From 6b57b15abe11aa334ebf726e02c0deaf123ba040 Mon Sep 17 00:00:00 2001 From: Saravana Kannan Date: Tue, 1 Sep 2020 11:44:44 -0700 Subject: [PATCH] driver core: Fix device_pm_lock() locking for device links This commit fixes two issues: 1. The lockdep warning reported by Dong Aisheng [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://lore.kernel.org/lkml/CAA+hA=S4eAreb7vo69LAXSk2t5=DEKNxHaiY1wSpk4xTp9urLg@mail.gmail.com/ Reported-by: Dong Aisheng Signed-off-by: Saravana Kannan Tested-by: Peng Fan Link: https://lore.kernel.org/r/20200901184445.1736658-1-saravanak@google.com Signed-off-by: Greg Kroah-Hartman --- drivers/base/core.c | 4 ---- 1 file changed, 4 deletions(-) diff --git a/drivers/base/core.c b/drivers/base/core.c index 1a4706310b28..97812a5f42b8 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);