lockdep warning reported by Dong Aisheng <[email protected]>
> [1].
>
> It is a warning about a cycle (dpm_list_mtx --> kn->active#3 --> fw_lock) that
> was introduced when device-link devices were added to expose device link
> information in sysfs.
>
> The patch that "introduced" this cycle can't be reverted because it's fixes a
> real SRCU issue and also ensures that the device-link device is deleted as
> soon as the device-link is deleted. This is important to avoid sysfs name
> collisions if the device-link is create again immediately (this can happen a lot
> with deferred probing).
>
> 2. Inconsistency in grabbing device_pm_lock() during device link deletion
>
> Some device link deletion code paths grab device_pm_lock(), while others
> don't. The device_pm_lock() is grabbed during device_link_add() because it
> checks if the supplier is in the dpm_list and also reorders the dpm_list.
> However, when a device link is deleted, it does not do either of those and
> therefore device_pm_lock() is not necessary. Dropping the device_pm_lock()
> in all the device link deletion paths removes the inconsistency in locking.
>
> Thanks to Stephen Boyd for helping me understand the lockdep splat.
>
> Fixes: 843e600b8a2b ("driver core: Fix sleeping in invalid context during
> device link deletion") [1] -
> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.ke
> rnel.org%2Flkml%2FCAA%2BhA%3DS4eAreb7vo69LAXSk2t5%3DDEKNxHaiY1
> wSpk4xTp9urLg%40mail.gmail.com%2F&data=02%7C01%7Cpeng.fan%4
> 0nxp.com%7Cc07e23dccfa84d96b17808d84ea71bb9%7C686ea1d3bc2b4c6f
> a92cd99c5c301635%7C0%7C0%7C637345826922594698&sdata=X0Pzb
> ni5QcjxOCWkfR9uvxRcfvpzPQSNMmk%2BJf93dYI%3D&reserved=0
> Reported-by: Dong Aisheng <[email protected]>
> Signed-off-by: Saravana Kannan <[email protected]>
Tested-by: Peng Fan <[email protected]>
Thanks,
Peng.
> ---
>
> Cc'ing everyone from the original thread [1]
>
> -Saravana
>
> drivers/base/core.c | 4 ----
> 1 file changed, 4 deletions(-)
>
> diff --git a/drivers/base/core.c b/drivers/base/core.c index
> f6f620aa9408..07e5ceb40bb1 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -807,9 +807,7 @@ static void device_link_put_kref(struct device_link
> *link) void device_link_del(struct device_link *link) {
> device_links_write_lock();
> - device_pm_lock();
> device_link_put_kref(link);
> - device_pm_unlock();
> device_links_write_unlock();
> }
> EXPORT_SYMBOL_GPL(device_link_del);
> @@ -830,7 +828,6 @@ void device_link_remove(void *consumer, struct
> device *supplier)
> return;
>
> device_links_write_lock();
> - device_pm_lock();
>
> list_for_each_entry(link, &supplier->links.consumers, s_node) {
> if (link->consumer == consumer) {
> @@ -839,7 +836,6 @@ void device_link_remove(void *consumer, struct
> device *supplier)
> }
> }
>
> - device_pm_unlock();
> device_links_write_unlock();
> }
> EXPORT_SYMBOL_GPL(device_link_remove);
> --
> 2.28.0.402.g5ffc5be6b7-goog