On Thu, Mar 26, 2020 at 12:02:33AM -0700, Michel Lespinasse wrote: > @@ -47,9 +48,9 @@ static inline void activate_mm(struct mm_struct *old, struct mm_struct *new) > * when the new ->mm is used for the first time. > */ > __switch_mm(&new->context.id); > - down_write_nested(&new->mmap_sem, 1); > + mmap_write_lock_nested(new, 1); > uml_setup_stubs(new); > - mmap_write_unlock(new); > + mmap_write_unlock_nested(new); This is a bit of an oddity. We don't usually have an unlock_nested() variant (a quick grep finds only something complicated in reiserfs). That's because it's legitimate to release locks in a different order from the one they were acquired in (eg lock A, lock B, unlock A, unlock B), and it's not clear whether "nested" would follow the lock (ie unlock_nested B) or whether it would follow the code (ie unlock_nested A). Does your future API require knowing the nested nature at the unlock point? And if so, does it require it for A or B in the above scenario? And how does it mix with lock A or B being of a different type (eg a plain mutex or a spinlock)?
