Re: [PATCH] mm/zsmalloc: fix release order of locks in zs_page_migrate()

[Sergey Senozhatsky]

On (26/07/28 05:53), Richard Chang wrote:
> In zs_page_migrate(), locks are acquired in the following order:
>   1. write_lock(&pool->lock)
>   2. spin_lock(&class->lock)
>   3. zspage_write_trylock(zspage)
> 
> However, upon successful page migration, they were being released in
> forward acquisition (FIFO) order:
>   1. write_unlock(&pool->lock)
>   2. spin_unlock(&class->lock)
>   3. zspage_write_unlock(zspage)
> 
> Fix the unlocking order to release locks in strict reverse (LIFO)
> order of acquisition:
>   3. zspage_write_unlock(zspage)
>   2. spin_unlock(&class->lock)
>   1. write_unlock(&pool->lock)
> 
> Releasing locks in reverse order of acquisition adheres to standard
> kernel locking hygiene, prevents potential lock ordering and lockdep
> inconsistencies.
> 
> Signed-off-by: Richard Chang <richardycc@xxxxxxxxxx>

Reviewed-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>
Tested-by: Sergey Senozhatsky <senozhatsky@xxxxxxxxxxxx>