| Message ID | 20201026105818.2585306-6-daniel.vetter@ffwll.ch (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | follow_pfn and other iomap races | expand |
Hi Daniel, On Mon, Oct 26, 2020 at 11:58:08AM +0100, Daniel Vetter wrote: > This is used by media/videbuf2 for persistent dma mappings, not just > for a single dma operation and then freed again, so needs > FOLL_LONGTERM. > > Unfortunately current pup_locked doesn't support FOLL_LONGTERM due to > locking issues. Rework the code to pull the pup path out from the > mmap_sem critical section as suggested by Jason. > > By relying entirely on the vma checks in pin_user_pages and follow_pfn > (for vm_flags and vma_is_fsdax) we can also streamline the code a lot. > > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> > Cc: Jason Gunthorpe <jgg@ziepe.ca> > Cc: Pawel Osciak <pawel@osciak.com> > Cc: Marek Szyprowski <m.szyprowski@samsung.com> > Cc: Kyungmin Park <kyungmin.park@samsung.com> > Cc: Tomasz Figa <tfiga@chromium.org> > Cc: Mauro Carvalho Chehab <mchehab@kernel.org> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: John Hubbard <jhubbard@nvidia.com> > Cc: Jérôme Glisse <jglisse@redhat.com> > Cc: Jan Kara <jack@suse.cz> > Cc: Dan Williams <dan.j.williams@intel.com> > Cc: linux-mm@kvack.org > Cc: linux-arm-kernel@lists.infradead.org > Cc: linux-samsung-soc@vger.kernel.org > Cc: linux-media@vger.kernel.org > Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> > -- > v2: Streamline the code and further simplify the loop checks (Jason) > --- > mm/frame_vector.c | 50 ++++++++++++++--------------------------------- > 1 file changed, 15 insertions(+), 35 deletions(-) > Thank you for the patch. Please see my comments inline. > diff --git a/mm/frame_vector.c b/mm/frame_vector.c > index 10f82d5643b6..d44779e56313 100644 > --- a/mm/frame_vector.c > +++ b/mm/frame_vector.c > @@ -38,7 +38,6 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames, > struct vm_area_struct *vma; > int ret = 0; > int err; > - int locked; > > if (nr_frames == 0) > return 0; > @@ -48,40 +47,25 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames, > > start = untagged_addr(start); > > - mmap_read_lock(mm); > - locked = 1; > - vma = find_vma_intersection(mm, start, start + 1); > - if (!vma) { > - ret = -EFAULT; > - goto out; > - } > - > - /* > - * While get_vaddr_frames() could be used for transient (kernel > - * controlled lifetime) pinning of memory pages all current > - * users establish long term (userspace controlled lifetime) > - * page pinning. Treat get_vaddr_frames() like > - * get_user_pages_longterm() and disallow it for filesystem-dax > - * mappings. > - */ > - if (vma_is_fsdax(vma)) { > - ret = -EOPNOTSUPP; > - goto out; > - } > - > - if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) { > + ret = pin_user_pages_fast(start, nr_frames, > + FOLL_FORCE | FOLL_WRITE | FOLL_LONGTERM, > + (struct page **)(vec->ptrs)); > + if (ret > 0) { > vec->got_ref = true; > vec->is_pfns = false; > - ret = pin_user_pages_locked(start, nr_frames, > - gup_flags, (struct page **)(vec->ptrs), &locked); Should we drop the gup_flags argument, since it's ignored now? > - goto out; > + goto out_unlocked; > } > Should we initialize ret with 0 here, since pin_user_pages_fast() can return a negative error code, but below we use it as a counter for the looked up frames? Best regards, Tomasz > + mmap_read_lock(mm); > vec->got_ref = false; > vec->is_pfns = true; > do { > unsigned long *nums = frame_vector_pfns(vec); > > + vma = find_vma_intersection(mm, start, start + 1); > + if (!vma) > + break; > + > while (ret < nr_frames && start + PAGE_SIZE <= vma->vm_end) { > err = follow_pfn(vma, start, &nums[ret]); > if (err) { > @@ -92,17 +76,13 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames, > start += PAGE_SIZE; > ret++; > } > - /* > - * We stop if we have enough pages or if VMA doesn't completely > - * cover the tail page. > - */ > - if (ret >= nr_frames || start < vma->vm_end) > + /* Bail out if VMA doesn't completely cover the tail page. */ > + if (start < vma->vm_end) > break; > - vma = find_vma_intersection(mm, start, start + 1); > - } while (vma && vma->vm_flags & (VM_IO | VM_PFNMAP)); > + } while (ret < nr_frames); > out: > - if (locked) > - mmap_read_unlock(mm); > + mmap_read_unlock(mm); > +out_unlocked: > if (!ret) > ret = -EFAULT; > if (ret > 0) > -- > 2.28.0 >
On Mon, Oct 26, 2020 at 11:15 PM Tomasz Figa <tfiga@chromium.org> wrote: > > Hi Daniel, > > On Mon, Oct 26, 2020 at 11:58:08AM +0100, Daniel Vetter wrote: > > This is used by media/videbuf2 for persistent dma mappings, not just > > for a single dma operation and then freed again, so needs > > FOLL_LONGTERM. > > > > Unfortunately current pup_locked doesn't support FOLL_LONGTERM due to > > locking issues. Rework the code to pull the pup path out from the > > mmap_sem critical section as suggested by Jason. > > > > By relying entirely on the vma checks in pin_user_pages and follow_pfn > > (for vm_flags and vma_is_fsdax) we can also streamline the code a lot. > > > > Signed-off-by: Daniel Vetter <daniel.vetter@intel.com> > > Cc: Jason Gunthorpe <jgg@ziepe.ca> > > Cc: Pawel Osciak <pawel@osciak.com> > > Cc: Marek Szyprowski <m.szyprowski@samsung.com> > > Cc: Kyungmin Park <kyungmin.park@samsung.com> > > Cc: Tomasz Figa <tfiga@chromium.org> > > Cc: Mauro Carvalho Chehab <mchehab@kernel.org> > > Cc: Andrew Morton <akpm@linux-foundation.org> > > Cc: John Hubbard <jhubbard@nvidia.com> > > Cc: Jérôme Glisse <jglisse@redhat.com> > > Cc: Jan Kara <jack@suse.cz> > > Cc: Dan Williams <dan.j.williams@intel.com> > > Cc: linux-mm@kvack.org > > Cc: linux-arm-kernel@lists.infradead.org > > Cc: linux-samsung-soc@vger.kernel.org > > Cc: linux-media@vger.kernel.org > > Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> > > -- > > v2: Streamline the code and further simplify the loop checks (Jason) > > --- > > mm/frame_vector.c | 50 ++++++++++++++--------------------------------- > > 1 file changed, 15 insertions(+), 35 deletions(-) > > > > Thank you for the patch. Please see my comments inline. > > > diff --git a/mm/frame_vector.c b/mm/frame_vector.c > > index 10f82d5643b6..d44779e56313 100644 > > --- a/mm/frame_vector.c > > +++ b/mm/frame_vector.c > > @@ -38,7 +38,6 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames, > > struct vm_area_struct *vma; > > int ret = 0; > > int err; > > - int locked; > > > > if (nr_frames == 0) > > return 0; > > @@ -48,40 +47,25 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames, > > > > start = untagged_addr(start); > > > > - mmap_read_lock(mm); > > - locked = 1; > > - vma = find_vma_intersection(mm, start, start + 1); > > - if (!vma) { > > - ret = -EFAULT; > > - goto out; > > - } > > - > > - /* > > - * While get_vaddr_frames() could be used for transient (kernel > > - * controlled lifetime) pinning of memory pages all current > > - * users establish long term (userspace controlled lifetime) > > - * page pinning. Treat get_vaddr_frames() like > > - * get_user_pages_longterm() and disallow it for filesystem-dax > > - * mappings. > > - */ > > - if (vma_is_fsdax(vma)) { > > - ret = -EOPNOTSUPP; > > - goto out; > > - } > > - > > - if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) { > > + ret = pin_user_pages_fast(start, nr_frames, > > + FOLL_FORCE | FOLL_WRITE | FOLL_LONGTERM, > > + (struct page **)(vec->ptrs)); > > + if (ret > 0) { > > vec->got_ref = true; > > vec->is_pfns = false; > > - ret = pin_user_pages_locked(start, nr_frames, > > - gup_flags, (struct page **)(vec->ptrs), &locked); > > Should we drop the gup_flags argument, since it's ignored now? Hm right I think an earlier version even had that, but then I moved to inlining the functionality in all the places it's used. I'll drop the gup flag. > > - goto out; > > + goto out_unlocked; > > } > > > > Should we initialize ret with 0 here, since pin_user_pages_fast() can > return a negative error code, but below we use it as a counter for the > looked up frames? Indeed, that's a bug. Will fix for v5. -Daniel > Best regards, > Tomasz > > > + mmap_read_lock(mm); > > vec->got_ref = false; > > vec->is_pfns = true; > > do { > > unsigned long *nums = frame_vector_pfns(vec); > > > > + vma = find_vma_intersection(mm, start, start + 1); > > + if (!vma) > > + break; > > + > > while (ret < nr_frames && start + PAGE_SIZE <= vma->vm_end) { > > err = follow_pfn(vma, start, &nums[ret]); > > if (err) { > > @@ -92,17 +76,13 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames, > > start += PAGE_SIZE; > > ret++; > > } > > - /* > > - * We stop if we have enough pages or if VMA doesn't completely > > - * cover the tail page. > > - */ > > - if (ret >= nr_frames || start < vma->vm_end) > > + /* Bail out if VMA doesn't completely cover the tail page. */ > > + if (start < vma->vm_end) > > break; > > - vma = find_vma_intersection(mm, start, start + 1); > > - } while (vma && vma->vm_flags & (VM_IO | VM_PFNMAP)); > > + } while (ret < nr_frames); > > out: > > - if (locked) > > - mmap_read_unlock(mm); > > + mmap_read_unlock(mm); > > +out_unlocked: > > if (!ret) > > ret = -EFAULT; > > if (ret > 0) > > -- > > 2.28.0 > >
diff --git a/mm/frame_vector.c b/mm/frame_vector.c index 10f82d5643b6..d44779e56313 100644 --- a/mm/frame_vector.c +++ b/mm/frame_vector.c @@ -38,7 +38,6 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames, struct vm_area_struct *vma; int ret = 0; int err; - int locked; if (nr_frames == 0) return 0; @@ -48,40 +47,25 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames, start = untagged_addr(start); - mmap_read_lock(mm); - locked = 1; - vma = find_vma_intersection(mm, start, start + 1); - if (!vma) { - ret = -EFAULT; - goto out; - } - - /* - * While get_vaddr_frames() could be used for transient (kernel - * controlled lifetime) pinning of memory pages all current - * users establish long term (userspace controlled lifetime) - * page pinning. Treat get_vaddr_frames() like - * get_user_pages_longterm() and disallow it for filesystem-dax - * mappings. - */ - if (vma_is_fsdax(vma)) { - ret = -EOPNOTSUPP; - goto out; - } - - if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) { + ret = pin_user_pages_fast(start, nr_frames, + FOLL_FORCE | FOLL_WRITE | FOLL_LONGTERM, + (struct page **)(vec->ptrs)); + if (ret > 0) { vec->got_ref = true; vec->is_pfns = false; - ret = pin_user_pages_locked(start, nr_frames, - gup_flags, (struct page **)(vec->ptrs), &locked); - goto out; + goto out_unlocked; } + mmap_read_lock(mm); vec->got_ref = false; vec->is_pfns = true; do { unsigned long *nums = frame_vector_pfns(vec); + vma = find_vma_intersection(mm, start, start + 1); + if (!vma) + break; + while (ret < nr_frames && start + PAGE_SIZE <= vma->vm_end) { err = follow_pfn(vma, start, &nums[ret]); if (err) { @@ -92,17 +76,13 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames, start += PAGE_SIZE; ret++; } - /* - * We stop if we have enough pages or if VMA doesn't completely - * cover the tail page. - */ - if (ret >= nr_frames || start < vma->vm_end) + /* Bail out if VMA doesn't completely cover the tail page. */ + if (start < vma->vm_end) break; - vma = find_vma_intersection(mm, start, start + 1); - } while (vma && vma->vm_flags & (VM_IO | VM_PFNMAP)); + } while (ret < nr_frames); out: - if (locked) - mmap_read_unlock(mm); + mmap_read_unlock(mm); +out_unlocked: if (!ret) ret = -EFAULT; if (ret > 0)