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Subject[PATCH AUTOSEL 4.19 07/11] scsi: core: Don't start concurrent async scan on same host
Date
From: Ming Lei <ming.lei@redhat.com>

[ Upstream commit 831e3405c2a344018a18fcc2665acc5a38c3a707 ]

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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/scsi/scsi_scan.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index 9a7e3a3bd5ce8..009a5b2aa3d02 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -1722,15 +1722,16 @@ 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);
@@ -1741,7 +1742,6 @@ 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);
@@ -1756,6 +1756,7 @@ 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;
}
--
2.27.0
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