* [PATCH v2] driver core: Fix device_pm_lock() locking for device links
@ 2020-09-01 18:44 Saravana Kannan
2020-09-02 1:11 ` Peng Fan
0 siblings, 1 reply; 2+ messages in thread
From: Saravana Kannan @ 2020-09-01 18:44 UTC (permalink / raw)
To: Greg Kroah-Hartman, Rafael J. Wysocki, Saravana Kannan
Cc: linux-imx, linux-arm-kernel, Dong Aisheng, Shawn Guo,
Sascha Hauer, linux, m.szyprowski, naresh.kamboju, Peng Fan,
Stephen Boyd, Dong Aisheng, kernel-team, linux-kernel
This commit fixes two issues:
1. The lockdep warning reported by Dong Aisheng <dongas86@gmail.com> [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 <dongas86@gmail.com>
Signed-off-by: Saravana Kannan <saravanak@google.com>
---
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
^ permalink raw reply related [flat|nested] 2+ messages in thread
* RE: [PATCH v2] driver core: Fix device_pm_lock() locking for device links
2020-09-01 18:44 [PATCH v2] driver core: Fix device_pm_lock() locking for device links Saravana Kannan
@ 2020-09-02 1:11 ` Peng Fan
0 siblings, 0 replies; 2+ messages in thread
From: Peng Fan @ 2020-09-02 1:11 UTC (permalink / raw)
To: Saravana Kannan, Greg Kroah-Hartman, Rafael J. Wysocki
Cc: dl-linux-imx, linux-arm-kernel, Aisheng Dong, Shawn Guo,
Sascha Hauer, linux, m.szyprowski, naresh.kamboju, Stephen Boyd,
Dong Aisheng, kernel-team, linux-kernel
> 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 <dongas86@gmail.com>
> [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 <dongas86@gmail.com>
> Signed-off-by: Saravana Kannan <saravanak@google.com>
Tested-by: Peng Fan <peng.fan@nxp.com>
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
^ permalink raw reply [flat|nested] 2+ messages in thread
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