On 12/9/19 9:34 AM, Bart Van Assche wrote:

Some time ago the block layer was modified such that timeout handlers are called from thread context instead of interrupt context. Make it safe to run the iSCSI timeout handler in thread context. This patch fixes the following lockdep complaint:

================================ WARNING: inconsistent lock state 5.5.1-dbg+ #11 Not tainted

---

inconsistent {IN-SOFTIRQ-W} -> {SOFTIRQ-ON-W} usage. kworker/7:1H/206 [HC0[0]:SC0[0]:HE1:SE1] takes: ffff88802d9827e8 (&(&session->frwd_lock)->rlock){+.?.}, at: iscsi_eh_cmd_timed_out+0xa6/0x6d0 [libiscsi] {IN-SOFTIRQ-W} state was registered at: lock_acquire+0x106/0x240 _raw_spin_lock+0x38/0x50 iscsi_check_transport_timeouts+0x3e/0x210 [libiscsi] call_timer_fn+0x132/0x470 __run_timers.part.0+0x39f/0x5b0 run_timer_softirq+0x63/0xc0 __do_softirq+0x12d/0x5fd irq_exit+0xb3/0x110 smp_apic_timer_interrupt+0x131/0x3d0 apic_timer_interrupt+0xf/0x20 default_idle+0x31/0x230 arch_cpu_idle+0x13/0x20 default_idle_call+0x53/0x60 do_idle+0x38a/0x3f0 cpu_startup_entry+0x24/0x30 start_secondary+0x222/0x290 secondary_startup_64+0xa4/0xb0 irq event stamp: 1383705 hardirqs last enabled at (1383705): [<ffffffff81aace5c>] _raw_spin_unlock_irq+0x2c/0x50 hardirqs last disabled at (1383704): [<ffffffff81aacb98>] _raw_spin_lock_irq+0x18/0x50 softirqs last enabled at (1383690): [<ffffffffa0e2efea>] iscsi_queuecommand+0x76a/0xa20 [libiscsi] softirqs last disabled at (1383682): [<ffffffffa0e2e998>] iscsi_queuecommand+0x118/0xa20 [libiscsi]

other info that might help us debug this: Possible unsafe locking scenario:

   CPU0
   ----

lock(&(&session->frwd_lock)->rlock);

<Interrupt> lock(&(&session->frwd_lock)->rlock);

*** DEADLOCK ***

2 locks held by kworker/7:1H/206: #0: ffff8880d57bf928 ((wq_completion)kblockd){+.+.}, at: process_one_work+0x472/0xab0 #1: ffff88802b9c7de8 ((work_completion)(&q->timeout_work)){+.+.}, at: process_one_work+0x476/0xab0

stack backtrace: CPU: 7 PID: 206 Comm: kworker/7:1H Not tainted 5.5.1-dbg+ #11 Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 Workqueue: kblockd blk_mq_timeout_work Call Trace: dump_stack+0xa5/0xe6 print_usage_bug.cold+0x232/0x23b mark_lock+0x8dc/0xa70 __lock_acquire+0xcea/0x2af0 lock_acquire+0x106/0x240 _raw_spin_lock+0x38/0x50 iscsi_eh_cmd_timed_out+0xa6/0x6d0 [libiscsi] scsi_times_out+0xf4/0x440 [scsi_mod] scsi_timeout+0x1d/0x20 [scsi_mod] blk_mq_check_expired+0x365/0x3a0 bt_iter+0xd6/0xf0 blk_mq_queue_tag_busy_iter+0x3de/0x650 blk_mq_timeout_work+0x1af/0x380 process_one_work+0x56d/0xab0 worker_thread+0x7a/0x5d0 kthread+0x1bc/0x210 ret_from_fork+0x24/0x30

Cc: Christoph Hellwig hch@lst.de Cc: Keith Busch keith.busch@intel.com Cc: Lee Duncan lduncan@suse.com Cc: Chris Leech cleech@redhat.com Cc: stable@vger.kernel.org Fixes: 287922eb0b18 ("block: defer timeouts to a workqueue") Signed-off-by: Bart Van Assche bvanassche@acm.org

---

drivers/scsi/libiscsi.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/scsi/libiscsi.c b/drivers/scsi/libiscsi.c index ebd47c0cf9e9..70b99c0e2e67 100644 --- a/drivers/scsi/libiscsi.c +++ b/drivers/scsi/libiscsi.c @@ -1945,7 +1945,7 @@ enum blk_eh_timer_return iscsi_eh_cmd_timed_out(struct scsi_cmnd *sc) ISCSI_DBG_EH(session, "scsi cmd %p timedout\n", sc);

• spin_lock(&session->frwd_lock);

• spin_lock_bh(&session->frwd_lock); task = (struct iscsi_task *)sc->SCp.ptr; if (!task) { /*

@@ -2072,7 +2072,7 @@ enum blk_eh_timer_return iscsi_eh_cmd_timed_out(struct scsi_cmnd *sc) done: if (task) task->last_timeout = jiffies;

• spin_unlock(&session->frwd_lock);

• spin_unlock_bh(&session->frwd_lock); ISCSI_DBG_EH(session, "return %s\n", rc == BLK_EH_RESET_TIMER ? "timer reset" : "shutdown or nh"); return rc;

Reviewed-by: Lee Duncan lduncan@suse.com