Patch "iscsi-target: Fix iscsi_np reset hung task during parallel delete" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

iscsi-target: Fix iscsi_np reset hung task during parallel delete

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
iscsi-target-fix-iscsi_np-reset-hung-task-during-parallel-delete.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Nicholas Bellinger <[email protected]>
Date: Fri, 4 Aug 2017 23:59:31 -0700
Subject: iscsi-target: Fix iscsi_np reset hung task during parallel delete

From: Nicholas Bellinger <[email protected]>

commit 978d13d60c34818a41fc35962602bdfa5c03f214 upstream.

This patch fixes a bug associated with iscsit_reset_np_thread() that can occur during parallel configfs rmdir of a single iscsi_np used across multiple iscsi-target instances, that would result in hung task(s) similar to below where configfs rmdir process context was blocked indefinately waiting for iscsi_np->np_restart_comp to finish:

[ 6726.112076] INFO: task dcp_proxy_node_:15550 blocked for more than 120 seconds.
[ 6726.119440]       Tainted: G        W  O     4.1.26-3321 #2
[ 6726.125045] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 6726.132927] dcp_proxy_node_ D ffff8803f202bc88     0 15550      1 0x00000000
[ 6726.140058]  ffff8803f202bc88 ffff88085c64d960 ffff88083b3b1ad0 ffff88087fffeb08
[ 6726.147593]  ffff8803f202c000 7fffffffffffffff ffff88083f459c28 ffff88083b3b1ad0
[ 6726.155132]  ffff88035373c100 ffff8803f202bca8 ffffffff8168ced2 ffff8803f202bcb8
[ 6726.162667] Call Trace:
[ 6726.165150]  [<ffffffff8168ced2>] schedule+0x32/0x80
[ 6726.170156]  [<ffffffff8168f5b4>] schedule_timeout+0x214/0x290
[ 6726.176030]  [<ffffffff810caef2>] ? __send_signal+0x52/0x4a0
[ 6726.181728]  [<ffffffff8168d7d6>] wait_for_completion+0x96/0x100
[ 6726.187774]  [<ffffffff810e7c80>] ? wake_up_state+0x10/0x10
[ 6726.193395]  [<ffffffffa035d6e2>] iscsit_reset_np_thread+0x62/0xe0 [iscsi_target_mod]
[ 6726.201278]  [<ffffffffa0355d86>] iscsit_tpg_disable_portal_group+0x96/0x190 [iscsi_target_mod]
[ 6726.210033]  [<ffffffffa0363f7f>] lio_target_tpg_store_enable+0x4f/0xc0 [iscsi_target_mod]
[ 6726.218351]  [<ffffffff81260c5a>] configfs_write_file+0xaa/0x110
[ 6726.224392]  [<ffffffff811ea364>] vfs_write+0xa4/0x1b0
[ 6726.229576]  [<ffffffff811eb111>] SyS_write+0x41/0xb0
[ 6726.234659]  [<ffffffff8169042e>] system_call_fastpath+0x12/0x71

It would happen because each iscsit_reset_np_thread() sets state to ISCSI_NP_THREAD_RESET, sends SIGINT, and then blocks waiting for completion on iscsi_np->np_restart_comp.

However, if iscsi_np was active processing a login request and more than a single iscsit_reset_np_thread() caller to the same iscsi_np was blocked on iscsi_np->np_restart_comp, iscsi_np kthread process context in __iscsi_target_login_thread() would flush pending signals and only perform a single completion of np->np_restart_comp before going back to sleep within transport specific iscsit_transport->iscsi_accept_np code.

To address this bug, add a iscsi_np->np_reset_count and update __iscsi_target_login_thread() to keep completing np->np_restart_comp until ->np_reset_count has reached zero.

---
 drivers/target/iscsi/iscsi_target.c       |    1 +
 drivers/target/iscsi/iscsi_target_login.c |    7 +++++--
 include/target/iscsi/iscsi_target_core.h  |    1 +
 3 files changed, 7 insertions(+), 2 deletions(-)

@@ -418,6 +418,7 @@ int iscsit_reset_np_thread(
 		return 0;
 	}
 	np->np_thread_state = ISCSI_NP_THREAD_RESET;
+	atomic_inc(&np->np_reset_count);
 
 	if (np->np_thread) {
 		spin_unlock_bh(&np->np_thread_lock);

@@ -1233,9 +1233,11 @@ static int __iscsi_target_login_thread(s
 	flush_signals(current);
 
 	spin_lock_bh(&np->np_thread_lock);
-	if (np->np_thread_state == ISCSI_NP_THREAD_RESET) {
+	if (atomic_dec_if_positive(&np->np_reset_count) >= 0) {
 		np->np_thread_state = ISCSI_NP_THREAD_ACTIVE;
+		spin_unlock_bh(&np->np_thread_lock);
 		complete(&np->np_restart_comp);
+		return 1;
 	} else if (np->np_thread_state == ISCSI_NP_THREAD_SHUTDOWN) {
 		spin_unlock_bh(&np->np_thread_lock);
 		goto exit;

@@ -1268,7 +1270,8 @@ static int __iscsi_target_login_thread(s
 		goto exit;
 	} else if (rc < 0) {
 		spin_lock_bh(&np->np_thread_lock);
-		if (np->np_thread_state == ISCSI_NP_THREAD_RESET) {
+		if (atomic_dec_if_positive(&np->np_reset_count) >= 0) {
+			np->np_thread_state = ISCSI_NP_THREAD_ACTIVE;
 			spin_unlock_bh(&np->np_thread_lock);
 			complete(&np->np_restart_comp);
 			iscsit_put_transport(conn->conn_transport);

@@ -785,6 +785,7 @@ struct iscsi_np {
 	int			np_sock_type;
 	enum np_thread_state_table np_thread_state;
 	bool                    enabled;
+	atomic_t		np_reset_count;
 	enum iscsi_timer_flags_table np_login_timer_flags;
 	u32			np_exports;
 	enum np_flags_table	np_flags;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/target-fix-node_acl-demo-mode-uncached-dynamic-shutdown-regression.patch queue-4.9/iscsi-target-fix-memory-leak-in-iscsit_setup_text_cmd.patch queue-4.9/iscsi-target-fix-iscsi_np-reset-hung-task-during-parallel-delete.patch