* Suren Baghdasaryan <surenb@xxxxxxxxxx> [230223 16:16]: > On Thu, Feb 23, 2023 at 12:28 PM Liam R. Howlett > <Liam.Howlett@xxxxxxxxxx> wrote: > > > > > > Wait, I figured a better place to do this. > > > > init_multi_vma_prep() should vma_start_write() on any VMA that is passed > > in.. that we we catch any modifications here & in vma_merge(), which I > > think is missed in this patch set? > > Hmm. That looks like a good idea but in that case, why not do the > locking inside vma_prepare() itself? From the description of that > function it sounds like it was designed to acquire locks before VMA > modifications, so would be the ideal location for doing that. WDYT? That might be even better. I think it will result in even less code. There is also a vma_complete() which might work to call vma_end_write_all() as well? > The only concern is vma_adjust_trans_huge() being called before > vma_prepare() but I *think* that's safe because > vma_adjust_trans_huge() does its modifications after acquiring PTL > lock, which page fault handlers also have to take. Does that sound > right? I am not sure. We are certainly safe the way it is, and the PTL has to be safe for concurrent faults.. but this could alter the walk to a page table while that walk is occurring and I don't think that happens today. It might be best to leave the locking order the way you have it, unless someone can tell us it's safe? We could pass through the three extra variables that are needed to move the vma_adjust_trans_huge() call within that function as well? This would have the added benefit of having all locking grouped in the one location, but the argument list would be getting long, however we could use the struct. remove & remove2 should be be detached in vma_prepare() or vma_complete() as well? > > > > > > > * Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> [230223 15:20]: > > > Reviewed-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> > > > > > > * Suren Baghdasaryan <surenb@xxxxxxxxxx> [230216 00:18]: > > > > vma_expand and vma_shrink change VMA boundaries. Expansion might also > > > > result in freeing of an adjacent VMA. Write-lock affected VMAs to prevent > > > > concurrent page faults. > > > > > > > > Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx> > > > > --- > > > > mm/mmap.c | 5 +++++ > > > > 1 file changed, 5 insertions(+) > > > > > > > > diff --git a/mm/mmap.c b/mm/mmap.c > > > > index ec2f8d0af280..f079e5bbcd57 100644 > > > > --- a/mm/mmap.c > > > > +++ b/mm/mmap.c > > > > @@ -674,6 +674,9 @@ int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma, > > > > ret = dup_anon_vma(vma, next); > > > > if (ret) > > > > return ret; > > > > + > > > > + /* Lock the VMA before removing it */ > > > > + vma_start_write(next); > > > > } > > > > > > > > init_multi_vma_prep(&vp, vma, NULL, remove_next ? next : NULL, NULL); > > > > @@ -686,6 +689,7 @@ int vma_expand(struct vma_iterator *vmi, struct vm_area_struct *vma, > > > > if (vma_iter_prealloc(vmi)) > > > > goto nomem; > > > > > > > > + vma_start_write(vma); > > > > vma_adjust_trans_huge(vma, start, end, 0); > > > > /* VMA iterator points to previous, so set to start if necessary */ > > > > if (vma_iter_addr(vmi) != start) > > > > @@ -725,6 +729,7 @@ int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma, > > > > if (vma_iter_prealloc(vmi)) > > > > return -ENOMEM; > > > > > > > > + vma_start_write(vma); > > > > init_vma_prep(&vp, vma); > > > > vma_adjust_trans_huge(vma, start, end, 0); > > > > vma_prepare(&vp); > > > > -- > > > > 2.39.1 > > > > > > > > -- > > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@xxxxxxxxxxx. > >
