Message ID | 20200117181200.20299-1-cai@lca.pw (mailing list archive) |
---|---|
State | New, archived |
Headers | show |
Series | [-next,v6] mm/hotplug: silence a lockdep splat with printk() | expand |
On Fri 17-01-20 13:12:00, Qian Cai wrote: > It is not that hard to trigger lockdep splats by calling printk from > under zone->lock. Most of them are false positives caused by lock chains > introduced early in the boot process and they do not cause any real > problems (although most of the early boot lock dependencies could > happen after boot as well). There are some console drivers which do > allocate from the printk context as well and those should be fixed. In > any case, false positives are not that trivial to workaround and it is > far from optimal to lose lockdep functionality for something that is a > non-issue. > > 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. > > Even though has_unmovable_pages doesn't hold any reference to the > returned page this should be reasonably safe for the purpose of > reporting the page (dump_page) because it cannot be hotremoved in the > context of memory unplug. The state of the page might change but that is > the case even with the existing code as zone->lock only plays role for > free pages. > > While at it, remove a similar but unnecessary debug-only printk() as > well. A sample of one of those lockdep splats is, > > WARNING: possible circular locking dependency detected > ------------------------------------------------------ > test.sh/8653 is trying to acquire lock: > ffffffff865a4460 (console_owner){-.-.}, at: > console_unlock+0x207/0x750 > > but task is already holding lock: > ffff88883fff3c58 (&(&zone->lock)->rlock){-.-.}, at: > __offline_isolated_pages+0x179/0x3e0 > > which lock already depends on the new lock. > > the existing dependency chain (in reverse order) is: > > -> #3 (&(&zone->lock)->rlock){-.-.}: > __lock_acquire+0x5b3/0xb40 > lock_acquire+0x126/0x280 > _raw_spin_lock+0x2f/0x40 > rmqueue_bulk.constprop.21+0xb6/0x1160 > get_page_from_freelist+0x898/0x22c0 > __alloc_pages_nodemask+0x2f3/0x1cd0 > alloc_pages_current+0x9c/0x110 > allocate_slab+0x4c6/0x19c0 > new_slab+0x46/0x70 > ___slab_alloc+0x58b/0x960 > __slab_alloc+0x43/0x70 > __kmalloc+0x3ad/0x4b0 > __tty_buffer_request_room+0x100/0x250 > tty_insert_flip_string_fixed_flag+0x67/0x110 > pty_write+0xa2/0xf0 > n_tty_write+0x36b/0x7b0 > tty_write+0x284/0x4c0 > __vfs_write+0x50/0xa0 > vfs_write+0x105/0x290 > redirected_tty_write+0x6a/0xc0 > do_iter_write+0x248/0x2a0 > vfs_writev+0x106/0x1e0 > do_writev+0xd4/0x180 > __x64_sys_writev+0x45/0x50 > do_syscall_64+0xcc/0x76c > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > -> #2 (&(&port->lock)->rlock){-.-.}: > __lock_acquire+0x5b3/0xb40 > lock_acquire+0x126/0x280 > _raw_spin_lock_irqsave+0x3a/0x50 > tty_port_tty_get+0x20/0x60 > tty_port_default_wakeup+0xf/0x30 > tty_port_tty_wakeup+0x39/0x40 > uart_write_wakeup+0x2a/0x40 > serial8250_tx_chars+0x22e/0x440 > serial8250_handle_irq.part.8+0x14a/0x170 > serial8250_default_handle_irq+0x5c/0x90 > serial8250_interrupt+0xa6/0x130 > __handle_irq_event_percpu+0x78/0x4f0 > handle_irq_event_percpu+0x70/0x100 > handle_irq_event+0x5a/0x8b > handle_edge_irq+0x117/0x370 > do_IRQ+0x9e/0x1e0 > ret_from_intr+0x0/0x2a > cpuidle_enter_state+0x156/0x8e0 > cpuidle_enter+0x41/0x70 > call_cpuidle+0x5e/0x90 > do_idle+0x333/0x370 > cpu_startup_entry+0x1d/0x1f > start_secondary+0x290/0x330 > secondary_startup_64+0xb6/0xc0 > > -> #1 (&port_lock_key){-.-.}: > __lock_acquire+0x5b3/0xb40 > lock_acquire+0x126/0x280 > _raw_spin_lock_irqsave+0x3a/0x50 > serial8250_console_write+0x3e4/0x450 > univ8250_console_write+0x4b/0x60 > console_unlock+0x501/0x750 > vprintk_emit+0x10d/0x340 > vprintk_default+0x1f/0x30 > vprintk_func+0x44/0xd4 > printk+0x9f/0xc5 > > -> #0 (console_owner){-.-.}: > check_prev_add+0x107/0xea0 > validate_chain+0x8fc/0x1200 > __lock_acquire+0x5b3/0xb40 > lock_acquire+0x126/0x280 > console_unlock+0x269/0x750 > vprintk_emit+0x10d/0x340 > vprintk_default+0x1f/0x30 > vprintk_func+0x44/0xd4 > printk+0x9f/0xc5 > __offline_isolated_pages.cold.52+0x2f/0x30a > offline_isolated_pages_cb+0x17/0x30 > walk_system_ram_range+0xda/0x160 > __offline_pages+0x79c/0xa10 > offline_pages+0x11/0x20 > memory_subsys_offline+0x7e/0xc0 > device_offline+0xd5/0x110 > state_store+0xc6/0xe0 > dev_attr_store+0x3f/0x60 > sysfs_kf_write+0x89/0xb0 > kernfs_fop_write+0x188/0x240 > __vfs_write+0x50/0xa0 > vfs_write+0x105/0x290 > ksys_write+0xc6/0x160 > __x64_sys_write+0x43/0x50 > do_syscall_64+0xcc/0x76c > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > other info that might help us debug this: > > Chain exists of: > console_owner --> &(&port->lock)->rlock --> &(&zone->lock)->rlock > > Possible unsafe locking scenario: > > CPU0 CPU1 > ---- ---- > lock(&(&zone->lock)->rlock); > lock(&(&port->lock)->rlock); > lock(&(&zone->lock)->rlock); > lock(console_owner); > > *** DEADLOCK *** > > 9 locks held by test.sh/8653: > #0: ffff88839ba7d408 (sb_writers#4){.+.+}, at: > vfs_write+0x25f/0x290 > #1: ffff888277618880 (&of->mutex){+.+.}, at: > kernfs_fop_write+0x128/0x240 > #2: ffff8898131fc218 (kn->count#115){.+.+}, at: > kernfs_fop_write+0x138/0x240 > #3: ffffffff86962a80 (device_hotplug_lock){+.+.}, at: > lock_device_hotplug_sysfs+0x16/0x50 > #4: ffff8884374f4990 (&dev->mutex){....}, at: > device_offline+0x70/0x110 > #5: ffffffff86515250 (cpu_hotplug_lock.rw_sem){++++}, at: > __offline_pages+0xbf/0xa10 > #6: ffffffff867405f0 (mem_hotplug_lock.rw_sem){++++}, at: > percpu_down_write+0x87/0x2f0 > #7: ffff88883fff3c58 (&(&zone->lock)->rlock){-.-.}, at: > __offline_isolated_pages+0x179/0x3e0 > #8: ffffffff865a4920 (console_lock){+.+.}, at: > vprintk_emit+0x100/0x340 > > stack backtrace: > Hardware name: HPE ProLiant DL560 Gen10/ProLiant DL560 Gen10, > BIOS U34 05/21/2019 > Call Trace: > dump_stack+0x86/0xca > print_circular_bug.cold.31+0x243/0x26e > check_noncircular+0x29e/0x2e0 > check_prev_add+0x107/0xea0 > validate_chain+0x8fc/0x1200 > __lock_acquire+0x5b3/0xb40 > lock_acquire+0x126/0x280 > console_unlock+0x269/0x750 > vprintk_emit+0x10d/0x340 > vprintk_default+0x1f/0x30 > vprintk_func+0x44/0xd4 > printk+0x9f/0xc5 > __offline_isolated_pages.cold.52+0x2f/0x30a > offline_isolated_pages_cb+0x17/0x30 > walk_system_ram_range+0xda/0x160 > __offline_pages+0x79c/0xa10 > offline_pages+0x11/0x20 > memory_subsys_offline+0x7e/0xc0 > device_offline+0xd5/0x110 > state_store+0xc6/0xe0 > dev_attr_store+0x3f/0x60 > sysfs_kf_write+0x89/0xb0 > kernfs_fop_write+0x188/0x240 > __vfs_write+0x50/0xa0 > vfs_write+0x105/0x290 > ksys_write+0xc6/0x160 > __x64_sys_write+0x43/0x50 > do_syscall_64+0xcc/0x76c > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > Reviewed-by: David Hildenbrand <david@redhat.com> > Signed-off-by: Qian Cai <cai@lca.pw> Acked-by: Michal Hocko <mhocko@suse.com>
diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h index 148e65a9c606..572458016331 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..a90da5337c14 100644 --- a/mm/debug.c +++ b/mm/debug.c @@ -46,6 +46,13 @@ void __dump_page(struct page *page, const char *reason) { struct address_space *mapping; bool page_poisoned = PagePoisoned(page); + /* + * Accessing the pageblock without the zone lock. It could change to + * "isolate" again in the meantime, but since we are just dumping the + * state for debugging, it should be fine to accept a bit of + * inaccuracy here due to racing. + */ + bool page_cma = is_migrate_cma_page(page); int mapcount; char *type = ""; @@ -92,7 +99,8 @@ 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\n", type, page->flags, &page->flags, + page_cma ? " CMA" : ""); hex_only: print_hex_dump(KERN_WARNING, "raw: ", DUMP_PREFIX_NONE, 32, diff --git a/mm/page_alloc.c b/mm/page_alloc.c index e56cd1f33242..621716a25639 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -8202,13 +8202,17 @@ 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. + * + * Returns a page without holding a reference. If the caller wants to + * dereference that page (e.g., dumping), it has to make sure that that it + * cannot get removed (e.g., via memory unplug) concurrently. + * */ -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 +8229,8 @@ 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 +8305,10 @@ 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 +8712,6 @@ __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..e70586523ca3 100644 --- a/mm/page_isolation.c +++ b/mm/page_isolation.c @@ -17,6 +17,7 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_flags) { + struct page *unmovable = NULL; struct zone *zone; unsigned long flags; int ret = -EBUSY; @@ -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; }