scsi: qla2xxx: Fix use after free on unload

System crash is observed with stack trace warning of use after
free. There are 2 signals to tell dpc_thread to terminate (UNLOADING
flag and kthread_stop).

On setting the UNLOADING flag when dpc_thread happens to run at the time
and sees the flag, this causes dpc_thread to exit and clean up
itself. When kthread_stop is called for final cleanup, this causes use
after free.

Remove UNLOADING signal to terminate dpc_thread.  Use the kthread_stop
as the main signal to exit dpc_thread.

[596663.812935] kernel BUG at mm/slub.c:294!
[596663.812950] invalid opcode: 0000 [#1] SMP PTI
[596663.812957] CPU: 13 PID: 1475935 Comm: rmmod Kdump: loaded Tainted: G          IOE    --------- -  - 4.18.0-240.el8.x86_64 #1
[596663.812960] Hardware name: HP ProLiant DL380p Gen8, BIOS P70 08/20/2012
[596663.812974] RIP: 0010:__slab_free+0x17d/0x360

...
[596663.813008] Call Trace:
[596663.813022]  ? __dentry_kill+0x121/0x170
[596663.813030]  ? _cond_resched+0x15/0x30
[596663.813034]  ? _cond_resched+0x15/0x30
[596663.813039]  ? wait_for_completion+0x35/0x190
[596663.813048]  ? try_to_wake_up+0x63/0x540
[596663.813055]  free_task+0x5a/0x60
[596663.813061]  kthread_stop+0xf3/0x100
[596663.813103]  qla2x00_remove_one+0x284/0x440 [qla2xxx]

Cc: stable@vger.kernel.org
Signed-off-by: Quinn Tran <qutran@marvell.com>
Signed-off-by: Nilesh Javali <njavali@marvell.com>
Link: https://lore.kernel.org/r/20241115130313.46826-3-njavali@marvell.com
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

Author: Quinn Tran

drivers/scsi/qla2xxx/qla_os.c

@@ -6902,12 +6902,15 @@ qla2x00_do_dpc(void *data)
 	set_user_nice(current, MIN_NICE);
 
 	set_current_state(TASK_INTERRUPTIBLE);
-	while (!kthread_should_stop()) {
+	while (1) {
 		ql_dbg(ql_dbg_dpc, base_vha, 0x4000,
 		    "DPC handler sleeping.\n");
 
 		schedule();
 
+		if (kthread_should_stop())
+			break;
+
 		if (test_and_clear_bit(DO_EEH_RECOVERY, &base_vha->dpc_flags))
 			qla_pci_set_eeh_busy(base_vha);
 
@@ -6920,15 +6923,16 @@ qla2x00_do_dpc(void *data)
 			goto end_loop;
 		}
 
+		if (test_bit(UNLOADING, &base_vha->dpc_flags))
+			/* don't do any work. Wait to be terminated by kthread_stop */
+			goto end_loop;
+
 		ha->dpc_active = 1;
 
 		ql_dbg(ql_dbg_dpc + ql_dbg_verbose, base_vha, 0x4001,
 		    "DPC handler waking up, dpc_flags=0x%lx.\n",
 		    base_vha->dpc_flags);
 
-		if (test_bit(UNLOADING, &base_vha->dpc_flags))
-			break;
-
 		if (IS_P3P_TYPE(ha)) {
 			if (IS_QLA8044(ha)) {
 				if (test_and_clear_bit(ISP_UNRECOVERABLE,
@@ -7241,9 +7245,6 @@ qla2x00_do_dpc(void *data)
 	 */
 	ha->dpc_active = 0;
 
-	/* Cleanup any residual CTX SRBs. */
-	qla2x00_abort_all_cmds(base_vha, DID_NO_CONNECT << 16);
-
 	return 0;
 }