fs/buffer.c: add debug print for __getblk_gfp() stall problem

Among syzbot's unresolved hung task reports, 18 out of 65 reports contain
__getblk_gfp() line in the backtrace.  Since there is a comment block that
says that __getblk_gfp() will lock up the machine if try_to_free_buffers()
attempt from grow_dev_page() is failing, let's start from checking whether
syzbot is hitting that case.  This change will be removed after the bug is
fixed.

Link: http://lkml.kernel.org/r/9b9fcdda-c347-53ee-fdbb-8a7d11cf430e@I-love.SAKURA.ne.jp
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jeff Layton <jlayton@redhat.com>
Cc: <syzkaller-bugs@googlegroups.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>

1 files changed, 48 insertions, 2 deletions

diff --git a/fs/buffer.c b/fs/buffer.c
index b8d28370cfd7..e01f9ac73391 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -996,10 +996,20 @@ grow_dev_page(struct block_device *bdev, sector_t block,
 			end_block = init_page_buffers(page, bdev,
 						(sector_t)index << sizebits,
 						size);
+#ifdef CONFIG_DEBUG_AID_FOR_SYZBOT
+			current->getblk_executed |= 0x01;
+#endif
 			goto done;
 		}
-		if (!try_to_free_buffers(page))
+		if (!try_to_free_buffers(page)) {
+#ifdef CONFIG_DEBUG_AID_FOR_SYZBOT
+			current->getblk_executed |= 0x02;
+#endif
 			goto failed;
+		}
+#ifdef CONFIG_DEBUG_AID_FOR_SYZBOT
+		current->getblk_executed |= 0x04;
+#endif
 	}
 
 	/*
@@ -1019,6 +1029,9 @@ grow_dev_page(struct block_device *bdev, sector_t block,
 	spin_unlock(&inode->i_mapping->private_lock);
 done:
 	ret = (block < end_block) ? 1 : -ENXIO;
+#ifdef CONFIG_DEBUG_AID_FOR_SYZBOT
+	current->getblk_executed |= 0x08;
+#endif
 failed:
 	unlock_page(page);
 	put_page(page);
@@ -1074,6 +1087,12 @@ __getblk_slow(struct block_device *bdev, sector_t block,
 		return NULL;
 	}
 
+#ifdef CONFIG_DEBUG_AID_FOR_SYZBOT
+	current->getblk_stamp = jiffies;
+	current->getblk_executed = 0;
+	current->getblk_bh_count = 0;
+	current->getblk_bh_state = 0;
+#endif
 	for (;;) {
 		struct buffer_head *bh;
 		int ret;
@@ -1085,6 +1104,18 @@ __getblk_slow(struct block_device *bdev, sector_t block,
 		ret = grow_buffers(bdev, block, size, gfp);
 		if (ret < 0)
 			return NULL;
+
+#ifdef CONFIG_DEBUG_AID_FOR_SYZBOT
+		if (!time_after(jiffies, current->getblk_stamp + 3 * HZ))
+			continue;
+		printk(KERN_ERR "%s(%u): getblk(): executed=%x bh_count=%d bh_state=%lx\n",
+		       current->comm, current->pid, current->getblk_executed,
+		       current->getblk_bh_count, current->getblk_bh_state);
+		current->getblk_executed = 0;
+		current->getblk_bh_count = 0;
+		current->getblk_bh_state = 0;
+		current->getblk_stamp = jiffies;
+#endif
 	}
 }
 
@@ -3240,6 +3271,11 @@ EXPORT_SYMBOL(sync_dirty_buffer);
  */
 static inline int buffer_busy(struct buffer_head *bh)
 {
+#ifdef CONFIG_DEBUG_AID_FOR_SYZBOT
+	current->getblk_executed |= 0x80;
+	current->getblk_bh_count = atomic_read(&bh->b_count);
+	current->getblk_bh_state = bh->b_state;
+#endif
 	return atomic_read(&bh->b_count) |
 		(bh->b_state & ((1 << BH_Dirty) | (1 << BH_Lock)));
 }
@@ -3278,11 +3314,18 @@ int try_to_free_buffers(struct page *page)
 	int ret = 0;
 
 	BUG_ON(!PageLocked(page));
-	if (PageWriteback(page))
+	if (PageWriteback(page)) {
+#ifdef CONFIG_DEBUG_AID_FOR_SYZBOT
+		current->getblk_executed |= 0x10;
+#endif
 		return 0;
+	}
 
 	if (mapping == NULL) {		/* can this still happen? */
 		ret = drop_buffers(page, &buffers_to_free);
+#ifdef CONFIG_DEBUG_AID_FOR_SYZBOT
+		current->getblk_executed |= 0x20;
+#endif
 		goto out;
 	}
 
@@ -3306,6 +3349,9 @@ int try_to_free_buffers(struct page *page)
 	if (ret)
 		cancel_dirty_page(page);
 	spin_unlock(&mapping->private_lock);
+#ifdef CONFIG_DEBUG_AID_FOR_SYZBOT
+	current->getblk_executed |= 0x40;
+#endif
 out:
 	if (buffers_to_free) {
 		struct buffer_head *bh = buffers_to_free;