Re: [PATCH] sysfs_remove_dir Vs dcache_readdir race fix

[Andrew Morton]

Maneesh Soni <maneesh@xxxxxxxxxx> wrote:
>
> Actually race is not directly between dcache_readdir and sysfs_remove_dir but
>  it is like this
> 
>  cpu 0						cpu 1
>  dcache_dir_open()
>  --> adds the cursor dentry
> 
>  					sysfs_remove_dir()
>  					--> list_del_init cursor dentry
> 
>  dcache_readdir()
>  --> loops forever on inititalized cursor dentry.
> 
> 
>  Though all these operations happen under parent's i_sem, but it is dropped 
>  between ->open() and ->readdir() as both are different calls. 
> 
>  I think people will also agree that there is no need for sysfs_remove_dir() 
>  to modify d_subdirs list.

Seems to me that the libfs code is fragile.

What happens if the dentry at filp->f_private_data gets moved to a
different directory after someone did dcache_dir_open()?  Does the loop
in dcache_readdir() go infinite again?

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