Commit 831e3405 authored Oct 10, 2020 by Ming Lei Committed by Martin K. Petersen Oct 26, 2020

scsi: core: Don't start concurrent async scan on same host

The current scanning mechanism is supposed to fall back to a synchronous
host scan if an asynchronous scan is in progress. However, this rule isn't
strictly respected, scsi_prep_async_scan() doesn't hold scan_mutex when
checking shost->async_scan. When scsi_scan_host() is called concurrently,
two async scans on same host can be started and a hang in do_scan_async()
is observed.

Fixes this issue by checking & setting shost->async_scan atomically with
shost->scan_mutex.

Link: https://lore.kernel.org/r/20201010032539.426615-1-ming.lei@redhat.com


Cc: Christoph Hellwig <hch@lst.de>
Cc: Ewan D. Milne <emilne@redhat.com>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Lee Duncan <lduncan@suse.com>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

parent 3650b228

drivers/scsi/scsi_scan.c

+4 −3

Original line number	Diff line number	Diff line
		@@ -1714,15 +1714,16 @@ static void scsi_sysfs_add_devices(struct Scsi_Host *shost)
		*/
		static struct async_scan_data scsi_prep_async_scan(struct Scsi_Host shost)
		{
		struct async_scan_data *data;
		struct async_scan_data *data = NULL;
		unsigned long flags;

		if (strncmp(scsi_scan_type, "sync", 4) == 0)
		return NULL;

		mutex_lock(&shost->scan_mutex);
		if (shost->async_scan) {
		shost_printk(KERN_DEBUG, shost, "%s called twice\n", __func__);
		return NULL;
		goto err;
		}

		data = kmalloc(sizeof(*data), GFP_KERNEL);
		@@ -1733,7 +1734,6 @@ static struct async_scan_data scsi_prep_async_scan(struct Scsi_Host shost)
		goto err;
		init_completion(&data->prev_finished);

		mutex_lock(&shost->scan_mutex);
		spin_lock_irqsave(shost->host_lock, flags);
		shost->async_scan = 1;
		spin_unlock_irqrestore(shost->host_lock, flags);
		@@ -1748,6 +1748,7 @@ static struct async_scan_data scsi_prep_async_scan(struct Scsi_Host shost)
		return data;

		err:
		mutex_unlock(&shost->scan_mutex);
		kfree(data);
		return NULL;
		}

Admin message