Re: [PATCH v2 4/5] binder: Remove mmap_lock fallback
From: Suren Baghdasaryan <surenb@google.com>
Date: 2026-06-11 20:40:50
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On Wed, Jun 10, 2026 at 4:04 PM Dave Hansen [off-list ref] wrote:
From: Dave Hansen <dave.hansen@linux.intel.com> Previously, the per-VMA locking could fail in the face of writers which necessitate a fallback to mmap_lock. The new vma_start_read_unlocked() will wait for writers instead of failing. Use the new helper. Wait for writers. Remove the fallback to mmap_lock.
Nice!
quoted hunk ↗ jump to hunk
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Acked-by: Lorenzo Stoakes <ljs@kernel.org> Reviewed-by: Suren Baghdasaryan <surenb@google.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: "Liam R. Howlett" <redacted> Cc: Vlastimil Babka <vbabka@kernel.org> Cc: Shakeel Butt <shakeel.butt@linux.dev> Cc: linux-mm@kvack.org Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Arve Hjønnevåg <arve@android.com> Cc: Todd Kjos <tkjos@android.com> Cc: Christian Brauner <christian@brauner.io> Cc: Carlos Llamas <cmllamas@google.com> Cc: Alice Ryhl <aliceryhl@google.com> Cc: "David S. Miller" <davem@davemloft.net> Cc: David Ahern <dsahern@kernel.org> Cc: netdev@vger.kernel.org --- b/drivers/android/binder_alloc.c | 17 +++++------------ 1 file changed, 5 insertions(+), 12 deletions(-) diff -puN drivers/android/binder_alloc.c~binder-vma-waiter drivers/android/binder_alloc.c--- a/drivers/android/binder_alloc.c~binder-vma-waiter 2026-06-10 15:57:56.419452721 -0700 +++ b/drivers/android/binder_alloc.c 2026-06-10 15:57:56.423452863 -0700@@ -259,21 +259,14 @@ static int binder_page_insert(struct bin struct vm_area_struct *vma; int ret = -ESRCH; - /* attempt per-vma lock first */ - vma = lock_vma_under_rcu(mm, addr); - if (vma) { - if (binder_alloc_is_mapped(alloc)) - ret = vm_insert_page(vma, addr, page); - vma_end_read(vma); + vma = vma_start_read_unlocked(mm, addr); + if (!vma) return ret; - } - /* fall back to mmap_lock */ - mmap_read_lock(mm); - vma = vma_lookup(mm, addr); - if (vma && binder_alloc_is_mapped(alloc)) + if (binder_alloc_is_mapped(alloc)) ret = vm_insert_page(vma, addr, page); - mmap_read_unlock(mm); + + vma_end_read(vma); return ret; }_