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Simplify some of the per-VMA lock users now that they can rely on them being always available. Binder and networking folks: Your code is the target of the cleanups. I'm cc'ing you now on v2 because there's emerging consensus on the mm side that the approach here is sane. I'm not quite sure how this pile would get merged, but ack/review tags would be appreciated if this looks good to you. Longer version: When working on some x86 shadow stack code, it was a real pain to avoid causing recursive locking problems with mmap_lock. One way to avoid those was to avoid mmap_lock and use per-VMA locks instead. They are great, but they are not available in all configs which makes them unusable in generic code, or if you want to completely avoid mmap_lock. Make per-VMA locks available in all configs. Right now, they are only available on select architectures when SMP and MMU are enabled. But all of the primitives that per-VMA locks are built on (RCU, maple trees, refcounts) work just fine without SMP or MMU. The only real downside is that making VMAs a wee bit bigger on !MMU and !SMP builds. The upside is much cleaner code, lower complexity and less #ifdeffery. Clean up a binder VMA locking site now that it can rely on per-VMA locks. Building on top of universally-available per-VMA locks, introduce a new helper. Since the new API does not require callers to have a fallback to mmap_lock, it's much easier to use. Callers can potentially replace this very common kernel idiom: mmap_read_lock(mm); vma =3D vma_lookup() // fiddle with vma mmap_read_unlock(mm); with: vma =3D vma_start_read_unlocked(mm, address); // fiddle with vma vma_end_read(vma); Which avoids mmap_lock entirely in the fast path. Use that new API for another binder site and one in the TCP code. Cc: Suren Baghdasaryan Cc: Andrew Morton Cc: "Liam R. Howlett" Cc: Lorenzo Stoakes Cc: Vlastimil Babka Cc: Jann Horn Cc: Shakeel Butt Cc: linux-mm@kvack.org Cc: Greg Kroah-Hartman Cc: Arve Hj=C3=B8nnev=C3=A5g Cc: Todd Kjos Cc: Christian Brauner Cc: Carlos Llamas Cc: Alice Ryhl Cc: "David S. Miller" Cc: David Ahern Cc: netdev@vger.kernel.org Changes from v3 [2]: Patch 1: - Restored a comment in Kconfig, per Vlastimil Babka - Removed extra braces in mm.rs, per Vlastimil Babka - Removed obsolete comment in mm.rs, per Sashiko - Updated patch description to explain considerations for !CONFIG_MMU - Changed stack_map_lock_vma() to keep mmap_lock if !CONFIG_MMU - Changed bpf_iter_task_vma_new() to bail out if !CONFIG_MMU - Added !CONFIG_MMU versions of vma_mark_attached(), vma_mark_detached(), vma_start_write(), vma_start_write_killable(), vma_assert_attached() and vma_assert_write_locked() Patch 2: - Move binder_alloc_is_mapped() check to only protect zap_vma_range() and make error handling consistent, per Alice Ryhl and Lorenzo Stoakes Patch 3: - Added Suggested-by, per Lorenzo Stoakes - Updated the comments for vma_start_read_unlocked(), per Lorenzo Stoakes and Vlastimil Babka - Updated the patch description, per Vlastimil Babka and Lorenzo Stoakes Patch 4: - Updated comments for vma_start_read_unlocked() Rust version to be consistent with C, per Lorenzo Stoakes - Added Reviewed-by and Acked-by, per Alice Ryhl and Lorenzo Stoakes Patch 5: - Added a note in the changelog why the mmap_lock fallback removal does not affect NOMMU case Applies cleanly over mm-unstable [1] https://lore.kernel.org/all/20260610230409.A44D29FA@davehans-spike.ostc= .intel.com/ [2] https://lore.kernel.org/all/20260802215459.2769283-1-surenb@google.com/ Dave Hansen (5): mm: Make per-VMA locks available universally binder: Make shrinker rely solely on per-VMA lock mm: Add RCU-based VMA lookup helper that waits for writers binder: Remove mmap_lock fallback tcp: Remove mmap_lock fallback path arch/arm/Kconfig | 1 - arch/arm64/Kconfig | 1 - arch/loongarch/Kconfig | 1 - arch/powerpc/platforms/powernv/Kconfig | 1 - arch/powerpc/platforms/pseries/Kconfig | 1 - arch/riscv/Kconfig | 1 - arch/s390/Kconfig | 1 - arch/x86/Kconfig | 2 - drivers/android/binder/page_range.rs | 19 +----- drivers/android/binder_alloc.c | 62 +++++++---------- fs/proc/internal.h | 2 - fs/proc/task_mmu.c | 93 -------------------------- include/linux/mm.h | 12 ---- include/linux/mm_types.h | 8 +-- include/linux/mmap_lock.h | 89 ++++++++++-------------- kernel/bpf/stackmap.c | 15 ++--- kernel/bpf/task_iter.c | 2 +- kernel/fork.c | 2 - mm/Kconfig | 12 ---- mm/Kconfig.debug | 1 - mm/debug.c | 4 -- mm/init-mm.c | 2 - mm/memory.c | 2 - mm/mmap_lock.c | 59 +++++++++------- mm/pagewalk.c | 2 - mm/rmap.c | 2 - mm/userfaultfd.c | 61 ++--------------- net/ipv4/tcp.c | 31 +++------ rust/kernel/mm.rs | 57 ++++++++++------ tools/testing/vma/include/dup.h | 5 +- tools/testing/vma/vma_internal.h | 1 - 31 files changed, 157 insertions(+), 395 deletions(-) base-commit: bacc32cc7de65ffff70080a48eb294f89e434d5e --=20 2.55.0.654.g21b8a5bc05-goog