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

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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>
This commit is contained in:
Ming Lei 2020-10-10 11:25:39 +08:00 committed by Martin K. Petersen
parent 3650b228f8
commit 831e3405c2
1 changed files with 4 additions and 3 deletions
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7
drivers/scsi/scsi_scan.c
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@ -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;
}