On Wed, Jul 29, 2015 at 10:22 AM, Jeff Moyer <[email protected]> wrote:
> Hi,
>
> After commit f70ced091707 (blk-mq: support per-distpatch_queue flush
> machinery), the mtip32xx driver may oops upon module load due to walking
> off the end of an array in mtip_init_cmd. On initialization of the
> flush_rq, init_request is called with request_index >= the maximum queue
> depth the driver supports. For mtip32xx, this value is used to index
> into an array. What this means is that the driver will walk off the end
> of the array, and either oops or cause random memory corruption.
>
> The problem is easily reproduced by doing modprobe/rmmod of the mtip32xx
> driver in a loop. I can typically reproduce the problem in about 30
> seconds.
>
> Now, in the case of mtip32xx, it actually doesn't support flush/fua, so
> I think we can simply return without doing anything. In addition, no
> other mq-enabled driver does anything with the request_index passed into
> init_request(), so no other driver is affected. However, I'm not really
> sure what is expected of drivers. Ming, what did you envision drivers
> would do when initializing the flush requests?
Sorry for not checking this driver.
The flush command's index is deliberately set as this value, and it was
documented in include/linux/blk-mq.h:
* Tag greater than or equal to queue_depth is for setting up
* flush request.
Thanks,
>
> Signed-off-by: Jeff Moyer <[email protected]>
>
> diff --git a/drivers/block/mtip32xx/mtip32xx.c
> b/drivers/block/mtip32xx/mtip32xx.c
> index 4a2ef09..f504232 100644
> --- a/drivers/block/mtip32xx/mtip32xx.c
> +++ b/drivers/block/mtip32xx/mtip32xx.c
> @@ -3756,6 +3756,14 @@ static int mtip_init_cmd(void *data, struct request
> *rq, unsigned int hctx_idx,
> struct mtip_cmd *cmd = blk_mq_rq_to_pdu(rq);
> u32 host_cap_64 = readl(dd->mmio + HOST_CAP) & HOST_CAP_64;
>
> + /*
> + * For flush requests, request_idx starts at the end of the
> + * tag space. Since we don't support FLUSH/FUA, simply return
> + * 0 as there's nothing to be done.
> + */
> + if (request_idx >= MTIP_MAX_COMMAND_SLOTS)
> + return 0;
> +
> cmd->command = dmam_alloc_coherent(&dd->pdev->dev, CMD_DMA_ALLOC_SZ,
> &cmd->command_dma, GFP_KERNEL);
> if (!cmd->command)
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