scsi: core: Remove the /proc/scsi/${proc_name} directory earlier

Remove the /proc/scsi/${proc_name} directory earlier to fix a race
condition between unloading and reloading kernel modules. This fixes a bug
introduced in 2009 by commit 77c0197 ("[SCSI] fix /proc memory leak in
the SCSI core").

Fix the following kernel warning:

proc_dir_entry 'scsi/scsi_debug' already registered
WARNING: CPU: 19 PID: 27986 at fs/proc/generic.c:376 proc_register+0x27d/0x2e0
Call Trace:
 proc_mkdir+0xb5/0xe0
 scsi_proc_hostdir_add+0xb5/0x170
 scsi_host_alloc+0x683/0x6c0
 sdebug_driver_probe+0x6b/0x2d0 [scsi_debug]
 really_probe+0x159/0x540
 __driver_probe_device+0xdc/0x230
 driver_probe_device+0x4f/0x120
 __device_attach_driver+0xef/0x180
 bus_for_each_drv+0xe5/0x130
 __device_attach+0x127/0x290
 device_initial_probe+0x17/0x20
 bus_probe_device+0x110/0x130
 device_add+0x673/0xc80
 device_register+0x1e/0x30
 sdebug_add_host_helper+0x1a7/0x3b0 [scsi_debug]
 scsi_debug_init+0x64f/0x1000 [scsi_debug]
 do_one_initcall+0xd7/0x470
 do_init_module+0xe7/0x330
 load_module+0x122a/0x12c0
 __do_sys_finit_module+0x124/0x1a0
 __x64_sys_finit_module+0x46/0x50
 do_syscall_64+0x38/0x80
 entry_SYSCALL_64_after_hwframe+0x46/0xb0

Link: https://lore.kernel.org/r/20230210205200.36973-3-bvanassche@acm.org
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Yi Zhang <yi.zhang@redhat.com>
Cc: stable@vger.kernel.org
Fixes: 77c0197 ("[SCSI] fix /proc memory leak in the SCSI core")
Reported-by: Yi Zhang <yi.zhang@redhat.com>
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/hosts.c

@@ -181,6 +181,7 @@ void scsi_remove_host(struct Scsi_Host *shost)
 	scsi_forget_host(shost);
 	mutex_unlock(&shost->scan_mutex);
 	scsi_proc_host_rm(shost);
+	scsi_proc_hostdir_rm(shost->hostt);
 
 	/*
 	 * New SCSI devices cannot be attached anymore because of the SCSI host
@@ -340,6 +341,7 @@ static void scsi_host_dev_release(struct device *dev)
 	struct Scsi_Host *shost = dev_to_shost(dev);
 	struct device *parent = dev->parent;
 
+	/* In case scsi_remove_host() has not been called. */
 	scsi_proc_hostdir_rm(shost->hostt);
 
 	/* Wait for functions invoked through call_rcu(&scmd->rcu, ...) */