[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>

diff --git a/drivers/s390/scsi/zfcp_aux.c b/drivers/s390/scsi/zfcp_aux.c
index 351d2e711ec5a28af45178007f9c2283c5fdd091..5dcac24a7a1bf24b8fb193e7406a1dc5df7c789e 100644 (file)
--- 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 95644b71836e8ee187a11cebe9467c760ecc0a8a..9fe32f7ec8d2f732f554c7df3fb3c6b68dba7697 100644 (file)
--- 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) {