scsi: sg: reset 'res_in_use' after unlinking reserved array

Once the reserved page array is unused we can reset the 'res_in_use'
state; here we can do a lazy update without holding the mutex as we only
need to check against concurrent access, not concurrent release.

[mkp: checkpatch]

Fixes: 1bc0eb04 ("scsi: sg: protect accesses to 'reserved' page array")
Signed-off-by: NHannes Reinecke <hare@suse.com>
Reviewed-by: NJohannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/sg.c

@@ -2056,6 +2056,8 @@ sg_unlink_reserve(Sg_fd * sfp, Sg_request * srp)
 	req_schp->page_order = 0;
 	req_schp->sglist_len = 0;
 	srp->res_used = 0;
+	/* Called without mutex lock to avoid deadlock */
+	sfp->res_in_use = 0;
 }
 
 static Sg_request *