This effort is the result a recent bug report [1]. Syzbot found a potential deadlock in the hugetlb put_page/free_huge_page_path. WARNING: SOFTIRQ-safe -> SOFTIRQ-unsafe lock order detected Since the free_huge_page_path already has code to 'hand off' page free requests to a workqueue, a suggestion was proposed to make the in_irq() detection accurate by always enabling PREEMPT_COUNT [2]. The outcome of that discussion was that the hugetlb put_page path (free_huge_page) path should be properly fixed and safe for all calling contexts.
This series is based on v5.12-rc3-mmotm-2021-03-17-22-24. At a high level, the series provides: - Patches 1 & 2 change CMA bitmap mutex to an irq safe spinlock - Patch 3 adds a mutex for proc/sysfs interfaces changing hugetlb counts - Patches 4, 5 & 6 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. - Patch 7 makes hugetlb_lock and subpool lock IRQ safe. It also reverts the code which defers calls to a workqueue if !in_task. - Patch 8 adds some lockdep_assert_held() calls [1] https://lore.kernel.org/linux-mm/000000000000f1c03b05bc43a...@google.com/ [2] http://lkml.kernel.org/r/20210311021321.127500-1-mike.krav...@oracle.com v1 -> v2 - Drop Roman's cma_release_nowait() patches and just change CMA mutex to an IRQ safe spinlock. - Cleanups to variable names, commets and commit messages as suggested by Michal, Oscar, Miaohe and Muchun. - Dropped unnecessary INIT_LIST_HEAD as suggested by Michal and list_del as suggested by Muchun. - Created update_and_free_pages_bulk helper as suggested by Michal. - Rebased on v5.12-rc4-mmotm-2021-03-28-16-37 - Added Acked-by: and Reviewed-by: from v1 RFC -> v1 - Add Roman's cma_release_nowait() patches. This eliminated the need to do a workqueue handoff in hugetlb code. - Use Michal's suggestion to batch pages for freeing. This eliminated the need to recalculate loop control variables when dropping the lock. - Added lockdep_assert_held() calls - Rebased to v5.12-rc3-mmotm-2021-03-17-22-24 Mike Kravetz (8): mm/cma: change cma mutex to irq safe spinlock hugetlb: no need to drop hugetlb_lock to call cma_release hugetlb: add per-hstate mutex to synchronize user adjustments 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 lockdep_assert_held() calls for hugetlb_lock include/linux/hugetlb.h | 1 + mm/cma.c | 20 +-- mm/cma.h | 2 +- mm/cma_debug.c | 10 +- mm/hugetlb.c | 340 +++++++++++++++++++++------------------- mm/hugetlb_cgroup.c | 8 +- 6 files changed, 202 insertions(+), 179 deletions(-) -- 2.30.2
