[RFC PATCH 0/8] make hugetlb put_page safe for all calling contexts

[Mike Kravetz]

This effort is the result a recent bug report [1].  In subsequent
discussions [2], it was deemed necessary to properly fix the hugetlb
put_page path (free_huge_page).  This RFC provides a possible way to
address the issue.  Comments are welcome/encouraged as several attempts
at this have been made in the past.

This series is based on v5.12-rc3.  At a high level, this series does:
- Patches 1 & 2 are cleanups/fixes to existing code in the areas to be
  modified.
- Patches 3, 4 & 5 are aimed at reducing lock hold times.  To be clear
  the goal is to eliminate single lock hold times of a long duration.
  Overall lock hold time is not addressed.  In addition, the known
  long hold time in hugetlb_cgroup_css_offline still needs to be
  addressed (suggestions welcome).
- Patch 6 makes hugetlb_lock and subpool lock IRQ safe.  It also reverts
  the code which defers calls to a workqueue if !in_task.
- Patch 7 adds code to defer freeing of pages to a workqueue if the freeing
  routines could possibly sleep.
- Patch 8 adds a flag to gigantic pages allocated from CMA so that we
  only defer freeing those pages.

[1] https://lore.kernel.org/linux-mm/000000000000f1c03b05bc43aadc@xxxxxxxxxx/
[2] http://lkml.kernel.org/r/20210311021321.127500-1-mike.kravetz@xxxxxxxxxx

Mike Kravetz (8):
  hugetlb: add per-hstate mutex to synchronize user adjustments
  hugetlb: recompute min_count when dropping hugetlb_lock
  hugetlb: create remove_hugetlb_page() to separate functionality
  hugetlb: call update_and_free_page without hugetlb_lock
  hugetlb: change free_pool_huge_page to remove_pool_huge_page
  hugetlb: make free_huge_page irq safe
  hugetlb: add update_and_free_page_no_sleep for irq context
  hugetlb: track hugetlb pages allocated via cma_alloc

 include/linux/hugetlb.h |  20 +-
 mm/hugetlb.c            | 450 +++++++++++++++++++++++++---------------
 mm/hugetlb_cgroup.c     |  10 +-
 3 files changed, 310 insertions(+), 170 deletions(-)

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2.30.2