linux-kernel - Re: [PATCH V2] drivers: core: Remove glue dirs early only when refcount is 1

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Date:   Wed, 1 May 2019 08:53:13 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Prateek Sood <prsood@...eaurora.org>
Cc:     rafael@...nel.org, sramana@...eaurora.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] drivers: core: Remove glue dirs early only when
 refcount is 1

On Wed, May 01, 2019 at 09:52:47AM +0530, Prateek Sood wrote:
> While loading firmware blobs parallely in different threads, it is possible
> to free sysfs node of glue_dirs in device_del() from a thread while another
> thread is trying to add subdir from device_add() in glue_dirs sysfs node.
> 
>     CPU1                                           CPU2
> fw_load_sysfs_fallback()
>   device_add()
>     get_device_parent()
>       class_dir_create_and_add()
>         kobject_add_internal()
>           create_dir() // glue_dir
> 
>                                            fw_load_sysfs_fallback()
>                                              device_add()
>                                                get_device_parent()
>                                                  kobject_get() //glue_dir
> 
>   device_del()
>     cleanup_glue_dir()
>       kobject_del()
> 
>                                                kobject_add()
>                                                  kobject_add_internal()
>                                                    create_dir() // in glue_dir
>                                                      kernfs_create_dir_ns()
> 
>        sysfs_remove_dir() //glue_dir->sd=NULL
>        sysfs_put() // free glue_dir->sd
> 
>                                                        kernfs_new_node()
>                                                          kernfs_get(glue_dir)
> 
> Fix this race by making sure that kernfs_node for glue_dir is released only
> when refcount for glue_dir kobj is 1.
> 
> Signed-off-by: Prateek Sood <prsood@...eaurora.org>
> ---
>  drivers/base/core.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)

What changed from v1?  That always has to go below the --- line.

v3 please.