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    Subject[PATCH 3.13.y-ckt 82/85] mmc: core: fix race condition in mmc_wait_data_done
    Date
    3.13.11-ckt28 -stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Jialing Fu <jlfu@marvell.com>

    commit 71f8a4b81d040b3d094424197ca2f1bf811b1245 upstream.

    The following panic is captured in ker3.14, but the issue still exists
    in latest kernel.
    ---------------------------------------------------------------------
    [ 20.738217] c0 3136 (Compiler) Unable to handle kernel NULL pointer dereference
    at virtual address 00000578
    ......
    [ 20.738499] c0 3136 (Compiler) PC is at _raw_spin_lock_irqsave+0x24/0x60
    [ 20.738527] c0 3136 (Compiler) LR is at _raw_spin_lock_irqsave+0x20/0x60
    [ 20.740134] c0 3136 (Compiler) Call trace:
    [ 20.740165] c0 3136 (Compiler) [<ffffffc0008ee900>] _raw_spin_lock_irqsave+0x24/0x60
    [ 20.740200] c0 3136 (Compiler) [<ffffffc0000dd024>] __wake_up+0x1c/0x54
    [ 20.740230] c0 3136 (Compiler) [<ffffffc000639414>] mmc_wait_data_done+0x28/0x34
    [ 20.740262] c0 3136 (Compiler) [<ffffffc0006391a0>] mmc_request_done+0xa4/0x220
    [ 20.740314] c0 3136 (Compiler) [<ffffffc000656894>] sdhci_tasklet_finish+0xac/0x264
    [ 20.740352] c0 3136 (Compiler) [<ffffffc0000a2b58>] tasklet_action+0xa0/0x158
    [ 20.740382] c0 3136 (Compiler) [<ffffffc0000a2078>] __do_softirq+0x10c/0x2e4
    [ 20.740411] c0 3136 (Compiler) [<ffffffc0000a24bc>] irq_exit+0x8c/0xc0
    [ 20.740439] c0 3136 (Compiler) [<ffffffc00008489c>] handle_IRQ+0x48/0xac
    [ 20.740469] c0 3136 (Compiler) [<ffffffc000081428>] gic_handle_irq+0x38/0x7c
    ----------------------------------------------------------------------
    Because in SMP, "mrq" has race condition between below two paths:
    path1: CPU0: <tasklet context>
    static void mmc_wait_data_done(struct mmc_request *mrq)
    {
    mrq->host->context_info.is_done_rcv = true;
    //
    // If CPU0 has just finished "is_done_rcv = true" in path1, and at
    // this moment, IRQ or ICache line missing happens in CPU0.
    // What happens in CPU1 (path2)?
    //
    // If the mmcqd thread in CPU1(path2) hasn't entered to sleep mode:
    // path2 would have chance to break from wait_event_interruptible
    // in mmc_wait_for_data_req_done and continue to run for next
    // mmc_request (mmc_blk_rw_rq_prep).
    //
    // Within mmc_blk_rq_prep, mrq is cleared to 0.
    // If below line still gets host from "mrq" as the result of
    // compiler, the panic happens as we traced.
    wake_up_interruptible(&mrq->host->context_info.wait);
    }

    path2: CPU1: <The mmcqd thread runs mmc_queue_thread>
    static int mmc_wait_for_data_req_done(...
    {
    ...
    while (1) {
    wait_event_interruptible(context_info->wait,
    (context_info->is_done_rcv ||
    context_info->is_new_req));
    static void mmc_blk_rw_rq_prep(...
    {
    ...
    memset(brq, 0, sizeof(struct mmc_blk_request));

    This issue happens very coincidentally; however adding mdelay(1) in
    mmc_wait_data_done as below could duplicate it easily.

    static void mmc_wait_data_done(struct mmc_request *mrq)
    {
    mrq->host->context_info.is_done_rcv = true;
    + mdelay(1);
    wake_up_interruptible(&mrq->host->context_info.wait);
    }

    At runtime, IRQ or ICache line missing may just happen at the same place
    of the mdelay(1).

    This patch gets the mmc_context_info at the beginning of function, it can
    avoid this race condition.

    Signed-off-by: Jialing Fu <jlfu@marvell.com>
    Tested-by: Shawn Lin <shawn.lin@rock-chips.com>
    Fixes: 2220eedfd7ae ("mmc: fix async request mechanism ....")
    Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
    Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    drivers/mmc/core/core.c | 6 ++++--
    1 file changed, 4 insertions(+), 2 deletions(-)

    diff --git a/drivers/mmc/core/core.c b/drivers/mmc/core/core.c
    index 666d8c7..033d03c 100644
    --- a/drivers/mmc/core/core.c
    +++ b/drivers/mmc/core/core.c
    @@ -329,8 +329,10 @@ EXPORT_SYMBOL(mmc_start_bkops);
    */
    static void mmc_wait_data_done(struct mmc_request *mrq)
    {
    - mrq->host->context_info.is_done_rcv = true;
    - wake_up_interruptible(&mrq->host->context_info.wait);
    + struct mmc_context_info *context_info = &mrq->host->context_info;
    +
    + context_info->is_done_rcv = true;
    + wake_up_interruptible(&context_info->wait);
    }

    static void mmc_wait_done(struct mmc_request *mrq)
    --
    1.9.1


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