scst_sysfs: Trigger a lockdep complaint if sysfs work

could trigger a deadlock

This patch causes lockdep to complain if sysfs work could trigger a deadlock.
As an example, for the patch below the following lockdep complaint is generated:

======================================================
[ INFO: possible circular locking dependency detected ]
3.12.0-rc7-dbg+ #5 Tainted: GF          O
-------------------------------------------------------
scst_mgmtd/7527 is trying to acquire lock:
 (scst_tgt_dev){+.+.+.}, at: [<ffffffffa01f9365>] scst_tgt_dev_sysfs_del+0x105/0x1a0 [scst]

but task is already holding lock:
 (&scst_mutex){+.+.+.}, at: [<ffffffffa01eaa46>] scst_free_session+0x56/0x2c0 [scst]

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (&scst_mutex){+.+.+.}:
       [<ffffffff810be983>] lock_acquire+0x93/0x150
       [<ffffffff81619617>] mutex_lock_interruptible_nested+0x77/0x500
       [<ffffffffa01f1f9f>] scst_tgt_dev_process_thread_pid_show+0x5f/0x120 [scst]
       [<ffffffffa01f38d6>] scst_process_sysfs_works+0xe6/0x1d0 [scst]
       [<ffffffffa01f7af0>] sysfs_work_thread_fn+0x120/0x2b0 [scst]
       [<ffffffff8107482a>] kthread+0xea/0xf0
       [<ffffffff81625f6c>] ret_from_fork+0x7c/0xb0

-> #0 (scst_tgt_dev){+.+.+.}:
       [<ffffffff810bdc8a>] __lock_acquire+0x14fa/0x1a60
       [<ffffffff810be983>] lock_acquire+0x93/0x150
       [<ffffffffa01f20df>] scst_kobject_put_and_wait+0x6f/0x140 [scst]
       [<ffffffffa01f9365>] scst_tgt_dev_sysfs_del+0x105/0x1a0 [scst]
       [<ffffffffa01e9114>] scst_free_tgt_dev+0x84/0x210 [scst]
       [<ffffffffa01ea80b>] scst_sess_free_tgt_devs+0x6b/0x100 [scst]
       [<ffffffffa01eaa4e>] scst_free_session+0x5e/0x2c0 [scst]
       [<ffffffffa01ead4e>] scst_free_session_callback+0x9e/0x170 [scst]
       [<ffffffffa01d5a9a>] scst_global_mgmt_thread+0x24a/0x550 [scst]
       [<ffffffff8107482a>] kthread+0xea/0xf0
       [<ffffffff81625f6c>] ret_from_fork+0x7c/0xb0

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&scst_mutex);
                               lock(scst_tgt_dev);
                               lock(&scst_mutex);
  lock(scst_tgt_dev);

 *** DEADLOCK ***

1 lock held by scst_mgmtd/7527:
 #0:  (&scst_mutex){+.+.+.}, at: [<ffffffffa01eaa46>] scst_free_session+0x56/0x2c0 [scst]

stack backtrace:
CPU: 1 PID: 7527 Comm: scst_mgmtd Tainted: GF          O 3.12.0-rc7-dbg+ #5
Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/31/2013
 ffffffff822efd40 ffff88007b7c1ac8 ffffffff8161464a ffffffff822efd40
 ffff88007b7c1b08 ffffffff81610d02 ffff88007b7c1b60 ffff8800692748c0
 0000000000000000 ffff880069274898 ffff880069274120 ffff8800692748c0
Call Trace:
 [<ffffffff8161464a>] dump_stack+0x4e/0x82
 [<ffffffff81610d02>] print_circular_bug+0x201/0x210
 [<ffffffff810bdc8a>] __lock_acquire+0x14fa/0x1a60
 [<ffffffff810be983>] lock_acquire+0x93/0x150
 [<ffffffffa01f9365>] ? scst_tgt_dev_sysfs_del+0x105/0x1a0 [scst]
 [<ffffffffa01f20df>] scst_kobject_put_and_wait+0x6f/0x140 [scst]
 [<ffffffffa01f9365>] ? scst_tgt_dev_sysfs_del+0x105/0x1a0 [scst]
 [<ffffffffa01f9365>] scst_tgt_dev_sysfs_del+0x105/0x1a0 [scst]
 [<ffffffffa01e9114>] scst_free_tgt_dev+0x84/0x210 [scst]
 [<ffffffffa01ea80b>] scst_sess_free_tgt_devs+0x6b/0x100 [scst]
 [<ffffffffa01eaa4e>] scst_free_session+0x5e/0x2c0 [scst]
 [<ffffffffa01ead4e>] scst_free_session_callback+0x9e/0x170 [scst]
 [<ffffffffa01d5a9a>] scst_global_mgmt_thread+0x24a/0x550 [scst]
 [<ffffffff81075850>] ? wake_up_atomic_t+0x30/0x30
 [<ffffffffa01d5850>] ? scst_register_session_non_gpl+0x20/0x20 [scst]
 [<ffffffff8107482a>] kthread+0xea/0xf0
 [<ffffffff81074740>] ? kthread_create_on_node+0x140/0x140
 [<ffffffff81625f6c>] ret_from_fork+0x7c/0xb0
 [<ffffffff81074740>] ? kthread_create_on_node+0x140/0x140



git-svn-id: http://svn.code.sf.net/p/scst/svn/trunk@5095 d57e44dd-8a1f-0410-8b47-8ef2f437770f

scst/include/scst.h

@@ -4211,7 +4211,8 @@ struct sysfs_ops *scst_sysfs_get_sysfs_ops(void);
 #endif
 
 void scst_kobject_put_and_wait(struct kobject *kobj, const char *category,
-			       struct completion *c);
+			       struct completion *c,
+			       struct lockdep_map *dep_map);
 
 /*
  * Returns target driver's root sysfs kobject.
@@ -4481,6 +4482,12 @@ struct scst_sysfs_work_item {
 	int (*sysfs_work_fn)(struct scst_sysfs_work_item *work);
 	struct completion sysfs_work_done;
 	char *buf;
+	/*
+	 * If the caller of scst_sysfs_queue_wait_work() holds a reference on
+	 * a kobject, must point at the lockdep_map structure associated with
+	 * that kobject.
+	 */
+	struct lockdep_map *dep_map;
 
 	union {
 		struct scst_dev_type *devt;
@@ -4519,6 +4526,12 @@ int scst_sysfs_queue_wait_work(struct scst_sysfs_work_item *work);
 void scst_sysfs_work_get(struct scst_sysfs_work_item *work);
 void scst_sysfs_work_put(struct scst_sysfs_work_item *work);
 
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 29)
+#ifdef CONFIG_LOCKDEP
+extern struct lockdep_map scst_dev_dep_map;
+#endif
+#endif
+
 #endif /* CONFIG_SCST_PROC */
 
 char *scst_get_next_lexem(char **token_str);