It is guaranteed to trigger a lockdep splat if calling printk() with zone->lock held because there are many places (tty, console drivers, debugobjects etc) would allocate some memory with another lock held which is proved to be difficult to fix them all. A common workaround until the onging effort to make all printk() as deferred happens is to use printk_deferred() in those places similar to the recent commit [1] merged into the random and -next trees, but memory offline will call dump_page() which needs to be deferred after the lock. So change has_unmovable_pages() so that it no longer calls dump_page() itself - instead it returns a "struct page *" of the unmovable page back to the caller so that in the case of a has_unmovable_pages() failure, the caller can call dump_page() after releasing zone->lock. Also, make dump_page() is able to report a CMA page as well, so the reason string from has_unmovable_pages() can be removed. While at it, remove a similar but unnecessary debug-only printk() as well. A few sample lockdep splats can be founnd here [2]. [1] https://lore.kernel.org/lkml/1573679785-21068-1-git-send-email-cai@xxxxxx/ [2] https://lore.kernel.org/lkml/7CD27FC6-CFFF-4519-A57D-85179E9815FE@xxxxxx/ Signed-off-by: Qian Cai <cai@xxxxxx> --- v3: Rebase to next-20200115 for the mm/debug change and update some comments thanks to Michal. v2: Improve the commit log and report CMA in dump_page() per Andrew. has_unmovable_pages() returns a "struct page *" to the caller. include/linux/page-isolation.h | 4 ++-- mm/debug.c | 4 +++- mm/memory_hotplug.c | 6 ++++-- mm/page_alloc.c | 22 +++++++++------------- mm/page_isolation.c | 11 ++++++++++- 5 files changed, 28 insertions(+), 19 deletions(-) diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h index 148e65a9c606..da043ae86488 100644 --- a/include/linux/page-isolation.h +++ b/include/linux/page-isolation.h @@ -33,8 +33,8 @@ static inline bool is_migrate_isolate(int migratetype) #define MEMORY_OFFLINE 0x1 #define REPORT_FAILURE 0x2 -bool has_unmovable_pages(struct zone *zone, struct page *page, int migratetype, - int flags); +struct page *has_unmovable_pages(struct zone *zone, struct page *page, int + migratetype, int flags); void set_pageblock_migratetype(struct page *page, int migratetype); int move_freepages_block(struct zone *zone, struct page *page, int migratetype, int *num_movable); diff --git a/mm/debug.c b/mm/debug.c index 6a52316af839..784f9da711b0 100644 --- a/mm/debug.c +++ b/mm/debug.c @@ -46,6 +46,7 @@ void __dump_page(struct page *page, const char *reason) { struct address_space *mapping; bool page_poisoned = PagePoisoned(page); + bool page_cma = is_migrate_cma_page(page); int mapcount; char *type = ""; @@ -92,7 +93,8 @@ void __dump_page(struct page *page, const char *reason) } BUILD_BUG_ON(ARRAY_SIZE(pageflag_names) != __NR_PAGEFLAGS + 1); - pr_warn("%sflags: %#lx(%pGp)\n", type, page->flags, &page->flags); + pr_warn("%sflags: %#lx(%pGp)%s", type, page->flags, &page->flags, + page_cma ? " CMA\n" : "\n"); hex_only: print_hex_dump(KERN_WARNING, "raw: ", DUMP_PREFIX_NONE, 32, diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 7a6de9b0dcab..06e7dd3eb9a9 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -1148,8 +1148,10 @@ static bool is_pageblock_removable_nolock(unsigned long pfn) if (!zone_spans_pfn(zone, pfn)) return false; - return !has_unmovable_pages(zone, page, MIGRATE_MOVABLE, - MEMORY_OFFLINE); + if (has_unmovable_pages(zone, page, MIGRATE_MOVABLE, MEMORY_OFFLINE)) + return false; + + return true; } /* Checks if this range of memory is likely to be hot-removable. */ diff --git a/mm/page_alloc.c b/mm/page_alloc.c index e56cd1f33242..e90140e879e6 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -8202,13 +8202,16 @@ void *__init alloc_large_system_hash(const char *tablename, * MIGRATE_MOVABLE block might include unmovable pages. And __PageMovable * check without lock_page also may miss some movable non-lru pages at * race condition. So you can't expect this function should be exact. + * + * It returns a page without holding a reference. It should be safe here + * because the page cannot go away because it is unmovable, but it must not to + * be used for anything else rather than dumping its state. */ -bool has_unmovable_pages(struct zone *zone, struct page *page, int migratetype, - int flags) +struct page *has_unmovable_pages(struct zone *zone, struct page *page, + int migratetype, int flags) { unsigned long iter = 0; unsigned long pfn = page_to_pfn(page); - const char *reason = "unmovable page"; /* * TODO we could make this much more efficient by not checking every @@ -8225,9 +8228,8 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int migratetype, * so consider them movable here. */ if (is_migrate_cma(migratetype)) - return false; + return NULL; - reason = "CMA page"; goto unmovable; } @@ -8302,12 +8304,10 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int migratetype, */ goto unmovable; } - return false; + return NULL; unmovable: WARN_ON_ONCE(zone_idx(zone) == ZONE_MOVABLE); - if (flags & REPORT_FAILURE) - dump_page(pfn_to_page(pfn + iter), reason); - return true; + return pfn_to_page(pfn + iter); } #ifdef CONFIG_CONTIG_ALLOC @@ -8711,10 +8711,6 @@ __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn) BUG_ON(!PageBuddy(page)); order = page_order(page); offlined_pages += 1 << order; -#ifdef CONFIG_DEBUG_VM - pr_info("remove from free list %lx %d %lx\n", - pfn, 1 << order, end_pfn); -#endif del_page_from_free_area(page, &zone->free_area[order]); pfn += (1 << order); } diff --git a/mm/page_isolation.c b/mm/page_isolation.c index 1f8b9dfecbe8..f3af65bac1e0 100644 --- a/mm/page_isolation.c +++ b/mm/page_isolation.c @@ -20,6 +20,7 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_ struct zone *zone; unsigned long flags; int ret = -EBUSY; + struct page *unmovable = NULL; zone = page_zone(page); @@ -37,7 +38,8 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_ * FIXME: Now, memory hotplug doesn't call shrink_slab() by itself. * We just check MOVABLE pages. */ - if (!has_unmovable_pages(zone, page, migratetype, isol_flags)) { + unmovable = has_unmovable_pages(zone, page, migratetype, isol_flags); + if (!unmovable) { unsigned long nr_pages; int mt = get_pageblock_migratetype(page); @@ -54,6 +56,13 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_ spin_unlock_irqrestore(&zone->lock, flags); if (!ret) drain_all_pages(zone); + else if (isol_flags & REPORT_FAILURE && unmovable) + /* + * printk() with zone->lock held will guarantee to trigger a + * lockdep splat, so defer it here. + */ + dump_page(unmovable, "unmovable page"); + return ret; } -- 2.21.0 (Apple Git-122.2)
