On 4/22/20 2:14 AM, Michel Lespinasse wrote:
> Add API for nested write locks and convert the few call sites doing that.
>
> Signed-off-by: Michel Lespinasse <walken@xxxxxxxxxx>
> Reviewed-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
Perhaps we could even move SINGLE_DEPTH_NESTING into the wrapper? It's unlikely
there will be a new user with a different subclass?
> ---
> arch/um/include/asm/mmu_context.h | 3 ++-
> include/linux/mmap_lock.h | 5 +++++
> kernel/fork.c | 2 +-
> 3 files changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/arch/um/include/asm/mmu_context.h b/arch/um/include/asm/mmu_context.h
> index 62262c5c7785..17ddd4edf875 100644
> --- a/arch/um/include/asm/mmu_context.h
> +++ b/arch/um/include/asm/mmu_context.h
> @@ -8,6 +8,7 @@
>
> #include <linux/sched.h>
> #include <linux/mm_types.h>
> +#include <linux/mmap_lock.h>
>
> #include <asm/mmu.h>
>
> @@ -47,7 +48,7 @@ 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, SINGLE_DEPTH_NESTING);
> uml_setup_stubs(new);
> mmap_write_unlock(new);
> }
> diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
> index 97ac53b66052..a757cb30ae77 100644
> --- a/include/linux/mmap_lock.h
> +++ b/include/linux/mmap_lock.h
> @@ -11,6 +11,11 @@ static inline void mmap_write_lock(struct mm_struct *mm)
> down_write(&mm->mmap_sem);
> }
>
> +static inline void mmap_write_lock_nested(struct mm_struct *mm, int subclass)
> +{
> + down_write_nested(&mm->mmap_sem, subclass);
> +}
> +
> static inline int mmap_write_lock_killable(struct mm_struct *mm)
> {
> return down_write_killable(&mm->mmap_sem);
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 41d3f45c058e..a5d1d20ccba7 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -499,7 +499,7 @@ static __latent_entropy int dup_mmap(struct mm_struct *mm,
> /*
> * Not linked in yet - no deadlock potential:
> */
> - down_write_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
> + mmap_write_lock_nested(mm, SINGLE_DEPTH_NESTING);
>
> /* No ordering required: file already has been exposed. */
> RCU_INIT_POINTER(mm->exe_file, get_mm_exe_file(oldmm));
>
