Re: [PATCH v5 19/21] ipc/shm, mm: Drop do_vma_munmap()

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

On Wed, Jul 17, 2024 at 04:07:07PM GMT, Liam R. Howlett wrote:
> From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>
>
> The do_vma_munmap() wrapper existed for callers that didn't have a vma
> iterator and needed to check the vma mseal status prior to calling the
> underlying munmap().  All callers now use a vma iterator and since the
> mseal check of can_modify_mm() has been moved to do_vmi_align_munmap()
> and the vmas are aligned, this function can just be called instead.
>
> do_vmi_align_munmap() can no longer be static as ipc/shm is using it and
> it is exported via the mm.h header.
>
> Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
> ---
>  include/linux/mm.h |  6 +++---
>  ipc/shm.c          |  8 ++++----
>  mm/mmap.c          | 33 +++++----------------------------
>  3 files changed, 12 insertions(+), 35 deletions(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 5f1075d19600..49a24c023153 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -3406,14 +3406,14 @@ extern unsigned long do_mmap(struct file *file, unsigned long addr,
>  extern int do_vmi_munmap(struct vma_iterator *vmi, struct mm_struct *mm,
>  			 unsigned long start, size_t len, struct list_head *uf,
>  			 bool unlock);
> +extern int do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
> +		    struct mm_struct *mm, unsigned long start,
> +		    unsigned long end, struct list_head *uf, bool unlock);

Going to give the same nit as Vlasta gave to me ;) which is that I believe
there's an unwritten rule that we drop the superfluous extern as we go
here.

Obviously this is not very important! :)

>  extern int do_munmap(struct mm_struct *, unsigned long, size_t,
>  		     struct list_head *uf);
>  extern int do_madvise(struct mm_struct *mm, unsigned long start, size_t len_in, int behavior);
>
>  #ifdef CONFIG_MMU
> -extern int do_vma_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
> -			 unsigned long start, unsigned long end,
> -			 struct list_head *uf, bool unlock);
>  extern int __mm_populate(unsigned long addr, unsigned long len,
>  			 int ignore_errors);
>  static inline void mm_populate(unsigned long addr, unsigned long len)
> diff --git a/ipc/shm.c b/ipc/shm.c
> index 3e3071252dac..99564c870084 100644
> --- a/ipc/shm.c
> +++ b/ipc/shm.c
> @@ -1778,8 +1778,8 @@ long ksys_shmdt(char __user *shmaddr)
>  			 */
>  			file = vma->vm_file;
>  			size = i_size_read(file_inode(vma->vm_file));
> -			do_vma_munmap(&vmi, vma, vma->vm_start, vma->vm_end,
> -				      NULL, false);
> +			do_vmi_align_munmap(&vmi, vma, mm, vma->vm_start,
> +					    vma->vm_end, NULL, false);
>  			/*
>  			 * We discovered the size of the shm segment, so
>  			 * break out of here and fall through to the next
> @@ -1803,8 +1803,8 @@ long ksys_shmdt(char __user *shmaddr)
>  		if ((vma->vm_ops == &shm_vm_ops) &&
>  		    ((vma->vm_start - addr)/PAGE_SIZE == vma->vm_pgoff) &&
>  		    (vma->vm_file == file)) {
> -			do_vma_munmap(&vmi, vma, vma->vm_start, vma->vm_end,
> -				      NULL, false);
> +			do_vmi_align_munmap(&vmi, vma, mm, vma->vm_start,
> +					    vma->vm_end, NULL, false);
>  		}
>
>  		vma = vma_next(&vmi);
> diff --git a/mm/mmap.c b/mm/mmap.c
> index a32f545d3987..ca752317adef 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -269,11 +269,12 @@ SYSCALL_DEFINE1(brk, unsigned long, brk)
>  			goto out; /* mapping intersects with an existing non-brk vma. */
>  		/*
>  		 * mm->brk must be protected by write mmap_lock.
> -		 * do_vma_munmap() will drop the lock on success,  so update it
> -		 * before calling do_vma_munmap().
> +		 * do_vmi_align_munmap() will drop the lock on success,  so
> +		 * update it before calling do_vma_munmap().
>  		 */
>  		mm->brk = brk;
> -		if (do_vma_munmap(&vmi, brkvma, newbrk, oldbrk, &uf, true))
> +		if (do_vmi_align_munmap(&vmi, brkvma, mm, newbrk, oldbrk, &uf,
> +					/* unlock = */ true))
>  			goto out;
>
>  		goto success_unlocked;
> @@ -2865,7 +2866,7 @@ static int vms_gather_munmap_vmas(struct vma_munmap_struct *vms,
>   * Return: 0 on success and drops the lock if so directed, error and leaves the
>   * lock held otherwise.
>   */
> -static int
> +int
>  do_vmi_align_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
>  		    struct mm_struct *mm, unsigned long start,
>  		    unsigned long end, struct list_head *uf, bool unlock)
> @@ -3348,30 +3349,6 @@ SYSCALL_DEFINE5(remap_file_pages, unsigned long, start, unsigned long, size,
>  	return ret;
>  }
>
> -/*
> - * do_vma_munmap() - Unmap a full or partial vma.
> - * @vmi: The vma iterator pointing at the vma
> - * @vma: The first vma to be munmapped
> - * @start: the start of the address to unmap
> - * @end: The end of the address to unmap
> - * @uf: The userfaultfd list_head
> - * @unlock: Drop the lock on success
> - *
> - * unmaps a VMA mapping when the vma iterator is already in position.
> - * Does not handle alignment.
> - *
> - * Return: 0 on success drops the lock of so directed, error on failure and will
> - * still hold the lock.
> - */
> -int do_vma_munmap(struct vma_iterator *vmi, struct vm_area_struct *vma,
> -		unsigned long start, unsigned long end, struct list_head *uf,
> -		bool unlock)
> -{
> -	struct mm_struct *mm = vma->vm_mm;
> -
> -	return do_vmi_align_munmap(vmi, vma, mm, start, end, uf, unlock);
> -}
> -
>  /*
>   * do_brk_flags() - Increase the brk vma if the flags match.
>   * @vmi: The vma iterator
> --
> 2.43.0
>

This is a nice cleanup. LGTM,

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>