[PATCH 10/11] fs: fix hungtask due to repeated traversal of inodes list

[Ye Bin]

From: Ye Bin <yebin10 at huawei.com>

There's a issue when remove scsi disk, the invalidate_inodes() function
cannot exit for a long time, then trigger hungtask:
INFO: task kworker/56:0:1391396 blocked for more than 122 seconds.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
Workqueue: events_freezable virtscsi_handle_event [virtio_scsi]
Call Trace:
 __schedule+0x33c/0x7f0
 schedule+0x46/0xb0
 schedule_preempt_disabled+0xa/0x10
 __mutex_lock.constprop.0+0x22b/0x490
 mutex_lock+0x52/0x70
 scsi_scan_target+0x6d/0xf0
 virtscsi_handle_event+0x152/0x1a0 [virtio_scsi]
 process_one_work+0x1b2/0x350
 worker_thread+0x49/0x310
 kthread+0xfb/0x140
 ret_from_fork+0x1f/0x30

PID: 540499  TASK: ffff9b15e504c080  CPU: 44  COMMAND: "kworker/44:0"
Call trace:
 invalidate_inodes at ffffffff8f3b4784
 __invalidate_device at ffffffff8f3dfea3
 invalidate_partition at ffffffff8f526b49
 del_gendisk at ffffffff8f5280fb
 sd_remove at ffffffffc0186455 [sd_mod]
 __device_release_driver at ffffffff8f738ab2
 device_release_driver at ffffffff8f738bc4
 bus_remove_device at ffffffff8f737f66
 device_del at ffffffff8f73341b
 __scsi_remove_device at ffffffff8f780340
 scsi_remove_device at ffffffff8f7803a2
 virtscsi_handle_event at ffffffffc017204f [virtio_scsi]
 process_one_work at ffffffff8f1041f2
 worker_thread at ffffffff8f104789
 kthread at ffffffff8f109abb
 ret_from_fork at ffffffff8f001d6f

As commit 04646aebd30b ("fs: avoid softlockups in s_inodes iterators")
introduces the retry logic. In the problem environment, the 'i_count'
of millions of files is not zero. As a result, the time slice for each
traversal to the matching inode process is almost used up, and then the
traversal is started from scratch. The worst-case scenario is that only
one inode can be processed after each wakeup. Because this process holds
a lock, other processes will be stuck for a long time, causing a series
of problems.
To solve the problem of repeated traversal from the beginning, each time
the CPU needs to be freed, a cursor is inserted into the linked list, and
the traversal continues from the cursor next time.

Fixes: 04646aebd30b ("fs: avoid softlockups in s_inodes iterators")
Signed-off-by: Ye Bin <yebin10 at huawei.com>
---
 fs/inode.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index dc966990bda6..b78895af8779 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -857,11 +857,16 @@ static void dispose_list(struct list_head *head)
 void evict_inodes(struct super_block *sb)
 {
 	struct inode *inode, *next;
+	struct inode cursor;
 	LIST_HEAD(dispose);
 
+	cursor.i_state = I_CURSOR;
+	INIT_LIST_HEAD(&cursor.i_sb_list);
+	inode = list_entry(&sb->s_inodes, typeof(*inode), i_sb_list);
+
 again:
 	spin_lock(&sb->s_inode_list_lock);
-	sb_for_each_inodes_safe(inode, next, &sb->s_inodes) {
+	sb_for_each_inodes_continue_safe(inode, next, &sb->s_inodes) {
 		if (atomic_read(&inode->i_count))
 			continue;
 
@@ -886,12 +891,16 @@ void evict_inodes(struct super_block *sb)
 		 * bit so we don't livelock.
 		 */
 		if (need_resched()) {
+			list_del(&cursor.i_sb_list);
+			list_add(&cursor.i_sb_list, &inode->i_sb_list);
+			inode = &cursor;
 			spin_unlock(&sb->s_inode_list_lock);
 			cond_resched();
 			dispose_list(&dispose);
 			goto again;
 		}
 	}
+	list_del(&cursor.i_sb_list);
 	spin_unlock(&sb->s_inode_list_lock);
 
 	dispose_list(&dispose);
@@ -907,11 +916,16 @@ EXPORT_SYMBOL_GPL(evict_inodes);
 void invalidate_inodes(struct super_block *sb)
 {
 	struct inode *inode, *next;
+	struct inode cursor;
 	LIST_HEAD(dispose);
 
+	cursor.i_state = I_CURSOR;
+	INIT_LIST_HEAD(&cursor.i_sb_list);
+	inode = list_entry(&sb->s_inodes, typeof(*inode), i_sb_list);
+
 again:
 	spin_lock(&sb->s_inode_list_lock);
-	sb_for_each_inodes_safe(inode, next, &sb->s_inodes) {
+	sb_for_each_inodes_continue_safe(inode, next, &sb->s_inodes) {
 		spin_lock(&inode->i_lock);
 		if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
 			spin_unlock(&inode->i_lock);
@@ -927,12 +941,16 @@ void invalidate_inodes(struct super_block *sb)
 		spin_unlock(&inode->i_lock);
 		list_add(&inode->i_lru, &dispose);
 		if (need_resched()) {
+			list_del(&cursor.i_sb_list);
+			list_add(&cursor.i_sb_list, &inode->i_sb_list);
+			inode = &cursor;
 			spin_unlock(&sb->s_inode_list_lock);
 			cond_resched();
 			dispose_list(&dispose);
 			goto again;
 		}
 	}
+	list_del(&cursor.i_sb_list);
 	spin_unlock(&sb->s_inode_list_lock);
 
 	dispose_list(&dispose);
-- 
2.34.1