[PATCH for-4.19 06/12] staging: erofs: fix race when the managed cache is enabled

[Greg Kroah-Hartman]

On Wed, Feb 20, 2019 at 05:18:48PM +0800, Gao Xiang wrote:
> commit 51232df5e4b268936beccde5248f312a316800be upstream.
> 
> When the managed cache is enabled, the last reference count
> of a workgroup must be used for its workstation.
> 
> Otherwise, it could lead to incorrect (un)freezes in
> the reclaim path, and it would be harmful.
> 
> A typical race as follows:
> 
> Thread 1 (In the reclaim path)  Thread 2
> workgroup_freeze(grp, 1)                                refcnt = 1
> ...
> workgroup_unfreeze(grp, 1)                              refcnt = 1
>                                 workgroup_get(grp)      refcnt = 2 (x)
> workgroup_put(grp)                                      refcnt = 1 (x)
>                                 ...unexpected behaviors
> 
> * grp is detached but still used, which violates cache-managed
>   freeze constraint.
> 
> Reviewed-by: Chao Yu <yuchao0 at huawei.com>
> Signed-off-by: Gao Xiang <gaoxiang25 at huawei.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> Signed-off-by: Gao Xiang <gaoxiang25 at huawei.com>
> 
> Conflicts:
> 	drivers/staging/erofs/utils.c
> Updates:
> 	include/linux/xarray.h:
> 		add xa_untag_pointer,xa_tag_pointer,xa_pointer_tag
> 		from upstream 3159f943aafd in order to reduce
> 		conflicts.

No, sorry, I don't want to add xarray.h to 4.19.y, that's crazy.

And even if we did, you do not slip it in as part of a different patch,
it should come in as its own patch, with the same git commit id that it
landed in 4.20 with.

Please fix this up...

greg k-h