Re: [PATCH v1] driver core: Fix scheduling while atomic warnings during device link deletion

[Guenter Roeck <linux@roeck-us.net>]

On 7/15/20 10:08 PM, Saravana Kannan wrote:
> Marek and Guenter reported that commit 287905e68dd2 ("driver core:
> Expose device link details in sysfs") caused sleeping/scheduling while
> atomic warnings.
> 
> BUG: sleeping function called from invalid context at kernel/locking/mutex.c:935
> in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 12, name: kworker/0:1
> 2 locks held by kworker/0:1/12:
>   #0: ee8074a8 ((wq_completion)rcu_gp){+.+.}-{0:0}, at: process_one_work+0x174/0x7dc
>   #1: ee921f20 ((work_completion)(&sdp->work)){+.+.}-{0:0}, at: process_one_work+0x174/0x7dc
> Preemption disabled at:
> [<c01b10f0>] srcu_invoke_callbacks+0xc0/0x154
> ----- 8< ----- SNIP
> [<c064590c>] (device_del) from [<c0645c9c>] (device_unregister+0x24/0x64)
> [<c0645c9c>] (device_unregister) from [<c01b10fc>] (srcu_invoke_callbacks+0xcc/0x154)
> [<c01b10fc>] (srcu_invoke_callbacks) from [<c01493c4>] (process_one_work+0x234/0x7dc)
> [<c01493c4>] (process_one_work) from [<c01499b0>] (worker_thread+0x44/0x51c)
> [<c01499b0>] (worker_thread) from [<c0150bf4>] (kthread+0x158/0x1a0)
> [<c0150bf4>] (kthread) from [<c0100114>] (ret_from_fork+0x14/0x20)
> Exception stack(0xee921fb0 to 0xee921ff8)
> 
> This was caused by the device link device being released in the context
> of srcu_invoke_callbacks().  There is no need to wait till the RCU
> callback to release the device link device.  So release the device
> earlier and revert the RCU callback code to what it was before
> commit 287905e68dd2 ("driver core: Expose device link details in sysfs")
> 
> Fixes: 287905e68dd2 ("driver core: Expose device link details in sysfs")
> Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
> Reported-by: Guenter Roeck <linux@roeck-us.net>
> Signed-off-by: Saravana Kannan <saravanak@google.com>
> ---
> Marek and Guenter,
> 
> It haven't had a chance to test this yet. Can one of you please test it
> and confirm it fixes the issue?
> 

With this patch applied, the original warning is gone, but I get lots
of other warnings.

WARNING: CPU: 0 PID: 1 at drivers/base/core.c:1790 device_release+0x94/0xa4^M
Device 'regulators:regulator@0:50038000.ethernet' does not have a release() function, it is broken and must be fixed.

WARNING: CPU: 0 PID: 1 at drivers/base/core.c:1790 device_release+0x94/0xa4
Device '53f9c000.gpio:50038000.ethernet' does not have a release() function, it is broken and must be fixed.

WARNING: CPU: 0 PID: 1 at drivers/base/core.c:1790 device_release+0x94/0xa4^M
Device '50030000.tscadc:50030400.tcq' does not have a release() function, it is broken and must be fixed.

and so on. I don't know if this is caused by this patch or by
some other patch in -next.

Guenter

> Thanks,
> Saravana
> 
>  drivers/base/core.c | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 5373ddd029f6..ccb2ce11f5b5 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -306,16 +306,10 @@ static struct attribute *devlink_attrs[] = {
>  };
>  ATTRIBUTE_GROUPS(devlink);
>  
> -static void devlink_dev_release(struct device *dev)
> -{
> -	kfree(to_devlink(dev));
> -}
> -
>  static struct class devlink_class = {
>  	.name = "devlink",
>  	.owner = THIS_MODULE,
>  	.dev_groups = devlink_groups,
> -	.dev_release = devlink_dev_release,
>  };
>  
>  static int devlink_add_symlinks(struct device *dev,
> @@ -737,7 +731,7 @@ static void device_link_free(struct device_link *link)
>  
>  	put_device(link->consumer);
>  	put_device(link->supplier);
> -	device_unregister(&link->link_dev);
> +	kfree(link);
>  }
>  
>  #ifdef CONFIG_SRCU
> @@ -756,6 +750,7 @@ static void __device_link_del(struct kref *kref)
>  	if (link->flags & DL_FLAG_PM_RUNTIME)
>  		pm_runtime_drop_link(link->consumer);
>  
> +	device_unregister(&link->link_dev);
>  	list_del_rcu(&link->s_node);
>  	list_del_rcu(&link->c_node);
>  	call_srcu(&device_links_srcu, &link->rcu_head, __device_link_free_srcu);
> @@ -771,6 +766,7 @@ static void __device_link_del(struct kref *kref)
>  	if (link->flags & DL_FLAG_PM_RUNTIME)
>  		pm_runtime_drop_link(link->consumer);
>  
> +	device_unregister(&link->link_dev);
>  	list_del(&link->s_node);
>  	list_del(&link->c_node);
>  	device_link_free(link);
>