| Message ID | 1384135418-19019-1-git-send-email-b32955@freescale.com |
|---|---|
| State | Accepted |
| Commit | 7b3d2fb92067bcb29f0f085a9fa9fa64920a6646 |
| Headers | show |
diff --git a/drivers/mtd/nand/gpmi-nand/gpmi-nand.c b/drivers/mtd/nand/gpmi-nand/gpmi-nand.c index 7ac2280..f89b4fd 100644 --- a/drivers/mtd/nand/gpmi-nand/gpmi-nand.c +++ b/drivers/mtd/nand/gpmi-nand/gpmi-nand.c @@ -394,8 +394,6 @@ 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); @@ -420,6 +418,8 @@ 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] 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) | stable@vger.kernel.org Signed-off-by: Huang Shijie <b32955@freescale.com> --- fix the wrong diagram. --- drivers/mtd/nand/gpmi-nand/gpmi-nand.c | 4 ++-- 1 files changed, 2 insertions(+), 2 deletions(-)