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    Subject[PATCH AUTOSEL for 4.15 40/78] rtc: ac100: Fix multiple race conditions
    Date
    From: Alexandre Belloni <alexandre.belloni@free-electrons.com>

    [ Upstream commit 994ec64c0a193940be7a6fd074668b9446d3b6c3 ]

    The probe function is not allowed to fail after registering the RTC because
    the following may happen:

    CPU0: CPU1:
    sys_load_module()
    do_init_module()
    do_one_initcall()
    cmos_do_probe()
    rtc_device_register()
    __register_chrdev()
    cdev->owner = struct module*
    open("/dev/rtc0")
    rtc_device_unregister()
    module_put()
    free_module()
    module_free(mod->module_core)
    /* struct module *module is now
    freed */
    chrdev_open()
    spin_lock(cdev_lock)
    cdev_get()
    try_module_get()
    module_is_live()
    /* dereferences already
    freed struct module* */

    Also, the interrupt handler: ac100_rtc_irq() is dereferencing chip->rtc but
    this may still be NULL when it is called, resulting in:
    Unable to handle kernel NULL pointer dereference at virtual address 00000194
    pgd = (ptrval)
    [00000194] *pgd=00000000
    Internal error: Oops: 5 [#1] SMP ARM
    Modules linked in:
    CPU: 0 PID: 72 Comm: irq/71-ac100-rt Not tainted 4.15.0-rc1-next-20171201-dirty #120
    Hardware name: Allwinner sun8i Family
    task: (ptrval) task.stack: (ptrval)
    PC is at mutex_lock+0x14/0x3c
    LR is at ac100_rtc_irq+0x38/0xc8
    pc : [<c06543a4>] lr : [<c04d9a2c>] psr: 60000053
    sp : ee9c9f28 ip : 00000000 fp : ee9adfdc
    r10: 00000000 r9 : c0a04c48 r8 : c015ed18
    r7 : ee9bd600 r6 : ee9c9f28 r5 : ee9af590 r4 : c0a04c48
    r3 : ef3cb3c0 r2 : 00000000 r1 : ee9af590 r0 : 00000194
    Flags: nZCv IRQs on FIQs off Mode SVC_32 ISA ARM Segment none
    Control: 10c5387d Table: 4000406a DAC: 00000051
    Process irq/71-ac100-rt (pid: 72, stack limit = 0x(ptrval))
    Stack: (0xee9c9f28 to 0xee9ca000)
    9f20: 00000000 7c2fd1be c015ed18 ee9adf40 ee9c0400 ee9c0400
    9f40: ee9adf40 c015ed34 ee9c8000 ee9adf64 ee9c0400 c015f040 ee9adf80 00000000
    9f60: c015ee24 7c2fd1be ee9adfc0 ee9adf80 00000000 ee9c8000 ee9adf40 c015eef4
    9f80: ef1eba34 c0138f14 ee9c8000 ee9adf80 c0138df4 00000000 00000000 00000000
    9fa0: 00000000 00000000 00000000 c01010e8 00000000 00000000 00000000 00000000
    9fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
    9fe0: 00000000 00000000 00000000 00000000 00000013 00000000 ffffffff ffffffff
    [<c06543a4>] (mutex_lock) from [<c04d9a2c>] (ac100_rtc_irq+0x38/0xc8)
    [<c04d9a2c>] (ac100_rtc_irq) from [<c015ed34>] (irq_thread_fn+0x1c/0x54)
    [<c015ed34>] (irq_thread_fn) from [<c015f040>] (irq_thread+0x14c/0x214)
    [<c015f040>] (irq_thread) from [<c0138f14>] (kthread+0x120/0x150)
    [<c0138f14>] (kthread) from [<c01010e8>] (ret_from_fork+0x14/0x2c)

    Solve both issues by moving to
    devm_rtc_allocate_device()/rtc_register_device()

    Reported-by: Quentin Schulz <quentin.schulz@free-electrons.com>
    Tested-by: Quentin Schulz <quentin.schulz@free-electrons.com>
    Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    ---
    drivers/rtc/rtc-ac100.c | 19 ++++++++++++-------
    1 file changed, 12 insertions(+), 7 deletions(-)

    diff --git a/drivers/rtc/rtc-ac100.c b/drivers/rtc/rtc-ac100.c
    index 9e336184491c..0e358d4b6738 100644
    --- a/drivers/rtc/rtc-ac100.c
    +++ b/drivers/rtc/rtc-ac100.c
    @@ -567,6 +567,12 @@ static int ac100_rtc_probe(struct platform_device *pdev)
    return chip->irq;
    }

    + chip->rtc = devm_rtc_allocate_device(&pdev->dev);
    + if (IS_ERR(chip->rtc))
    + return PTR_ERR(chip->rtc);
    +
    + chip->rtc->ops = &ac100_rtc_ops;
    +
    ret = devm_request_threaded_irq(&pdev->dev, chip->irq, NULL,
    ac100_rtc_irq,
    IRQF_SHARED | IRQF_ONESHOT,
    @@ -586,17 +592,16 @@ static int ac100_rtc_probe(struct platform_device *pdev)
    /* clear counter alarm pending interrupts */
    regmap_write(chip->regmap, AC100_ALM_INT_STA, AC100_ALM_INT_ENABLE);

    - chip->rtc = devm_rtc_device_register(&pdev->dev, "rtc-ac100",
    - &ac100_rtc_ops, THIS_MODULE);
    - if (IS_ERR(chip->rtc)) {
    - dev_err(&pdev->dev, "unable to register device\n");
    - return PTR_ERR(chip->rtc);
    - }
    -
    ret = ac100_rtc_register_clks(chip);
    if (ret)
    return ret;

    + ret = rtc_register_device(chip->rtc);
    + if (ret) {
    + dev_err(&pdev->dev, "unable to register device\n");
    + return ret;
    + }
    +
    dev_info(&pdev->dev, "RTC enabled\n");

    return 0;
    --
    2.14.1
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