Re: [PATCH] drm/bridge: megachips: Fix error handling in i2c_register_driver()

[Andrzej Hajda]

On 08.11.2022 09:29, Yuan Can wrote:

A problem about insmod megachips-stdpxxxx-ge-b850v3-fw.ko failed is
triggered with the following log given:

[ 4497.981497] Error: Driver 'stdp4028-ge-b850v3-fw' is already registered, 
aborting...
insmod: ERROR: could not insert module megachips-stdpxxxx-ge-b850v3-fw.ko: 
Device or resource busy

The reason is that stdpxxxx_ge_b850v3_init() returns i2c_add_driver()
directly without checking its return value, if i2c_add_driver() failed,
it returns without calling i2c_del_driver() on the previous i2c driver,
resulting the megachips-stdpxxxx-ge-b850v3-fw can never be installed
later.
A simple call graph is shown as below:

  stdpxxxx_ge_b850v3_init()
    i2c_add_driver(&stdp4028_ge_b850v3_fw_driver)
    i2c_add_driver(&stdp2690_ge_b850v3_fw_driver)
      i2c_register_driver()
        driver_register()
          bus_add_driver()
            priv = kzalloc(...) # OOM happened
    # return without delete stdp4028_ge_b850v3_fw_driver

Fix by calling i2c_del_driver() on stdp4028_ge_b850v3_fw_driver when
i2c_add_driver() returns error.

Fixes: fcfa0ddc18ed ("drm/bridge: Drivers for megachips-stdpxxxx-ge-b850v3-fw 
(LVDS-DP++)")
Signed-off-by: Yuan Can <yuan...@huawei.com>
---
  drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c | 8 +++++++-
  1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c 
b/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
index 97359f807bfc..0d037eeefcf3 100644
--- a/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
+++ b/drivers/gpu/drm/bridge/megachips-stdpxxxx-ge-b850v3-fw.c
@@ -440,7 +440,13 @@ static int __init stdpxxxx_ge_b850v3_init(void)
        if (ret)
                return ret;

- return i2c_add_driver(&stdp2690_ge_b850v3_fw_driver);

+       ret = i2c_add_driver(&stdp2690_ge_b850v3_fw_driver);
+       if (ret) {
+               i2c_del_driver(&stdp4028_ge_b850v3_fw_driver);
+               return ret;
+       }
+
+       return 0;

Could be:
ret = i2c_add_driver(&stdp2690_ge_b850v3_fw_driver);
if (ret)
    i2c_del_driver(&stdp4028_ge_b850v3_fw_driver);
return ret;

Up to you. Anyway:
Reviewed-by: Andrzej Hajda <andrzej.ha...@intel.com>

Regards
Andrzej

  }
  module_init(stdpxxxx_ge_b850v3_init);