[PATCH] mm: Warn on lock_page() from reclaim context.

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

Kirill A. Shutemov noticed that calling lock_page[_killable]() from
reclaim context might cause deadlock. In order to help finding such
lock_page[_killable]() users (including out of tree users), this patch
emits warning messages when CONFIG_PROVE_LOCKING is enabled.

[   81.532721] ------------[ cut here ]------------
[   81.534253] lock_page() from reclaim context might deadlock
[   81.534264] WARNING: CPU: 3 PID: 56 at mm/filemap.c:3340 __warn_lock_page_from_reclaim_context+0x1e/0x30
[   81.539982] Modules linked in: pcspkr sg vmw_vmci shpchp i2c_piix4 sd_mod ata_generic pata_acpi vmwgfx drm_kms_helper syscopyarea sysfillrect mptspi sysimgblt fb_sys_fops ahci ttm libahci e1000 scsi_transport_spi mptscsih drm ata_piix mptbase i2c_core libata serio_raw ipv6
[   81.546750] CPU: 3 PID: 56 Comm: kswapd0 Kdump: loaded Not tainted 4.16.0-rc5-next-20180316+ #698
[   81.549333] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 05/19/2017
[   81.552256] RIP: 0010:__warn_lock_page_from_reclaim_context+0x1e/0x30
[   81.554164] RSP: 0018:ffffc9000085bbf8 EFLAGS: 00010282
[   81.555833] RAX: 0000000000000000 RBX: ffffea0004b2b880 RCX: 0000000000000007
[   81.558283] RDX: 0000000000000b6d RSI: ffff88013aa0b700 RDI: ffff88013aa0ae80
[   81.562130] RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
[   81.564291] R10: 0000000000000040 R11: 0000000000000000 R12: ffff8801357b4958
[   81.566551] R13: 0000000000000000 R14: ffffffff82068220 R15: 0000000000000002
[   81.568956] FS:  0000000000000000(0000) GS:ffff88013bcc0000(0000) knlGS:0000000000000000
[   81.571310] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   81.573193] CR2: 00000000006020bf CR3: 000000000200f005 CR4: 00000000001606e0
[   81.575453] Call Trace:
[   81.577001]  pagecache_get_page+0x22a/0x230
[   81.578497]  ? iput+0x52/0x2f0
[   81.579762]  shmem_unused_huge_shrink+0x2e9/0x380
[   81.581465]  super_cache_scan+0x17a/0x180
[   81.582999]  shrink_slab+0x218/0x590
[   81.584398]  shrink_node+0x346/0x350
[   81.585777]  kswapd+0x322/0x930
[   81.587090]  kthread+0xf0/0x130
[   81.588370]  ? mem_cgroup_shrink_node+0x320/0x320
[   81.589996]  ? kthread_create_on_node+0x60/0x60
[   81.591670]  ret_from_fork+0x3a/0x50
[   81.593716] Code: f0 41 80 8c 24 08 01 00 00 02 eb b3 90 80 3d b8 54 f8 00 00 74 02 f3 c3 48 c7 c7 b0 87 df 81 c6 05 a6 54 f8 00 01 e8 d2 89 ee ff <0f> 0b c3 0f 1f 44 00 00 66 2e 0f 1f 84 00 00 00 00 00 41 55 41
[   81.599356] ---[ end trace d9238c3d53557ed5 ]---

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Michal Hocko <mhocko@suse.com>
---
 include/linux/pagemap.h | 12 ++++++++++++
 mm/filemap.c            |  8 ++++++++
 2 files changed, 20 insertions(+)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 34ce3ebf..8e38f4a 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -467,6 +467,10 @@ extern int __lock_page_or_retry(struct page *page, struct mm_struct *mm,
 				unsigned int flags);
 extern void unlock_page(struct page *page);
 
+#ifdef CONFIG_PROVE_LOCKING
+extern void __warn_lock_page_from_reclaim_context(void);
+#endif
+
 static inline int trylock_page(struct page *page)
 {
 	page = compound_head(page);
@@ -479,6 +483,10 @@ static inline int trylock_page(struct page *page)
 static inline void lock_page(struct page *page)
 {
 	might_sleep();
+#ifdef CONFIG_PROVE_LOCKING
+	if (unlikely(current->flags & PF_MEMALLOC))
+		__warn_lock_page_from_reclaim_context();
+#endif
 	if (!trylock_page(page))
 		__lock_page(page);
 }
@@ -491,6 +499,10 @@ static inline void lock_page(struct page *page)
 static inline int lock_page_killable(struct page *page)
 {
 	might_sleep();
+#ifdef CONFIG_PROVE_LOCKING
+	if (unlikely(current->flags & PF_MEMALLOC))
+		__warn_lock_page_from_reclaim_context();
+#endif
 	if (!trylock_page(page))
 		return __lock_page_killable(page);
 	return 0;
diff --git a/mm/filemap.c b/mm/filemap.c
index 693f622..de2eb21 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3328,3 +3328,11 @@ int try_to_release_page(struct page *page, gfp_t gfp_mask)
 }
 
 EXPORT_SYMBOL(try_to_release_page);
+
+#ifdef CONFIG_PROVE_LOCKING
+void __warn_lock_page_from_reclaim_context(void)
+{
+	WARN_ONCE(1, "lock_page() from reclaim context might deadlock");
+}
+EXPORT_SYMBOL(__warn_lock_page_from_reclaim_context);
+#endif
-- 
1.8.3.1