From f45a54214a0770582af06bb1e807493d1b7268ab Mon Sep 17 00:00:00 2001
From: Christof Schmitt <christof.schmitt@de.ibm.com>
Date: Thu, 24 Sep 2009 10:23:24 +0200
Subject: [PATCH] [SCSI] zfcp: Fix lockdep warning when offlining device with
offline chpid
=======================================================
[ INFO: possible circular locking dependency detected ]
2.6.31-39.x.20090917-s390xdefault #1
-------------------------------------------------------
kslowcrw/83 is trying to acquire lock:
(&adapter->scan_work){+.+.+.}, at: [<0000000000169c5c>] __cancel_work_timer+0x64/0x3d4
but task is already holding lock:
(&zfcp_data.config_mutex){+.+.+.}, at: [<00000000004671ea>] zfcp_ccw_remove+0x66/0x384
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #1 (&zfcp_data.config_mutex){+.+.+.}:
[<0000000000189962>] __lock_acquire+0xe26/0x1834
[<000000000018a4b6>] lock_acquire+0x146/0x178
[<000000000058cb5a>] mutex_lock_nested+0x82/0x3ec
[<0000000000477170>] zfcp_fc_scan_ports+0x3ec/0x728
[<0000000000168e34>] worker_thread+0x278/0x3a8
[<000000000016ff08>] kthread+0x9c/0xa4
[<0000000000109ebe>] kernel_thread_starter+0x6/0xc
[<0000000000109eb8>] kernel_thread_starter+0x0/0xc
-> #0 (&adapter->scan_work){+.+.+.}:
[<0000000000189e60>] __lock_acquire+0x1324/0x1834
[<000000000018a4b6>] lock_acquire+0x146/0x178
[<0000000000169c9a>] __cancel_work_timer+0xa2/0x3d4
[<0000000000465cb2>] zfcp_adapter_dequeue+0x32/0x14c
[<00000000004673e4>] zfcp_ccw_remove+0x260/0x384
[<00000000004250f6>] ccw_device_remove+0x42/0x1ac
[<00000000003cb6be>] __device_release_driver+0x9a/0x10c
[<00000000003cb856>] device_release_driver+0x3a/0x4c
[<00000000003ca94c>] bus_remove_device+0xcc/0x114
[<00000000003c8506>] device_del+0x162/0x21c
[<0000000000425ff2>] ccw_device_unregister+0x5e/0x7c
[<000000000042607e>] io_subchannel_remove+0x6e/0x9c
[<000000000041ff9a>] css_remove+0x3e/0x7c
[<00000000003cb6be>] __device_release_driver+0x9a/0x10c
[<00000000003cb856>] device_release_driver+0x3a/0x4c
[<00000000003ca94c>] bus_remove_device+0xcc/0x114
[<00000000003c8506>] device_del+0x162/0x21c
[<00000000003c85e8>] device_unregister+0x28/0x38
[<0000000000420152>] css_sch_device_unregister+0x46/0x58
[<00000000004276a6>] io_subchannel_sch_event+0x28e/0x794
[<0000000000420442>] css_evaluate_known_subchannel+0x46/0xd0
[<0000000000420ebc>] slow_eval_known_fn+0x88/0xa0
[<00000000003caffa>] bus_for_each_dev+0x7e/0xd0
[<000000000042188c>] for_each_subchannel_staged+0x6c/0xd4
[<0000000000421a00>] css_slow_path_func+0x54/0xd8
[<0000000000168e34>] worker_thread+0x278/0x3a8
[<000000000016ff08>] kthread+0x9c/0xa4
[<0000000000109ebe>] kernel_thread_starter+0x6/0xc
[<0000000000109eb8>] kernel_thread_starter+0x0/0xc
cancel_work_sync is called while holding the config_mutex. But the
work that is being cancelled or flushed also uses the config_mutex.
Fix the resulting deadlock possibility by calling cancel_work_sync
earlier without holding the mutex. The best place to do is is after
offlining the device. No new port scan work will be scheduled for the
offline device, so this is a safe place to call cancel_work_sync.
Reviewed-by: Felix Beck <felix.beck@de.ibm.com>
Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>
---
drivers/s390/scsi/zfcp_aux.c | 1 -
drivers/s390/scsi/zfcp_ccw.c | 4 ++++
2 files changed, 4 insertions(+), 1 deletion(-)
diff --git a/drivers/s390/scsi/zfcp_aux.c b/drivers/s390/scsi/zfcp_aux.c
index 351d2e711ec5a..5dcac24a7a1bf 100644
--- a/drivers/s390/scsi/zfcp_aux.c
+++ b/drivers/s390/scsi/zfcp_aux.c
@@ -602,7 +602,6 @@ void zfcp_adapter_dequeue(struct zfcp_adapter *adapter)
int retval = 0;
unsigned long flags;
- cancel_work_sync(&adapter->scan_work);
cancel_work_sync(&adapter->stat_work);
zfcp_fc_wka_ports_force_offline(adapter->gs);
zfcp_adapter_scsi_unregister(adapter);
diff --git a/drivers/s390/scsi/zfcp_ccw.c b/drivers/s390/scsi/zfcp_ccw.c
index 95644b71836e8..9fe32f7ec8d2f 100644
--- a/drivers/s390/scsi/zfcp_ccw.c
+++ b/drivers/s390/scsi/zfcp_ccw.c
@@ -102,7 +102,11 @@ static void zfcp_ccw_remove(struct ccw_device *ccw_device)
adapter = dev_get_drvdata(&ccw_device->dev);
if (!adapter)
goto out;
+ mutex_unlock(&zfcp_data.config_mutex);
+
+ cancel_work_sync(&adapter->scan_work);
+ mutex_lock(&zfcp_data.config_mutex);
write_lock_irq(&zfcp_data.config_lock);
list_for_each_entry_safe(port, p, &adapter->port_list_head, list) {
list_for_each_entry_safe(unit, u, &port->unit_list_head, list) {
--
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