| Message ID | 20230804152724.3090321-6-surenb@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | make vma locking more obvious | expand |
@akpm can you fix this up? On Fri, Aug 4, 2023 at 5:27 PM Suren Baghdasaryan <surenb@google.com> wrote: > While it's not strictly necessary to lock a newly created vma before > adding it into the vma tree (as long as no further changes are performed > to it), it seems like a good policy to lock it and prevent accidental > changes after it becomes visible to the page faults. Lock the vma before > adding it into the vma tree. > > Suggested-by: Jann Horn <jannh@google.com> > Signed-off-by: Suren Baghdasaryan <surenb@google.com> > Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com> > --- > mm/mmap.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/mm/mmap.c b/mm/mmap.c > index 3937479d0e07..850a39dee075 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -412,6 +412,8 @@ static int vma_link(struct mm_struct *mm, struct vm_area_struct *vma) > if (vma_iter_prealloc(&vmi)) > return -ENOMEM; > > + vma_start_write(vma); > + > if (vma->vm_file) { > mapping = vma->vm_file->f_mapping; > i_mmap_lock_write(mapping); Something went wrong when this part of the patch was applied, because of a conflict with "mm/mmap: move vma operations to mm_struct out of the critical section of file mapping lock"; see how this patch ended up in the mm tree: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/commit/?id=26cb4dafc13871ab68a4fb480ca1e19381cff392 > @@ -403,6 +403,8 @@ static int vma_link(struct mm_struct *mm, struct vm_area_struct *vma) > > vma_iter_store(&vmi, vma); > > + vma_start_write(vma); > + > if (vma->vm_file) { > mapping = vma->vm_file->f_mapping; > i_mmap_lock_write(mapping); The "vma_start_write()" has to be ordered before the "vma_iter_store(&vmi, vma)".
On Mon, 14 Aug 2023 16:54:01 +0200 Jann Horn <jannh@google.com> wrote: > > @@ -403,6 +403,8 @@ static int vma_link(struct mm_struct *mm, struct vm_area_struct *vma) > > > > vma_iter_store(&vmi, vma); > > > > + vma_start_write(vma); > > + > > if (vma->vm_file) { > > mapping = vma->vm_file->f_mapping; > > i_mmap_lock_write(mapping); > > The "vma_start_write()" has to be ordered before the > "vma_iter_store(&vmi, vma)". Thanks. This? --- a/mm/mmap.c~mm-always-lock-new-vma-before-inserting-into-vma-tree-fix +++ a/mm/mmap.c @@ -401,10 +401,10 @@ static int vma_link(struct mm_struct *mm if (vma_iter_prealloc(&vmi, vma)) return -ENOMEM; - vma_iter_store(&vmi, vma); - vma_start_write(vma); + vma_iter_store(&vmi, vma); + if (vma->vm_file) { mapping = vma->vm_file->f_mapping; i_mmap_lock_write(mapping);
* Andrew Morton <akpm@linux-foundation.org> [230814 15:15]: > On Mon, 14 Aug 2023 16:54:01 +0200 Jann Horn <jannh@google.com> wrote: > > > > @@ -403,6 +403,8 @@ static int vma_link(struct mm_struct *mm, struct vm_area_struct *vma) > > > > > > vma_iter_store(&vmi, vma); > > > > > > + vma_start_write(vma); > > > + > > > if (vma->vm_file) { > > > mapping = vma->vm_file->f_mapping; > > > i_mmap_lock_write(mapping); > > > > The "vma_start_write()" has to be ordered before the > > "vma_iter_store(&vmi, vma)". > > Thanks. This? Yes, this looks good. > > > --- a/mm/mmap.c~mm-always-lock-new-vma-before-inserting-into-vma-tree-fix > +++ a/mm/mmap.c > @@ -401,10 +401,10 @@ static int vma_link(struct mm_struct *mm > if (vma_iter_prealloc(&vmi, vma)) > return -ENOMEM; > > - vma_iter_store(&vmi, vma); > - > vma_start_write(vma); > > + vma_iter_store(&vmi, vma); > + > if (vma->vm_file) { > mapping = vma->vm_file->f_mapping; > i_mmap_lock_write(mapping); > _ >
On Mon, Aug 14, 2023 at 9:15 PM Andrew Morton <akpm@linux-foundation.org> wrote: > On Mon, 14 Aug 2023 16:54:01 +0200 Jann Horn <jannh@google.com> wrote: > > > > @@ -403,6 +403,8 @@ static int vma_link(struct mm_struct *mm, struct vm_area_struct *vma) > > > > > > vma_iter_store(&vmi, vma); > > > > > > + vma_start_write(vma); > > > + > > > if (vma->vm_file) { > > > mapping = vma->vm_file->f_mapping; > > > i_mmap_lock_write(mapping); > > > > The "vma_start_write()" has to be ordered before the > > "vma_iter_store(&vmi, vma)". > > Thanks. This? > > > --- a/mm/mmap.c~mm-always-lock-new-vma-before-inserting-into-vma-tree-fix > +++ a/mm/mmap.c > @@ -401,10 +401,10 @@ static int vma_link(struct mm_struct *mm > if (vma_iter_prealloc(&vmi, vma)) > return -ENOMEM; > > - vma_iter_store(&vmi, vma); > - > vma_start_write(vma); > > + vma_iter_store(&vmi, vma); > + > if (vma->vm_file) { > mapping = vma->vm_file->f_mapping; > i_mmap_lock_write(mapping); Yes, thanks, that looks good.
On Mon, Aug 14, 2023 at 1:02 PM Jann Horn <jannh@google.com> wrote: > > On Mon, Aug 14, 2023 at 9:15 PM Andrew Morton <akpm@linux-foundation.org> wrote: > > On Mon, 14 Aug 2023 16:54:01 +0200 Jann Horn <jannh@google.com> wrote: > > > > > > @@ -403,6 +403,8 @@ static int vma_link(struct mm_struct *mm, struct vm_area_struct *vma) > > > > > > > > vma_iter_store(&vmi, vma); > > > > > > > > + vma_start_write(vma); > > > > + > > > > if (vma->vm_file) { > > > > mapping = vma->vm_file->f_mapping; > > > > i_mmap_lock_write(mapping); > > > > > > The "vma_start_write()" has to be ordered before the > > > "vma_iter_store(&vmi, vma)". > > > > Thanks. This? > > > > > > --- a/mm/mmap.c~mm-always-lock-new-vma-before-inserting-into-vma-tree-fix > > +++ a/mm/mmap.c > > @@ -401,10 +401,10 @@ static int vma_link(struct mm_struct *mm > > if (vma_iter_prealloc(&vmi, vma)) > > return -ENOMEM; > > > > - vma_iter_store(&vmi, vma); > > - > > vma_start_write(vma); > > > > + vma_iter_store(&vmi, vma); > > + > > if (vma->vm_file) { > > mapping = vma->vm_file->f_mapping; > > i_mmap_lock_write(mapping); > > Yes, thanks, that looks good. Ack. Thanks!
diff --git a/mm/mmap.c b/mm/mmap.c index 3937479d0e07..850a39dee075 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -412,6 +412,8 @@ static int vma_link(struct mm_struct *mm, struct vm_area_struct *vma) if (vma_iter_prealloc(&vmi)) return -ENOMEM; + vma_start_write(vma); + if (vma->vm_file) { mapping = vma->vm_file->f_mapping; i_mmap_lock_write(mapping); @@ -477,7 +479,8 @@ static inline void vma_prepare(struct vma_prepare *vp) vma_start_write(vp->vma); if (vp->adj_next) vma_start_write(vp->adj_next); - /* vp->insert is always a newly created VMA, no need for locking */ + if (vp->insert) + vma_start_write(vp->insert); if (vp->remove) vma_start_write(vp->remove); if (vp->remove2) @@ -3098,6 +3101,7 @@ static int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *vma, vma->vm_pgoff = addr >> PAGE_SHIFT; vm_flags_init(vma, flags); vma->vm_page_prot = vm_get_page_prot(flags); + vma_start_write(vma); if (vma_iter_store_gfp(vmi, vma, GFP_KERNEL)) goto mas_store_fail; @@ -3345,7 +3349,6 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap, get_file(new_vma->vm_file); if (new_vma->vm_ops && new_vma->vm_ops->open) new_vma->vm_ops->open(new_vma); - vma_start_write(new_vma); if (vma_link(mm, new_vma)) goto out_vma_link; *need_rmap_locks = false;