[3.11.y.z extended stable] Patch "mtd: gpmi: fix kernel BUG due to racing DMA operations" has been added to staging queue

Luis Henriques luis.henriques at canonical.com
Thu Dec 5 11:23:05 UTC 2013


This is a note to let you know that I have just added a patch titled

    mtd: gpmi: fix kernel BUG due to racing DMA operations

to the linux-3.11.y-queue branch of the 3.11.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.11.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.11.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From 71e38894f21edd8f5db3a47b93ba84c38fe33572 Mon Sep 17 00:00:00 2001
From: Huang Shijie <b32955 at freescale.com>
Date: Mon, 11 Nov 2013 12:13:45 +0800
Subject: mtd: gpmi: fix kernel BUG due to racing DMA operations

commit 7b3d2fb92067bcb29f0f085a9fa9fa64920a6646 upstream.

[1] The gpmi uses the nand_command_lp to issue the commands to NAND chips.
    The gpmi issues a DMA operation with gpmi_cmd_ctrl when it handles
    a NAND_CMD_NONE control command. So when we read a page(NAND_CMD_READ0)
    from the NAND, we may send two DMA operations back-to-back.

    If we do not serialize the two DMA operations, we will meet a bug when

    1.1) we enable CONFIG_DMA_API_DEBUG, CONFIG_DMADEVICES_DEBUG,
         and CONFIG_DEBUG_SG.

    1.2) Use the following commands in an UART console and a SSH console:
         cmd 1: while true;do dd if=/dev/mtd0 of=/dev/null;done
         cmd 1: while true;do dd if=/dev/mmcblk0 of=/dev/null;done

    The kernel log shows below:
    -----------------------------------------------------------------
    kernel BUG at lib/scatterlist.c:28!
    Unable to handle kernel NULL pointer dereference at virtual address 00000000
      .........................
    [<80044a0c>] (__bug+0x18/0x24) from [<80249b74>] (sg_next+0x48/0x4c)
    [<80249b74>] (sg_next+0x48/0x4c) from [<80255398>] (debug_dma_unmap_sg+0x170/0x1a4)
    [<80255398>] (debug_dma_unmap_sg+0x170/0x1a4) from [<8004af58>] (dma_unmap_sg+0x14/0x6c)
    [<8004af58>] (dma_unmap_sg+0x14/0x6c) from [<8027e594>] (mxs_dma_tasklet+0x18/0x1c)
    [<8027e594>] (mxs_dma_tasklet+0x18/0x1c) from [<8007d444>] (tasklet_action+0x114/0x164)
    -----------------------------------------------------------------

    1.3) Assume the two DMA operations is X (first) and Y (second).

         The root cause of the bug:
	   Assume process P issues DMA X, and sleep on the completion
	 @this->dma_done. X's tasklet callback is dma_irq_callback. It firstly
	 wake up the process sleeping on the completion @this->dma_done,
	 and then trid to unmap the scatterlist S. The waked process P will
	 issue Y in another ARM core. Y initializes S->sg_magic to zero
	 with sg_init_one(), while dma_irq_callback is unmapping S at the same
	 time.

	 See the diagram:

                   ARM core 0              |         ARM core 1
	 -------------------------------------------------------------
         (P issues DMA X, then sleep)  --> |
                                           |
         (X's tasklet wakes P)         --> |
                                           |
                                           | <-- (P begin to issue DMA Y)
                                           |
         (X's tasklet unmap the            |
      scatterlist S with dma_unmap_sg) --> | <-- (Y calls sg_init_one() to init
                                           |      scatterlist S)
                                           |

[2] This patch serialize both the X and Y in the following way:
     Unmap the DMA scatterlist S firstly, and wake up the process at the end
     of the DMA callback, in such a way, Y will be executed after X.

     After this patch:

                   ARM core 0              |         ARM core 1
	 -------------------------------------------------------------
         (P issues DMA X, then sleep)  --> |
                                           |
         (X's tasklet unmap the            |
      scatterlist S with dma_unmap_sg) --> |
                                           |
         (X's tasklet wakes P)         --> |
                                           |
                                           | <-- (P begin to issue DMA Y)
                                           |
                                           | <-- (Y calls sg_init_one() to init
                                           |     scatterlist S)
                                           |

Signed-off-by: Huang Shijie <b32955 at freescale.com>
Signed-off-by: Brian Norris <computersforpeace at gmail.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/mtd/nand/gpmi-nand/gpmi-nand.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/mtd/nand/gpmi-nand/gpmi-nand.c b/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
index 25ecfa1..ab6581f 100644
--- a/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
+++ b/drivers/mtd/nand/gpmi-nand/gpmi-nand.c
@@ -264,8 +264,6 @@ static void dma_irq_callback(void *param)
 	struct gpmi_nand_data *this = param;
 	struct completion *dma_c = &this->dma_done;

-	complete(dma_c);
-
 	switch (this->dma_type) {
 	case DMA_FOR_COMMAND:
 		dma_unmap_sg(this->dev, &this->cmd_sgl, 1, DMA_TO_DEVICE);
@@ -290,6 +288,8 @@ static void dma_irq_callback(void *param)
 	default:
 		pr_err("in wrong DMA operation.\n");
 	}
+
+	complete(dma_c);
 }

 int start_dma_without_bch_irq(struct gpmi_nand_data *this,
--
1.8.3.2





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