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Subject[PATCH 5.4 59/80] scsi: iscsi: Fix a potential deadlock in the timeout handler
Date
From: Bart Van Assche <bvanassche@acm.org>

commit 5480e299b5ae57956af01d4839c9fc88a465eeab upstream.

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

Fixes: 287922eb0b18 ("block: defer timeouts to a workqueue")
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>
Link: https://lore.kernel.org/r/20191209173457.187370-1-bvanassche@acm.org
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Lee Duncan <lduncan@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/drivers/scsi/libiscsi.c
+++ b/drivers/scsi/libiscsi.c
@@ -1945,7 +1945,7 @@ enum blk_eh_timer_return iscsi_eh_cmd_ti

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_ti
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;

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