[PATCH] libata: Prevent the interrupt handler from completing a command twice

Problem:
During the libata CD-ROM stress test, sometimes the "BUG: timeout
without command" error is seen.

Root cause:
Unexpected interrupt occurs after the ata_qc_complete() is called,
but before the SCSI error handler. The interrupt handler is invoked
before the SCSI error handler, and it clears the command by calling
ata_qc_complete() again. Later when the SCSI error handler is run,
the ata_queued_cmd is already gone, causing the "BUG: timeout without
command" error.

Changes:
- Use the ATA_QCFLAG_ACTIVE flag to prevent the interrupt handler
from completing the command twice, before the scsi_error_handler.

Signed-off-by: Albert Lee <[e-mail]>

drivers/scsi/libata-core.c

···
 	ata_sg_init_one(qc, cmd->sense_buffer, sizeof(cmd->sense_buffer));
 	qc->dma_dir = DMA_FROM_DEVICE;
 
-	memset(&qc->cdb, 0, sizeof(ap->cdb_len));
+	memset(&qc->cdb, 0, ap->cdb_len);
 	qc->cdb[0] = REQUEST_SENSE;
 	qc->cdb[4] = SCSI_SENSE_BUFFERSIZE;
 
···
 
 	/* call completion callback */
 	rc = qc->complete_fn(qc, drv_stat);
+	qc->flags &= ~ATA_QCFLAG_ACTIVE;
 
 	/* if callback indicates not to complete command (non-zero),
 	 * return immediately
···
 			struct ata_queued_cmd *qc;
 
 			qc = ata_qc_from_tag(ap, ap->active_tag);
-			if (qc && (!(qc->tf.ctl & ATA_NIEN)))
+			if (qc && (!(qc->tf.ctl & ATA_NIEN)) &&
+			    (qc->flags & ATA_QCFLAG_ACTIVE))
 				handled |= ata_host_intr(ap, qc);
 		}
 	}