Re: [PATCH v5.5 10/10] mmap locking API: rename mmap_sem to mmap_lock

[Laurent Dufour <ldufour@linux.ibm.com>]

Le 24/04/2020 à 03:39, Michel Lespinasse a écrit :
> Rename the mmap_sem field to mmap_lock. Any new uses of this lock
> should now go through the new mmap locking api. The mmap_lock is
> still implemented as a rwsem, though this could change in the future.
> 
> Signed-off-by: Michel Lespinasse <walken@google.com>
> ---
>   arch/ia64/mm/fault.c                  |  4 +--
>   arch/x86/mm/fault.c                   |  2 +-
>   drivers/gpu/drm/etnaviv/etnaviv_gem.c |  2 +-
>   include/linux/mm_types.h              |  2 +-
>   include/linux/mmap_lock.h             | 38 +++++++++++++--------------
>   mm/memory.c                           |  2 +-
>   mm/mmap.c                             |  4 +--
>   mm/mmu_notifier.c                     |  2 +-
>   8 files changed, 28 insertions(+), 28 deletions(-)
> 
> diff --git a/arch/ia64/mm/fault.c b/arch/ia64/mm/fault.c
> index 693f00b117e1..9b95050c2048 100644
> --- a/arch/ia64/mm/fault.c
> +++ b/arch/ia64/mm/fault.c
> @@ -70,8 +70,8 @@ ia64_do_page_fault (unsigned long address, unsigned long isr, struct pt_regs *re
>   	mask = ((((isr >> IA64_ISR_X_BIT) & 1UL) << VM_EXEC_BIT)
>   		| (((isr >> IA64_ISR_W_BIT) & 1UL) << VM_WRITE_BIT));
>   
> -	/* mmap_sem is performance critical.... */
> -	prefetchw(&mm->mmap_sem);
> +	/* mmap_lock is performance critical.... */
> +	prefetchw(&mm->mmap_lock);
>   
>   	/*
>   	 * If we're in an interrupt or have no user context, we must not take the fault..
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 181f66b9049f..35f530f9dfc0 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -1522,7 +1522,7 @@ dotraplinkage void
>   do_page_fault(struct pt_regs *regs, unsigned long hw_error_code,
>   		unsigned long address)
>   {
> -	prefetchw(&current->mm->mmap_sem);
> +	prefetchw(&current->mm->mmap_lock);
>   	trace_page_fault_entries(regs, hw_error_code, address);
>   
>   	if (unlikely(kmmio_fault(regs, address)))
> diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem.c b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
> index dc9ef302f517..701f3995f621 100644
> --- a/drivers/gpu/drm/etnaviv/etnaviv_gem.c
> +++ b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
> @@ -661,7 +661,7 @@ static int etnaviv_gem_userptr_get_pages(struct etnaviv_gem_object *etnaviv_obj)
>   	struct etnaviv_gem_userptr *userptr = &etnaviv_obj->userptr;
>   	int ret, pinned = 0, npages = etnaviv_obj->base.size >> PAGE_SHIFT;
>   
> -	might_lock_read(&current->mm->mmap_sem);
> +	might_lock_read(&current->mm->mmap_lock);

Why not a mm_might_lock_read() new API to hide the mmap_lock, and add it to the 
previous patch?

>   
>   	if (userptr->mm != current->mm)
>   		return -EPERM;
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 4aba6c0c2ba8..d13b90399c16 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -436,7 +436,7 @@ struct mm_struct {
>   		spinlock_t page_table_lock; /* Protects page tables and some
>   					     * counters
>   					     */
> -		struct rw_semaphore mmap_sem;
> +		struct rw_semaphore mmap_lock;
>   
>   		struct list_head mmlist; /* List of maybe swapped mm's.	These
>   					  * are globally strung together off
> diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
> index 5bf7cee5d93b..9dc632add390 100644
> --- a/include/linux/mmap_lock.h
> +++ b/include/linux/mmap_lock.h
> @@ -4,67 +4,67 @@
>   #include <linux/mmdebug.h>
>   
>   #define MMAP_LOCK_INITIALIZER(name) \
> -	.mmap_sem = __RWSEM_INITIALIZER(name.mmap_sem),
> +	.mmap_lock = __RWSEM_INITIALIZER(name.mmap_lock),
>   
>   static inline void mmap_init_lock(struct mm_struct *mm)
>   {
> -	init_rwsem(&mm->mmap_sem);
> +	init_rwsem(&mm->mmap_lock);
>   }
>   
>   static inline void mmap_write_lock(struct mm_struct *mm)
>   {
> -	down_write(&mm->mmap_sem);
> +	down_write(&mm->mmap_lock);
>   }
>   
>   static inline void mmap_write_lock_nested(struct mm_struct *mm, int subclass)
>   {
> -	down_write_nested(&mm->mmap_sem, subclass);
> +	down_write_nested(&mm->mmap_lock, subclass);
>   }
>   
>   static inline int mmap_write_lock_killable(struct mm_struct *mm)
>   {
> -	return down_write_killable(&mm->mmap_sem);
> +	return down_write_killable(&mm->mmap_lock);
>   }
>   
>   static inline bool mmap_write_trylock(struct mm_struct *mm)
>   {
> -	return down_write_trylock(&mm->mmap_sem) != 0;
> +	return down_write_trylock(&mm->mmap_lock) != 0;
>   }
>   
>   static inline void mmap_write_unlock(struct mm_struct *mm)
>   {
> -	up_write(&mm->mmap_sem);
> +	up_write(&mm->mmap_lock);
>   }
>   
>   static inline void mmap_write_downgrade(struct mm_struct *mm)
>   {
> -	downgrade_write(&mm->mmap_sem);
> +	downgrade_write(&mm->mmap_lock);
>   }
>   
>   static inline void mmap_read_lock(struct mm_struct *mm)
>   {
> -	down_read(&mm->mmap_sem);
> +	down_read(&mm->mmap_lock);
>   }
>   
>   static inline int mmap_read_lock_killable(struct mm_struct *mm)
>   {
> -	return down_read_killable(&mm->mmap_sem);
> +	return down_read_killable(&mm->mmap_lock);
>   }
>   
>   static inline bool mmap_read_trylock(struct mm_struct *mm)
>   {
> -	return down_read_trylock(&mm->mmap_sem) != 0;
> +	return down_read_trylock(&mm->mmap_lock) != 0;
>   }
>   
>   static inline void mmap_read_unlock(struct mm_struct *mm)
>   {
> -	up_read(&mm->mmap_sem);
> +	up_read(&mm->mmap_lock);
>   }
>   
>   static inline bool mmap_read_trylock_non_owner(struct mm_struct *mm)
>   {
> -	if (down_read_trylock(&mm->mmap_sem)) {
> -		rwsem_release(&mm->mmap_sem.dep_map, _RET_IP_);
> +	if (down_read_trylock(&mm->mmap_lock)) {
> +		rwsem_release(&mm->mmap_lock.dep_map, _RET_IP_);
>   		return true;
>   	}
>   	return false;
> @@ -72,19 +72,19 @@ static inline bool mmap_read_trylock_non_owner(struct mm_struct *mm)
>   
>   static inline void mmap_read_unlock_non_owner(struct mm_struct *mm)
>   {
> -	up_read_non_owner(&mm->mmap_sem);
> +	up_read_non_owner(&mm->mmap_lock);
>   }
>   
>   static inline void mmap_assert_locked(struct mm_struct *mm)
>   {
> -	VM_BUG_ON_MM(!lockdep_is_held_type(&mm->mmap_sem, -1), mm);
> -	VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm);
> +	VM_BUG_ON_MM(!lockdep_is_held_type(&mm->mmap_lock, -1), mm);
> +	VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm);
>   }
>   
>   static inline void mmap_assert_write_locked(struct mm_struct *mm)
>   {
> -	VM_BUG_ON_MM(!lockdep_is_held_type(&mm->mmap_sem, 0), mm);
> -	VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm);
> +	VM_BUG_ON_MM(!lockdep_is_held_type(&mm->mmap_lock, 0), mm);
> +	VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_lock), mm);
>   }
>   
>   #endif /* _LINUX_MMAP_LOCK_H */
> diff --git a/mm/memory.c b/mm/memory.c
> index 20f98ea8968e..c2963e7affa9 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4811,7 +4811,7 @@ void __might_fault(const char *file, int line)
>   	__might_sleep(file, line, 0);
>   #if defined(CONFIG_DEBUG_ATOMIC_SLEEP)
>   	if (current->mm)
> -		might_lock_read(&current->mm->mmap_sem);
> +		might_lock_read(&current->mm->mmap_lock);
>   #endif
>   }
>   EXPORT_SYMBOL(__might_fault);
> diff --git a/mm/mmap.c b/mm/mmap.c
> index 2f4ffccc5972..80a47031d5db 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -3474,7 +3474,7 @@ static void vm_lock_anon_vma(struct mm_struct *mm, struct anon_vma *anon_vma)
>   		 * The LSB of head.next can't change from under us
>   		 * because we hold the mm_all_locks_mutex.
>   		 */
> -		down_write_nest_lock(&anon_vma->root->rwsem, &mm->mmap_sem);
> +		down_write_nest_lock(&anon_vma->root->rwsem, &mm->mmap_lock);
>   		/*
>   		 * We can safely modify head.next after taking the
>   		 * anon_vma->root->rwsem. If some other vma in this mm shares
> @@ -3504,7 +3504,7 @@ static void vm_lock_mapping(struct mm_struct *mm, struct address_space *mapping)
>   		 */
>   		if (test_and_set_bit(AS_MM_ALL_LOCKS, &mapping->flags))
>   			BUG();
> -		down_write_nest_lock(&mapping->i_mmap_rwsem, &mm->mmap_sem);
> +		down_write_nest_lock(&mapping->i_mmap_rwsem, &mm->mmap_lock);
>   	}
>   }
>   
> diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
> index 24eb9d1ed0a7..2f348b6c9c9a 100644
> --- a/mm/mmu_notifier.c
> +++ b/mm/mmu_notifier.c
> @@ -983,7 +983,7 @@ int mmu_interval_notifier_insert(struct mmu_interval_notifier *interval_sub,
>   	struct mmu_notifier_subscriptions *subscriptions;
>   	int ret;
>   
> -	might_lock(&mm->mmap_sem);
> +	might_lock(&mm->mmap_lock);

Same here with a new mm_might_lock()?

>   
>   	subscriptions = smp_load_acquire(&mm->notifier_subscriptions);
>   	if (!subscriptions || !subscriptions->has_itree) {
>