sg: don't use GFP_ATOMIC in sg_start_req

sg_start_req is called from normal user context and can sleep when
waiting for memory.  Switch it to use GFP_KERNEL, which fixes allocation
failures seend with the bio_alloc rework.

Fixes: b520c4e ("block: split bio_alloc_bioset more clearly into a fast and slowpath")
Reported-by: Shin'ichiro Kawasaki <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>
Tested-by: Shin'ichiro Kawasaki <[email protected]>
Reviewed-by: John Garry <[email protected]>
Reviewed-by: Hannes Reinecke <[email protected]>
Reviewed-by: Bart Van Assche <[email protected]>

Author: Christoph Hellwig

drivers/scsi/sg.c

@@ -1801,7 +1801,7 @@ sg_start_req(Sg_request *srp, unsigned char *cmd)
 	}
 
 	res = blk_rq_map_user_io(rq, md, hp->dxferp, hp->dxfer_len,
-			GFP_ATOMIC, iov_count, iov_count, 1, rw);
+			GFP_KERNEL, iov_count, iov_count, 1, rw);
 	if (!res) {
 		srp->bio = rq->bio;