| Message ID | 20191218140537.12193-1-baijiaju1990@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | media: sti: bdisp: fix a possible sleep-in-atomic-context bug in bdisp_device_run() | expand |
Hi Jia_Ju, This is a good finding. See my remarks below. On 18/12/2019 3:05 PM, Jia-Ju Bai wrote: > The driver may sleep while holding a spinlock. > The function call path (from bottom to top) in Linux 4.19 is: > > drivers/media/platform/sti/bdisp/bdisp-hw.c, 385: > msleep in bdisp_hw_reset > drivers/media/platform/sti/bdisp/bdisp-v4l2.c, 341: > bdisp_hw_reset in bdisp_device_run > drivers/media/platform/sti/bdisp/bdisp-v4l2.c, 317: > _raw_spin_lock_irqsave in bdisp_device_run > > To fix this bug, msleep() is replaced with mdelay(). > > This bug is found by a static analysis tool STCheck written by myself. > > Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com> > --- > drivers/media/platform/sti/bdisp/bdisp-hw.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/media/platform/sti/bdisp/bdisp-hw.c b/drivers/media/platform/sti/bdisp/bdisp-hw.c > index 4372abbb5950..1a56348805a2 100644 > --- a/drivers/media/platform/sti/bdisp/bdisp-hw.c > +++ b/drivers/media/platform/sti/bdisp/bdisp-hw.c > @@ -382,7 +382,7 @@ int bdisp_hw_reset(struct bdisp_dev *bdisp) > for (i = 0; i < POLL_RST_MAX; i++) { > if (readl(bdisp->regs + BLT_STA1) & BLT_STA1_IDLE) > break; > - msleep(POLL_RST_DELAY_MS); > + mdelay(POLL_RST_DELAY_MS); In general, use of mdelay is discouraged. Here we can use udelay instead of, with a max value of MAX_UDELAY_MS which is 2 on ARM. So, instead of running 50 (POLL_RST_MAX) times a 20ms (POLL_RST_DELAY_MS) delay, we can run 500 times a 2ms (2000us) delay. The following changes shall be fine: POLL_RST_MAX 50 --> 500 POLL_RST_DELAY_MS 20 --> 2 mdelay(POLL_RST_DELAY_MS) --> udelay(POLL_RST_DELAY_MS * 1000) BR Fabien > } > if (i == POLL_RST_MAX) > dev_err(bdisp->dev, "Reset timeout\n");
And calling readl_poll_timeout_atomic() would probably be better :) On 19/12/2019 10:01 AM, Fabien DESSENNE wrote: > Hi Jia_Ju, > > > This is a good finding. See my remarks below. > > > On 18/12/2019 3:05 PM, Jia-Ju Bai wrote: >> The driver may sleep while holding a spinlock. >> The function call path (from bottom to top) in Linux 4.19 is: >> >> drivers/media/platform/sti/bdisp/bdisp-hw.c, 385: >> msleep in bdisp_hw_reset >> drivers/media/platform/sti/bdisp/bdisp-v4l2.c, 341: >> bdisp_hw_reset in bdisp_device_run >> drivers/media/platform/sti/bdisp/bdisp-v4l2.c, 317: >> _raw_spin_lock_irqsave in bdisp_device_run >> >> To fix this bug, msleep() is replaced with mdelay(). >> >> This bug is found by a static analysis tool STCheck written by myself. >> >> Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com> >> --- >> drivers/media/platform/sti/bdisp/bdisp-hw.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/media/platform/sti/bdisp/bdisp-hw.c >> b/drivers/media/platform/sti/bdisp/bdisp-hw.c >> index 4372abbb5950..1a56348805a2 100644 >> --- a/drivers/media/platform/sti/bdisp/bdisp-hw.c >> +++ b/drivers/media/platform/sti/bdisp/bdisp-hw.c >> @@ -382,7 +382,7 @@ int bdisp_hw_reset(struct bdisp_dev *bdisp) >> for (i = 0; i < POLL_RST_MAX; i++) { >> if (readl(bdisp->regs + BLT_STA1) & BLT_STA1_IDLE) >> break; >> - msleep(POLL_RST_DELAY_MS); >> + mdelay(POLL_RST_DELAY_MS); > > In general, use of mdelay is discouraged. Here we can use udelay > instead of, with a max value of MAX_UDELAY_MS which is 2 on ARM. > > So, instead of running 50 (POLL_RST_MAX) times a 20ms > (POLL_RST_DELAY_MS) delay, we can run 500 times a 2ms (2000us) delay. > > The following changes shall be fine: > > POLL_RST_MAX 50 --> 500 > > POLL_RST_DELAY_MS 20 --> 2 > > mdelay(POLL_RST_DELAY_MS) --> udelay(POLL_RST_DELAY_MS * 1000) > > > BR > > Fabien > > >> } >> if (i == POLL_RST_MAX) >> dev_err(bdisp->dev, "Reset timeout\n");
diff --git a/drivers/media/platform/sti/bdisp/bdisp-hw.c b/drivers/media/platform/sti/bdisp/bdisp-hw.c index 4372abbb5950..1a56348805a2 100644 --- a/drivers/media/platform/sti/bdisp/bdisp-hw.c +++ b/drivers/media/platform/sti/bdisp/bdisp-hw.c @@ -382,7 +382,7 @@ int bdisp_hw_reset(struct bdisp_dev *bdisp) for (i = 0; i < POLL_RST_MAX; i++) { if (readl(bdisp->regs + BLT_STA1) & BLT_STA1_IDLE) break; - msleep(POLL_RST_DELAY_MS); + mdelay(POLL_RST_DELAY_MS); } if (i == POLL_RST_MAX) dev_err(bdisp->dev, "Reset timeout\n");
The driver may sleep while holding a spinlock. The function call path (from bottom to top) in Linux 4.19 is: drivers/media/platform/sti/bdisp/bdisp-hw.c, 385: msleep in bdisp_hw_reset drivers/media/platform/sti/bdisp/bdisp-v4l2.c, 341: bdisp_hw_reset in bdisp_device_run drivers/media/platform/sti/bdisp/bdisp-v4l2.c, 317: _raw_spin_lock_irqsave in bdisp_device_run To fix this bug, msleep() is replaced with mdelay(). This bug is found by a static analysis tool STCheck written by myself. Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com> --- drivers/media/platform/sti/bdisp/bdisp-hw.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)