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SubjectRe: [PATCH] hid: hid-picolcd: fix possible sleep-in-atomic-context bug
Hi Jia-Ju,

Your checker has been looking at fallback implementation for
the might-sleep hid_alloc_report_buf(GFP_KERNEL).

Did you have a look at the low-lever bus-driver implementations:
hdev->ll_driver->request
^^^^^^^

Are those all sleeping as well or maybe they don't sleep?


I will have a look over the coming days.

Best regards,
Bruno Prémont

On Wed, 18 Dec 2019 16:02:01 +0800 Jia-Ju Bai wrote:
> The driver may sleep while holding a read lock.
> The function call path (from bottom to top) in Linux 4.19 is:
>
> drivers/hid/hid-core.c, 1459:
> hid_alloc_report_buf(GFP_KERNEL) in __hid_request
> ./include/linux/hid.h, 1051:
> __hid_request in hid_hw_request
> drivers/hid/hid-picolcd_leds.c, 56:
> hid_hw_request in picolcd_leds_set
> drivers/hid/hid-picolcd_leds.c, 53:
> _raw_spin_lock_irqsave in picolcd_leds_set
>
> drivers/hid/hid-core.c, 1459:
> hid_alloc_report_buf(GFP_KERNEL) in __hid_request
> ./include/linux/hid.h, 1051:
> __hid_request in hid_hw_request
> drivers/hid/hid-picolcd_lcd.c, 49:
> hid_hw_request in picolcd_set_contrast
> drivers/hid/hid-picolcd_lcd.c, 46:
> _raw_spin_lock_irqsave in picolcd_set_contrast
>
> drivers/hid/hid-core.c, 1459:
> hid_alloc_report_buf(GFP_KERNEL) in __hid_request
> ./include/linux/hid.h, 1051:
> __hid_request in hid_hw_request
> drivers/hid/hid-picolcd_core.c, 245:
> hid_hw_request in picolcd_reset
> drivers/hid/hid-picolcd_core.c, 235:
> _raw_spin_lock_irqsave in picolcd_reset
>
> drivers/hid/hid-core.c, 1459:
> hid_alloc_report_buf(GFP_KERNEL) in __hid_request
> ./include/linux/hid.h, 1051:
> __hid_request in hid_hw_request
> drivers/hid/hid-picolcd_core.c, 111:
> hid_hw_request in picolcd_send_and_wait
> drivers/hid/hid-picolcd_core.c, 100:
> _raw_spin_lock_irqsave in picolcd_send_and_wait
>
> hid_alloc_report_buf(GFP_KERNEL) can sleep at runtime.
>
> To fix these bugs, hid_hw_request() is called without holding the
> spinlock.
>
> These bugs are found by a static analysis tool STCheck written by myself.
>
> Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
> ---
> drivers/hid/hid-picolcd_core.c | 4 ++--
> drivers/hid/hid-picolcd_lcd.c | 6 ++++--
> drivers/hid/hid-picolcd_leds.c | 6 ++++--
> 3 files changed, 10 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/hid/hid-picolcd_core.c b/drivers/hid/hid-picolcd_core.c
> index 1b5c63241af0..55d1892daa15 100644
> --- a/drivers/hid/hid-picolcd_core.c
> +++ b/drivers/hid/hid-picolcd_core.c
> @@ -99,8 +99,8 @@ struct picolcd_pending *picolcd_send_and_wait(struct hid_device *hdev,
> work = NULL;
> } else {
> data->pending = work;
> - hid_hw_request(data->hdev, report, HID_REQ_SET_REPORT);
> spin_unlock_irqrestore(&data->lock, flags);
> + hid_hw_request(data->hdev, report, HID_REQ_SET_REPORT);
> wait_for_completion_interruptible_timeout(&work->ready, HZ*2);
> spin_lock_irqsave(&data->lock, flags);
> data->pending = NULL;
> @@ -233,8 +233,8 @@ int picolcd_reset(struct hid_device *hdev)
> spin_unlock_irqrestore(&data->lock, flags);
> return -ENODEV;
> }
> - hid_hw_request(hdev, report, HID_REQ_SET_REPORT);
> spin_unlock_irqrestore(&data->lock, flags);
> + hid_hw_request(hdev, report, HID_REQ_SET_REPORT);
>
> error = picolcd_check_version(hdev);
> if (error)
> diff --git a/drivers/hid/hid-picolcd_lcd.c b/drivers/hid/hid-picolcd_lcd.c
> index 0c4b76de8ae5..1fd291674ffe 100644
> --- a/drivers/hid/hid-picolcd_lcd.c
> +++ b/drivers/hid/hid-picolcd_lcd.c
> @@ -26,6 +26,7 @@ static int picolcd_get_contrast(struct lcd_device *ldev)
> static int picolcd_set_contrast(struct lcd_device *ldev, int contrast)
> {
> struct picolcd_data *data = lcd_get_data(ldev);
> + int status;
> struct hid_report *report = picolcd_out_report(REPORT_CONTRAST, data->hdev);
> unsigned long flags;
>
> @@ -35,9 +36,10 @@ static int picolcd_set_contrast(struct lcd_device *ldev, int contrast)
> data->lcd_contrast = contrast & 0x0ff;
> spin_lock_irqsave(&data->lock, flags);
> hid_set_field(report->field[0], 0, data->lcd_contrast);
> - if (!(data->status & PICOLCD_FAILED))
> - hid_hw_request(data->hdev, report, HID_REQ_SET_REPORT);
> + status = data->status;
> spin_unlock_irqrestore(&data->lock, flags);
> + if (!(status & PICOLCD_FAILED))
> + hid_hw_request(data->hdev, report, HID_REQ_SET_REPORT);
> return 0;
> }
>
> diff --git a/drivers/hid/hid-picolcd_leds.c b/drivers/hid/hid-picolcd_leds.c
> index 6b505a753511..6652aa6b98dd 100644
> --- a/drivers/hid/hid-picolcd_leds.c
> +++ b/drivers/hid/hid-picolcd_leds.c
> @@ -32,6 +32,7 @@
> void picolcd_leds_set(struct picolcd_data *data)
> {
> struct hid_report *report;
> + int status;
> unsigned long flags;
>
> if (!data->led[0])
> @@ -42,9 +43,10 @@ void picolcd_leds_set(struct picolcd_data *data)
>
> spin_lock_irqsave(&data->lock, flags);
> hid_set_field(report->field[0], 0, data->led_state);
> - if (!(data->status & PICOLCD_FAILED))
> - hid_hw_request(data->hdev, report, HID_REQ_SET_REPORT);
> + status = data->status;
> spin_unlock_irqrestore(&data->lock, flags);
> + if (!(status & PICOLCD_FAILED))
> + hid_hw_request(data->hdev, report, HID_REQ_SET_REPORT);
> }
>
> static void picolcd_led_set_brightness(struct led_classdev *led_cdev,

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