[PATCH] libata: don't initialize sg in ata_exec_internal() if DMA_NONE (take #2)

Calling sg_init_one() with NULL buf causes oops on certain
configurations.  Don't initialize sg in ata_exec_internal() if
DMA_NONE and make the function complain if @buf is NULL when dma_dir
isn't DMA_NONE.  While at it, fix comment.

The problem is discovered and initial patch was submitted by Arnd
Bergmann.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Cc: Arnd Bergmann <arnd.bergmann@de.ibm.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
index 011c0a8..0d51d13 100644 (file)
--- a/drivers/ata/libata-core.c
+++ b/drivers/ata/libata-core.c
@@ -1332,7 +1332,7 @@ unsigned ata_exec_internal_sg(struct ata_device *dev,
 }
 
 /**
- *     ata_exec_internal_sg - execute libata internal command
+ *     ata_exec_internal - execute libata internal command
  *     @dev: Device to which the command is sent
  *     @tf: Taskfile registers for the command and the result
  *     @cdb: CDB for packet command
@@ -1353,11 +1353,17 @@ unsigned ata_exec_internal(struct ata_device *dev,
                           struct ata_taskfile *tf, const u8 *cdb,
                           int dma_dir, void *buf, unsigned int buflen)
 {
-       struct scatterlist sg;
+       struct scatterlist *psg = NULL, sg;
+       unsigned int n_elem = 0;
 
-       sg_init_one(&sg, buf, buflen);
+       if (dma_dir != DMA_NONE) {
+               WARN_ON(!buf);
+               sg_init_one(&sg, buf, buflen);
+               psg = &sg;
+               n_elem++;
+       }
 
-       return ata_exec_internal_sg(dev, tf, cdb, dma_dir, &sg, 1);
+       return ata_exec_internal_sg(dev, tf, cdb, dma_dir, psg, n_elem);
 }
 
 /**