From: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Subject: mm/cma: change cma mutex to irq safe spinlock Patch series "make hugetlb put_page safe for all calling contexts", v5. 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 patch (of 8): cma_release is currently a sleepable operatation because the bitmap manipulation is protected by cma->lock mutex. Hugetlb code which relies on cma_release for CMA backed (giga) hugetlb pages, however, needs to be irq safe. The lock doesn't protect any sleepable operation so it can be changed to a (irq aware) spin lock. The bitmap processing should be quite fast in typical case but if cma sizes grow to TB then we will likely need to replace the lock by a more optimized bitmap implementation. Link: https://lkml.kernel.org/r/20210409205254.242291-1-mike.kravetz@xxxxxxxxxx Link: https://lkml.kernel.org/r/20210409205254.242291-2-mike.kravetz@xxxxxxxxxx Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> Acked-by: Roman Gushchin <guro@xxxxxx> Cc: Shakeel Butt <shakeelb@xxxxxxxxxx> Cc: Oscar Salvador <osalvador@xxxxxxx> Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx> Cc: David Rientjes <rientjes@xxxxxxxxxx> Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx> Cc: HORIGUCHI NAOYA <naoya.horiguchi@xxxxxxx> Cc: "Aneesh Kumar K . V" <aneesh.kumar@xxxxxxxxxxxxx> Cc: Waiman Long <longman@xxxxxxxxxx> Cc: Peter Xu <peterx@xxxxxxxxxx> Cc: Mina Almasry <almasrymina@xxxxxxxxxx> Cc: Hillf Danton <hdanton@xxxxxxxx> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx> Cc: Barry Song <song.bao.hua@xxxxxxxxxxxxx> Cc: Will Deacon <will@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/cma.c | 18 +++++++++--------- mm/cma.h | 2 +- mm/cma_debug.c | 8 ++++---- 3 files changed, 14 insertions(+), 14 deletions(-) --- a/mm/cma.c~mm-cma-change-cma-mutex-to-irq-safe-spinlock +++ a/mm/cma.c @@ -24,7 +24,6 @@ #include <linux/memblock.h> #include <linux/err.h> #include <linux/mm.h> -#include <linux/mutex.h> #include <linux/sizes.h> #include <linux/slab.h> #include <linux/log2.h> @@ -83,13 +82,14 @@ static void cma_clear_bitmap(struct cma unsigned int count) { unsigned long bitmap_no, bitmap_count; + unsigned long flags; bitmap_no = (pfn - cma->base_pfn) >> cma->order_per_bit; bitmap_count = cma_bitmap_pages_to_bits(cma, count); - mutex_lock(&cma->lock); + spin_lock_irqsave(&cma->lock, flags); bitmap_clear(cma->bitmap, bitmap_no, bitmap_count); - mutex_unlock(&cma->lock); + spin_unlock_irqrestore(&cma->lock, flags); } static void __init cma_activate_area(struct cma *cma) @@ -118,7 +118,7 @@ static void __init cma_activate_area(str pfn += pageblock_nr_pages) init_cma_reserved_pageblock(pfn_to_page(pfn)); - mutex_init(&cma->lock); + spin_lock_init(&cma->lock); #ifdef CONFIG_CMA_DEBUGFS INIT_HLIST_HEAD(&cma->mem_head); @@ -392,7 +392,7 @@ static void cma_debug_show_areas(struct unsigned long nr_part, nr_total = 0; unsigned long nbits = cma_bitmap_maxno(cma); - mutex_lock(&cma->lock); + spin_lock_irq(&cma->lock); pr_info("number of available pages: "); for (;;) { next_zero_bit = find_next_zero_bit(cma->bitmap, nbits, start); @@ -407,7 +407,7 @@ static void cma_debug_show_areas(struct start = next_zero_bit + nr_zero; } pr_cont("=> %lu free of %lu total pages\n", nr_total, cma->count); - mutex_unlock(&cma->lock); + spin_unlock_irq(&cma->lock); } #else static inline void cma_debug_show_areas(struct cma *cma) { } @@ -452,12 +452,12 @@ struct page *cma_alloc(struct cma *cma, return NULL; for (;;) { - mutex_lock(&cma->lock); + spin_lock_irq(&cma->lock); bitmap_no = bitmap_find_next_zero_area_off(cma->bitmap, bitmap_maxno, start, bitmap_count, mask, offset); if (bitmap_no >= bitmap_maxno) { - mutex_unlock(&cma->lock); + spin_unlock_irq(&cma->lock); break; } bitmap_set(cma->bitmap, bitmap_no, bitmap_count); @@ -466,7 +466,7 @@ struct page *cma_alloc(struct cma *cma, * our exclusive use. If the migration fails we will take the * lock again and unmark it. */ - mutex_unlock(&cma->lock); + spin_unlock_irq(&cma->lock); pfn = cma->base_pfn + (bitmap_no << cma->order_per_bit); ret = alloc_contig_range(pfn, pfn + count, MIGRATE_CMA, --- a/mm/cma_debug.c~mm-cma-change-cma-mutex-to-irq-safe-spinlock +++ a/mm/cma_debug.c @@ -36,10 +36,10 @@ static int cma_used_get(void *data, u64 struct cma *cma = data; unsigned long used; - mutex_lock(&cma->lock); + spin_lock_irq(&cma->lock); /* pages counter is smaller than sizeof(int) */ used = bitmap_weight(cma->bitmap, (int)cma_bitmap_maxno(cma)); - mutex_unlock(&cma->lock); + spin_unlock_irq(&cma->lock); *val = (u64)used << cma->order_per_bit; return 0; @@ -53,7 +53,7 @@ static int cma_maxchunk_get(void *data, unsigned long start, end = 0; unsigned long bitmap_maxno = cma_bitmap_maxno(cma); - mutex_lock(&cma->lock); + spin_lock_irq(&cma->lock); for (;;) { start = find_next_zero_bit(cma->bitmap, bitmap_maxno, end); if (start >= bitmap_maxno) @@ -61,7 +61,7 @@ static int cma_maxchunk_get(void *data, end = find_next_bit(cma->bitmap, bitmap_maxno, start); maxchunk = max(end - start, maxchunk); } - mutex_unlock(&cma->lock); + spin_unlock_irq(&cma->lock); *val = (u64)maxchunk << cma->order_per_bit; return 0; --- a/mm/cma.h~mm-cma-change-cma-mutex-to-irq-safe-spinlock +++ a/mm/cma.h @@ -9,7 +9,7 @@ struct cma { unsigned long count; unsigned long *bitmap; unsigned int order_per_bit; /* Order of pages represented by one bit */ - struct mutex lock; + spinlock_t lock; #ifdef CONFIG_CMA_DEBUGFS struct hlist_head mem_head; spinlock_t mem_head_lock; _
