======================================================
[ INFO: possible circular locking dependency detected ]
4.10.0-rc7-dbg+ #1 Not tainted
-------------------------------------------------------
rmdir/13321 is trying to acquire lock:
 (&sess->cmdsn_mutex){+.+.+.}, at: [<ffffffffa02cb47d>] iscsit_free_all_ooo_cmdsns+0x2d/0xb0 [iscsi_target_mod]

but task is already holding lock:
 (&sb->s_type->i_mutex_key#14){++++++}, at: [<ffffffff811c6e20>] vfs_rmdir+0x50/0x140

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:
-> #1 (&sb->s_type->i_mutex_key#14){++++++}:
 lock_acquire+0x71/0x90
 down_write+0x3f/0x70
 configfs_depend_item+0x3a/0xb0 [configfs]
 target_depend_item+0x13/0x20 [target_core_mod]
 target_xcopy_locate_se_dev_e4+0xdd/0x1a0 [target_core_mod]
 target_do_xcopy+0x34b/0x970 [target_core_mod]
 __target_execute_cmd+0x22/0xa0 [target_core_mod]
 target_execute_cmd+0x233/0x2c0 [target_core_mod]
 iscsit_execute_cmd+0x208/0x270 [iscsi_target_mod]
 iscsit_sequence_cmd+0x10b/0x190 [iscsi_target_mod]
 iscsit_get_rx_pdu+0x37d/0xcd0 [iscsi_target_mod]
 iscsi_target_rx_thread+0x6e/0xa0 [iscsi_target_mod]
 kthread+0x102/0x140
 ret_from_fork+0x31/0x40

-> #0 (&sess->cmdsn_mutex){+.+.+.}:
 __lock_acquire+0x10e6/0x1260
 lock_acquire+0x71/0x90
 mutex_lock_nested+0x5f/0x670
 iscsit_free_all_ooo_cmdsns+0x2d/0xb0 [iscsi_target_mod]
 iscsit_close_session+0xac/0x200 [iscsi_target_mod]
 lio_tpg_close_session+0x9f/0xb0 [iscsi_target_mod]
 target_shutdown_sessions+0xc3/0xd0 [target_core_mod]
 core_tpg_del_initiator_node_acl+0x91/0x140 [target_core_mod]
 target_fabric_nacl_base_release+0x20/0x30 [target_core_mod]
 config_item_release+0x5a/0xc0 [configfs]
 config_item_put+0x1d/0x1f [configfs]
 configfs_rmdir+0x1a6/0x300 [configfs]
 vfs_rmdir+0xb7/0x140
 do_rmdir+0x1f4/0x200
 SyS_rmdir+0x11/0x20
 entry_SYSCALL_64_fastpath+0x23/0xc6

other info that might help us debug this:

 Possible unsafe locking scenario:
       CPU0                    CPU1
       ----                    ----
  lock(&sb->s_type->i_mutex_key#14);
                               lock(&sess->cmdsn_mutex);
                               lock(&sb->s_type->i_mutex_key#14);
  lock(&sess->cmdsn_mutex);

 *** DEADLOCK ***

3 locks held by rmdir/13321:
 #0:  (sb_writers#10){.+.+.+}, at: [<ffffffff811e1aff>] mnt_want_write+0x1f/0x50
 #1:  (&default_group_class[depth - 1]#2/1){+.+.+.}, at: [<ffffffff811cc8ce>] do_rmdir+0x15e/0x200
 #2:  (&sb->s_type->i_mutex_key#14){++++++}, at: [<ffffffff811c6e20>] vfs_rmdir+0x50/0x140

stack backtrace:
CPU: 2 PID: 13321 Comm: rmdir Not tainted 4.10.0-rc7-dbg+ #1
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.0.0-prebuilt.qemu-project.org 04/01/2014
Call Trace:
 dump_stack+0x86/0xc3
 print_circular_bug+0x1c7/0x220
 __lock_acquire+0x10e6/0x1260
 lock_acquire+0x71/0x90
 mutex_lock_nested+0x5f/0x670
 iscsit_free_all_ooo_cmdsns+0x2d/0xb0 [iscsi_target_mod]
 iscsit_close_session+0xac/0x200 [iscsi_target_mod]
 lio_tpg_close_session+0x9f/0xb0 [iscsi_target_mod]
 target_shutdown_sessions+0xc3/0xd0 [target_core_mod]
 core_tpg_del_initiator_node_acl+0x91/0x140 [target_core_mod]
 target_fabric_nacl_base_release+0x20/0x30 [target_core_mod]
 config_item_release+0x5a/0xc0 [configfs]
 config_item_put+0x1d/0x1f [configfs]
 configfs_rmdir+0x1a6/0x300 [configfs]
 vfs_rmdir+0xb7/0x140
 do_rmdir+0x1f4/0x200
 SyS_rmdir+0x11/0x20
 entry_SYSCALL_64_fastpath+0x23/0xc6

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Andy Grover <agrover@redhat.com>
Cc: David Disseldorp <ddiss@suse.de>
Cc: <stable@vger.kernel.org>
---
 drivers/target/target_core_xcopy.c | 110 +++++++++++++++++++++++--------------
 1 file changed, 69 insertions(+), 41 deletions(-)

diff --git a/drivers/target/target_core_xcopy.c b/drivers/target/target_core_xcopy.c
index cac5a20a4de0..aecb36d955f0 100644
--- a/drivers/target/target_core_xcopy.c
+++ b/drivers/target/target_core_xcopy.c
@@ -40,6 +40,8 @@
 
 static struct workqueue_struct *xcopy_wq = NULL;
 
+static sense_reason_t target_parse_xcopy_cmd(struct xcopy_op *xop);
+
 static int target_xcopy_gen_naa_ieee(struct se_device *dev, unsigned char *buf)
 {
 	int off = 0;
@@ -781,13 +783,24 @@ static int target_xcopy_write_destination(
 static void target_xcopy_do_work(struct work_struct *work)
 {
 	struct xcopy_op *xop = container_of(work, struct xcopy_op, xop_work);
-	struct se_device *src_dev = xop->src_dev, *dst_dev = xop->dst_dev;
 	struct se_cmd *ec_cmd = xop->xop_se_cmd;
-	sector_t src_lba = xop->src_lba, dst_lba = xop->dst_lba, end_lba;
+	struct se_device *src_dev, *dst_dev;
+	sector_t src_lba, dst_lba, end_lba;
 	unsigned int max_sectors;
-	int rc;
-	unsigned short nolb = xop->nolb, cur_nolb, max_nolb, copied_nolb = 0;
+	int rc = 0;
+	unsigned short nolb, cur_nolb, max_nolb, copied_nolb = 0;
+
+	if (target_parse_xcopy_cmd(xop) != TCM_NO_SENSE)
+		goto err_free;
 
+	if (WARN_ON_ONCE(!xop->src_dev) || WARN_ON_ONCE(!xop->dst_dev))
+		goto err_free;
+
+	src_dev = xop->src_dev;
+	dst_dev = xop->dst_dev;
+	src_lba = xop->src_lba;
+	dst_lba = xop->dst_lba;
+	nolb = xop->nolb;
 	end_lba = src_lba + nolb;
 	/*
 	 * Break up XCOPY I/O into hw_max_sectors sized I/O based on the
@@ -855,6 +868,8 @@ static void target_xcopy_do_work(struct work_struct *work)
 
 out:
 	xcopy_pt_undepend_remotedev(xop);
+
+err_free:
 	kfree(xop);
 	/*
 	 * Don't override an error scsi status if it has already been set
@@ -867,48 +882,22 @@ static void target_xcopy_do_work(struct work_struct *work)
 	target_complete_cmd(ec_cmd, ec_cmd->scsi_status);
 }
 
-sense_reason_t target_do_xcopy(struct se_cmd *se_cmd)
+/*
+ * Returns TCM_NO_SENSE upon success or a sense code != TCM_NO_SENSE if parsing
+ * fails.
+ */
+sense_reason_t target_parse_xcopy_cmd(struct xcopy_op *xop)
 {
-	struct se_device *dev = se_cmd->se_dev;
-	struct xcopy_op *xop = NULL;
+	struct se_cmd *se_cmd = xop->xop_se_cmd;
 	unsigned char *p = NULL, *seg_desc;
-	unsigned int list_id, list_id_usage, sdll, inline_dl, sa;
+	unsigned int list_id, list_id_usage, sdll, inline_dl;
 	sense_reason_t ret = TCM_INVALID_PARAMETER_LIST;
 	int rc;
 	unsigned short tdll;
 
-	if (!dev->dev_attrib.emulate_3pc) {
-		pr_err("EXTENDED_COPY operation explicitly disabled\n");
-		return TCM_UNSUPPORTED_SCSI_OPCODE;
-	}
-
-	sa = se_cmd->t_task_cdb[1] & 0x1f;
-	if (sa != 0x00) {
-		pr_err("EXTENDED_COPY(LID4) not supported\n");
-		return TCM_UNSUPPORTED_SCSI_OPCODE;
-	}
-
-	if (se_cmd->data_length == 0) {
-		target_complete_cmd(se_cmd, SAM_STAT_GOOD);
-		return TCM_NO_SENSE;
-	}
-	if (se_cmd->data_length < XCOPY_HDR_LEN) {
-		pr_err("XCOPY parameter truncation: length %u < hdr_len %u\n",
-				se_cmd->data_length, XCOPY_HDR_LEN);
-		return TCM_PARAMETER_LIST_LENGTH_ERROR;
-	}
-
-	xop = kzalloc(sizeof(struct xcopy_op), GFP_KERNEL);
-	if (!xop) {
-		pr_err("Unable to allocate xcopy_op\n");
-		return TCM_OUT_OF_RESOURCES;
-	}
-	xop->xop_se_cmd = se_cmd;
-
 	p = transport_kmap_data_sg(se_cmd);
 	if (!p) {
 		pr_err("transport_kmap_data_sg() failed in target_do_xcopy\n");
-		kfree(xop);
 		return TCM_OUT_OF_RESOURCES;
 	}
 
@@ -977,18 +966,57 @@ sense_reason_t target_do_xcopy(struct se_cmd *se_cmd)
 	pr_debug("XCOPY: Processed %d target descriptors, length: %u\n", rc,
 				rc * XCOPY_TARGET_DESC_LEN);
 	transport_kunmap_data_sg(se_cmd);
-
-	INIT_WORK(&xop->xop_work, target_xcopy_do_work);
-	queue_work(xcopy_wq, &xop->xop_work);
 	return TCM_NO_SENSE;
 
 out:
 	if (p)
 		transport_kunmap_data_sg(se_cmd);
-	kfree(xop);
 	return ret;
 }
 
+sense_reason_t target_do_xcopy(struct se_cmd *se_cmd)
+{
+	struct se_device *dev = se_cmd->se_dev;
+	struct xcopy_op *xop;
+	unsigned int sa;
+
+	if (!dev->dev_attrib.emulate_3pc) {
+		pr_err("EXTENDED_COPY operation explicitly disabled\n");
+		return TCM_UNSUPPORTED_SCSI_OPCODE;
+	}
+
+	sa = se_cmd->t_task_cdb[1] & 0x1f;
+	if (sa != 0x00) {
+		pr_err("EXTENDED_COPY(LID4) not supported\n");
+		return TCM_UNSUPPORTED_SCSI_OPCODE;
+	}
+
+	if (se_cmd->data_length == 0) {
+		target_complete_cmd(se_cmd, SAM_STAT_GOOD);
+		return TCM_NO_SENSE;
+	}
+	if (se_cmd->data_length < XCOPY_HDR_LEN) {
+		pr_err("XCOPY parameter truncation: length %u < hdr_len %u\n",
+				se_cmd->data_length, XCOPY_HDR_LEN);
+		return TCM_PARAMETER_LIST_LENGTH_ERROR;
+	}
+
+	xop = kzalloc(sizeof(struct xcopy_op), GFP_KERNEL);
+	if (!xop)
+		goto err;
+	xop->xop_se_cmd = se_cmd;
+	INIT_WORK(&xop->xop_work, target_xcopy_do_work);
+	if (WARN_ON_ONCE(!queue_work(xcopy_wq, &xop->xop_work)))
+		goto free;
+	return TCM_NO_SENSE;
+
+free:
+	kfree(xop);
+
+err:
+	return TCM_OUT_OF_RESOURCES;
+}
+
 static sense_reason_t target_rcr_operating_parameters(struct se_cmd *se_cmd)
 {
 	unsigned char *p;
