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

Mike Kravetz
2021-03-19T22:44:12Z

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@google.com/
[2] http://lkml.kernel.org/r/20210311021321.127500-1-mike.kravetz@oracle.com

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(-)

--
2.30.2