[PATCH 4.9 09/41] iscsi-target: Fix iscsi_np reset hung task during parallel delete

Greg Kroah-Hartman
2017-08-15T01:19:25Z

From: Nicholas Bellinger <nab@linux-iscsi.org>

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.

Reported-by: Gary Guo <ghg@datera.io>
Tested-by: Gary Guo <ghg@datera.io>
Cc: Mike Christie <mchristi@redhat.com>
Cc: Hannes Reinecke <hare@suse.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
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(-)

--- a/drivers/target/iscsi/iscsi_target.c
+++ b/drivers/target/iscsi/iscsi_target.c
@@ -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);
--- a/drivers/target/iscsi/iscsi_target_login.c
+++ b/drivers/target/iscsi/iscsi_target_login.c
@@ -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);
--- a/include/target/iscsi/iscsi_target_core.h
+++ b/include/target/iscsi/iscsi_target_core.h
@@ -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;