2018-03-18 14:51:52

by Jia-Ju Bai

Subject: [PATCH] char: pcmcia: cm4000_cs: Replace mdelay with usleep_range in set_protocol

set_protocol() is never called in atomic context.

The call chains ending up at set_protocol() are:
[1] set_protocol() <- monitor_card()
[2] set_protocol() <- cmm_ioctl()
monitor_card() is only set in setup_timer(), and cmm_ioctl() is only
set as ".unlocked_ioctl" in file_operations structure "cm4000_fops".

Despite never getting called from atomic context, set_protocol() calls
mdelay(10), i.e. busy wait for 10ms.
That is not necessary and can be replaced with usleep_range to
avoid busy waiting.

This is found by a static analysis tool named DCNS written by myself.

Signed-off-by: Jia-Ju Bai <[email protected]>
---
drivers/char/pcmcia/cm4000_cs.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/char/pcmcia/cm4000_cs.c b/drivers/char/pcmcia/cm4000_cs.c
index cd53771..56fc671 100644
--- a/drivers/char/pcmcia/cm4000_cs.c
+++ b/drivers/char/pcmcia/cm4000_cs.c
@@ -530,7 +530,7 @@ static int set_protocol(struct cm4000_dev *dev, struct ptsreq *ptsreq)
DEBUGP(5, dev, "NumRecBytes is valid\n");
break;
}
- mdelay(10);
+ usleep_range(10000, 11000);
}
if (i == 100) {
DEBUGP(5, dev, "Timeout waiting for NumRecBytes getting "
@@ -546,7 +546,7 @@ static int set_protocol(struct cm4000_dev *dev, struct ptsreq *ptsreq)
DEBUGP(2, dev, "NumRecBytes = %i\n", num_bytes_read);
break;
}
- mdelay(10);
+ usleep_range(10000, 11000);
}

/* check whether it is a short PTS reply? */
--
1.9.1

2018-03-18 15:21:46

by Harald Welte

Subject: Re: [PATCH] char: pcmcia: cm4000_cs: Replace mdelay with usleep_range in set_protocol

Hi Jia-Ju Bai,

On Sun, Mar 18, 2018 at 10:49:57PM +0800, Jia-Ju Bai wrote:
> This is found by a static analysis tool named DCNS written by myself.

nice catch!

> Signed-off-by: Jia-Ju Bai <[email protected]>

Acked-by: Harald Welte <[email protected]>

--
- Harald Welte <[email protected]> http://laforge.gnumonks.org/
============================================================================
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2018-10-01 11:02:28

by Dominik Brodowski

Subject: Re: [PATCH] char: pcmcia: cm4000_cs: Replace mdelay with usleep_range in set_protocol

On Sun, Mar 18, 2018 at 04:12:10PM +0100, Harald Welte wrote:
> Hi Jia-Ju Bai,
>
> On Sun, Mar 18, 2018 at 10:49:57PM +0800, Jia-Ju Bai wrote:
> > This is found by a static analysis tool named DCNS written by myself.
>
> nice catch!
>
> > Signed-off-by: Jia-Ju Bai <[email protected]>
>
> Acked-by: Harald Welte <[email protected]>

Applied to pcmcia-next.

Thanks,
Dominik