[PATCH v2 0/5] read proc/pid/smaps_rollup under per-vma lock

[Suren Baghdasaryan <surenb@google.com>]

proc/pid/smaps_rollup can be read using the combination of RCU and
VMA read locks, similar to proc/pid/{maps|smaps|numa_maps}. RCU is
required to safely traverse the VMA tree and VMA lock stabilizes the
VMA being processed and the pagetable walk.
Note that we have to keep the logic to drop mmap_lock on contention
because even when using per-VMA locks we might have to fall back to
holding the mmap_lock.

The first 3 patches are cleanups making later change simpler. The main
change is in patch 4. Patch 5 extends existing proc-maps-race tearing
test to verify smaps_rollup content.

Changes since v1 [1]
- removed helper functions which are not needed after per-VMA locks
became unconditional in [2];
- added a cover letter, per Lorenzo Stoakes and David Hildenbrand;
- removed is_mmap_lock_contended() as it's no more needed after [2],
per David Hildenbrand;
- fixed typos, per Lorenzo Stoakes and David Hildenbrand;
- refactored duplicate error checks, per Lorenzo Stoakes;
- eliminated special case of start=0 in smap_gather_stats(),
per Lorenzo Stoakes;
- updated comments, per Lorenzo Stoakes;
- moved original comment about 4 possible cases when mmap lock is
dropped into patch 4 changelog;
- added smaps_rollup testing into proc-maps-race test.

[1] https://lore.kernel.org/all/20260606015729.1837935-1-surenb@google.com/
[2] https://lore.kernel.org/all/20260813193433.3318288-1-surenb@google.com/

Suren Baghdasaryan (5):
  proc/task_mmu: remove unnecessary helpers
  proc/task_mmu: remove unnecessary inlines in function definitions
  proc/task_mmu: remove special-casing of smap_gather_stats() start
    parameter
  proc/task_mmu: read proc/pid/smaps_rollup under per-vma lock
  selftests/proc: add /proc/pid/smaps_rollup tearing tests

 fs/proc/task_mmu.c                            | 280 +++++++-----------
 tools/testing/selftests/proc/proc-maps-race.c | 187 +++++++++++-
 2 files changed, 291 insertions(+), 176 deletions(-)


base-commit: e3fc12b08aadde9cec7b3799ac0e0c9a1aa245c4
-- 
2.55.0.979.g7e5102b832-goog