[PATCH] scsi: memory leak with 1MB tape I/O

[PATCH] scsi: memory leak with 1MB tape I/O

[David Jeffery]

There is a memory leak in the st driver when sending large enough reads or
writes using st's direct I/O path.  As part of mapping the application's
memory, a buffer to hold page pointers is allocated and the count of mapped
pages is stored in field do_dio.  A non-zero do_dio marks that direct I/O is
in use.

But do_dio is only 1 byte in size.  Mapping 256 4k pages overflows
do_dio and causes it to be set to 0, like direct I/O option was not
used.  When the I/O completes, the buffer to hold the page pointers is
not freed, and the page counts of the mapped pages are not reduced.
Every I/O of this size then leaks memory.

The size of do_dio needs to be increased to prevent it wrapping around.

signed-off-by: David Jeffery <djeffery@redhat.com>
---

--- a/drivers/scsi/st.h	2012-04-10 13:21:30.000000000 -0400
+++ b/drivers/scsi/st.h	2012-04-10 14:55:43.000000000 -0400
@@ -35,8 +35,8 @@
 /* The tape buffer descriptor. */
 struct st_buffer {
 	unsigned char dma;	/* DMA-able buffer */
-	unsigned char do_dio;   /* direct i/o set up? */
 	unsigned char cleared;  /* internal buffer cleared after open? */
+	unsigned short do_dio;  /* direct i/o set up? */
 	int buffer_size;
 	int buffer_blocks;
 	int buffer_bytes;

Re: [PATCH] scsi: memory leak with 1MB tape I/O

[Kai Makisara]

[-- Attachment #1: Type: TEXT/PLAIN, Size: 1422 bytes --]

On Wed, 11 Apr 2012, David Jeffery wrote:

> There is a memory leak in the st driver when sending large enough reads or
> writes using st's direct I/O path.  As part of mapping the application's
> memory, a buffer to hold page pointers is allocated and the count of mapped
> pages is stored in field do_dio.  A non-zero do_dio marks that direct I/O is
> in use.
> 
> But do_dio is only 1 byte in size.  Mapping 256 4k pages overflows
> do_dio and causes it to be set to 0, like direct I/O option was not
> used.  When the I/O completes, the buffer to hold the page pointers is
> not freed, and the page counts of the mapped pages are not reduced.
> Every I/O of this size then leaks memory.
> 
> The size of do_dio needs to be increased to prevent it wrapping around.
> 
> signed-off-by: David Jeffery <djeffery@redhat.com>
> ---
> 
> --- a/drivers/scsi/st.h	2012-04-10 13:21:30.000000000 -0400
> +++ b/drivers/scsi/st.h	2012-04-10 14:55:43.000000000 -0400
> @@ -35,8 +35,8 @@
>  /* The tape buffer descriptor. */
>  struct st_buffer {
>  	unsigned char dma;	/* DMA-able buffer */
> -	unsigned char do_dio;   /* direct i/o set up? */
>  	unsigned char cleared;  /* internal buffer cleared after open? */
> +	unsigned short do_dio;  /* direct i/o set up? */
>  	int buffer_size;
>  	int buffer_blocks;
>  	int buffer_bytes;

Acked-by: Kai Mäkisara <kai.makisara@kolumbus.fi>

Thanks,
Kai