Re: [RFC PATCH] software node: balance refcount for managed sw nodes

From: Heikki Krogerus <heikki.krogerus@linux.intel.com>
To: laurentiu.tudor@nxp.com
Cc: andriy.shevchenko@linux.intel.com, gregkh@linuxfoundation.org,
	rafael@kernel.org, linux-acpi@vger.kernel.org,
	linux-kernel@vger.kernel.org, jon@solid-run.com
Subject: Re: [RFC PATCH] software node: balance refcount for managed sw nodes
Date: Fri, 16 Jul 2021 12:32:14 +0300	[thread overview]
Message-ID: <YPFSHiHZzjwJD2PI@kuha.fi.intel.com> (raw)
In-Reply-To: <20210716081711.7638-1-laurentiu.tudor@nxp.com>

Fri, Jul 16, 2021 at 11:17:11AM +0300, laurentiu.tudor@nxp.com kirjoitti:
> From: Laurentiu Tudor <laurentiu.tudor@nxp.com>
> 
> software_node_notify(), on KOBJ_REMOVE drops the refcount twice on managed
> software nodes, thus leading to underflow errors. Balance the refcount by
> bumping it in the device_create_managed_software_node() function.
> 
> The error [1] was encountered after adding a .shutdown() op to our
> fsl-mc-bus driver.
> 
> [1]
> pc : refcount_warn_saturate+0xf8/0x150
> lr : refcount_warn_saturate+0xf8/0x150
> sp : ffff80001009b920
> x29: ffff80001009b920 x28: ffff1a2420318000 x27: 0000000000000000
> x26: ffffccac15e7a038 x25: 0000000000000008 x24: ffffccac168e0030
> x23: ffff1a2428a82000 x22: 0000000000080000 x21: ffff1a24287b5000
> x20: 0000000000000001 x19: ffff1a24261f4400 x18: ffffffffffffffff
> x17: 6f72645f726f7272 x16: 0000000000000000 x15: ffff80009009b607
> x14: 0000000000000000 x13: ffffccac16602670 x12: 0000000000000a17
> x11: 000000000000035d x10: ffffccac16602670 x9 : ffffccac16602670
> x8 : 00000000ffffefff x7 : ffffccac1665a670 x6 : ffffccac1665a670
> x5 : 0000000000000000 x4 : 0000000000000000 x3 : 00000000ffffffff
> x2 : 0000000000000000 x1 : 0000000000000000 x0 : ffff1a2420318000
> Call trace:
>  refcount_warn_saturate+0xf8/0x150
>  kobject_put+0x10c/0x120
>  software_node_notify+0xd8/0x140
>  device_platform_notify+0x4c/0xb4
>  device_del+0x188/0x424
>  fsl_mc_device_remove+0x2c/0x4c
>  rebofind sp.c__fsl_mc_device_remove+0x14/0x2c
>  device_for_each_child+0x5c/0xac
>  dprc_remove+0x9c/0xc0
>  fsl_mc_driver_remove+0x28/0x64
>  __device_release_driver+0x188/0x22c
>  device_release_driver+0x30/0x50
>  bus_remove_device+0x128/0x134
>  device_del+0x16c/0x424
>  fsl_mc_bus_remove+0x8c/0x114
>  fsl_mc_bus_shutdown+0x14/0x20
>  platform_shutdown+0x28/0x40
>  device_shutdown+0x15c/0x330
>  __do_sys_reboot+0x218/0x2a0
>  __arm64_sys_reboot+0x28/0x34
>  invoke_syscall+0x48/0x114
>  el0_svc_common+0x40/0xdc
>  do_el0_svc+0x2c/0x94
>  el0_svc+0x2c/0x54
>  el0t_64_sync_handler+0xa8/0x12c
>  el0t_64_sync+0x198/0x19c
> ---[ end trace 32eb1c71c7d86821 ]---
> 
> Reported-by: Jon Nettleton <jon@solid-run.com>
> Signed-off-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
> ---
>  drivers/base/swnode.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/base/swnode.c b/drivers/base/swnode.c
> index d1f1a8240120..907616ca487f 100644
> --- a/drivers/base/swnode.c
> +++ b/drivers/base/swnode.c
> @@ -1113,6 +1113,8 @@ int device_create_managed_software_node(struct device *dev,
>  	to_swnode(fwnode)->managed = true;
>  	set_secondary_fwnode(dev, fwnode);
>  
> +	kobject_get(&to_swnode(fwnode)->kobj);
> +
>  	return 0;
>  }
>  EXPORT_SYMBOL_GPL(device_create_managed_software_node);

We can't increment the refcount uncoditionally like that. Would this
work instead:

diff --git a/drivers/base/swnode.c b/drivers/base/swnode.c
index d1f1a82401207..bdb50a06c82ae 100644
--- a/drivers/base/swnode.c
+++ b/drivers/base/swnode.c
@@ -1113,6 +1113,9 @@ int device_create_managed_software_node(struct device *dev,
        to_swnode(fwnode)->managed = true;
        set_secondary_fwnode(dev, fwnode);
 
+       if (device_is_registered(dev))
+               software_node_notify(dev, KOBJ_ADD);
+
        return 0;
 }
 EXPORT_SYMBOL_GPL(device_create_managed_software_node);

thanks,

-- 
heikki
