Re: Should shadow_lock be spin_lock_recursive?

[Xiaofeng Ling <xiaofeng.ling@intel.com>]

This dead lock happened on VNIF code when enabled shadow mode.
The shadow_lock path is so complex and maybe using recurisve lock
is the easiest way to avoid dead lock currently before clearing
the path or splitting the lock .

Arun Sharma wrote:
> 
> During our testing, we found this code path where xen attempts to grab 
> the shadow_lock, while holding it - leading to a deadlock.
> 
>  >> free_dom_mem->
>  >> shadow_sync_and_drop_references->
>  >> shadow_lock -> ..................... first lock
>  >> shadow_remove_all_access->
>  >> remove_all_access_in_page->
>  >> put_page->
>  >> free_domheap_pages->
>  >> shadow_drop_references->
>  >> shadow_lock -> ..................... second lock
> 
> Questions:
> 
> - should shadow lock be recursive?
> - is shadow lock too coarse grained? It seems to have led to a lot of 
> code refactoring (__foo without lock and foo with lock). But there may 
> be more such instances we haven't found yet.
> 
>     -Arun