RE: [PATCH v3] cfi: fix deadloop in cfi_cmdset_0002.c do_write_buffer

["Tokunori Ikegami" <ikegami_to@yahoo.co.jp>]

> -----Original Message-----
> From: linux-mtd [mailto:linux-mtd-bounces@lists.infradead.org] On Behalf
> Of Boris Brezillon
> Sent: Friday, March 1, 2019 12:42 AM
> To: liujian (CE)
> Cc: Tokunori Ikegami; keescook@chromium.org; bbrezillon@kernel.org;
> ikegami@allied-telesis.co.jp; richard@nod.at;
> linux-kernel@vger.kernel.org; marek.vasut@gmail.com;
> linux-mtd@lists.infradead.org; computersforpeace@gmail.com;
> dwmw2@infradead.org; vigneshr@ti.com
> Subject: Re: [PATCH v3] cfi: fix deadloop in cfi_cmdset_0002.c
> do_write_buffer
> 
> On Thu, 28 Feb 2019 15:12:15 +0000
> "liujian (CE)" <liujian56@huawei.com> wrote:
> 
> > > -----Original Message-----
> > > From: Tokunori Ikegami [mailto:ikegami.t@gmail.com]
> > > Sent: Thursday, February 28, 2019 10:26 PM
> > > To: liujian (CE) <liujian56@huawei.com>; dwmw2@infradead.org;
> > > computersforpeace@gmail.com; bbrezillon@kernel.org;
> > > marek.vasut@gmail.com; richard@nod.at;
> joakim.tjernlund@infinera.com;
> > > ikegami@allied-telesis.co.jp; keescook@chromium.org; vigneshr@ti.com
> > > Cc: linux-mtd@lists.infradead.org; linux-kernel@vger.kernel.org
> > > Subject: RE: [PATCH v3] cfi: fix deadloop in cfi_cmdset_0002.c
> do_write_buffer
> > >
> > >
> > >
> > > > -----Original Message-----
> > > > From: linux-mtd [mailto:linux-mtd-bounces@lists.infradead.org] On
> > > > Behalf Of Liu Jian
> > > > Sent: Tuesday, February 26, 2019 11:01 PM
> > > > To: dwmw2@infradead.org; computersforpeace@gmail.com;
> > > > bbrezillon@kernel.org; marek.vasut@gmail.com; richard@nod.at;
> > > > joakim.tjernlund@infinera.com; ikegami@allied-telesis.co.jp;
> > > > keescook@chromium.org; vigneshr@ti.com
> > > > Cc: linux-mtd@lists.infradead.org; liujian56@huawei.com;
> > > > linux-kernel@vger.kernel.org
> > > > Subject: [PATCH v3] cfi: fix deadloop in cfi_cmdset_0002.c
> > > > do_write_buffer
> > > >
> > > > In function do_write_buffer(), in the for loop, there is a case
> > > > chip_ready() returns 1 while chip_good() returns 0, so it never break
> > > > the loop.
> > > > To fix this, chip_good() is enough and it should timeout if it stay
> > > > bad for a while.
> > > >
> > > > Fixes: dfeae1073583("mtd: cfi_cmdset_0002: Change write buffer to
> > > > check correct value")
> > > > Signed-off-by: Yi Huaijie <yihuaijie@huawei.com>
> > > > Signed-off-by: Liu Jian <liujian56@huawei.com>
> > > > Reviewed-by: Tokunori Ikegami <ikegami_to@yahoo.co.jp>
> > > > ---
> > > > v2->v3:
> > > > Follow Vignesh's advice:
> > > > add one more check for check_good() even when time_after() returns
> true.
> > > >
> > > >  drivers/mtd/chips/cfi_cmdset_0002.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/mtd/chips/cfi_cmdset_0002.c
> > > > b/drivers/mtd/chips/cfi_cmdset_0002.c
> > > > index 72428b6..3da2376 100644
> > > > --- a/drivers/mtd/chips/cfi_cmdset_0002.c
> > > > +++ b/drivers/mtd/chips/cfi_cmdset_0002.c
> > > > @@ -1876,7 +1876,7 @@ static int __xipram do_write_buffer(struct
> > > > map_info *map, struct flchip *chip,
> > > >  			continue;
> > > >  		}
> > > >
> > > > -		if (time_after(jiffies, timeo) && !chip_ready(map, adr))
> > > > +		if (time_after(jiffies, timeo) && !chip_good(map, adr,
> > > > datum))
> > >
> > >   Just another idea to understand easily.
> > >
> > >     unsigned long now = jiffies;
> > >
> > >     if (chip_good(map, adr, datum)) {
> > >         xip_enable(map, chip, adr);
> > >         goto op_done;
> > >     }
> > >
> > >     if (time_after(now, timeo) {
> > >         break;
> > >     }
> > >
> >
> > Thank you~. It is more easier to understand！
> > If there are no other comments, I will send new patch again ):
> 
> Except this version no longer does what Vignesh suggested. See how you
> no longer test if chip_good() is true if time_after() returns true. So,
> imagine the thread entering this function is preempted just after the
> first chip_good() test, and resumed a few ms later. time_after() will
> return true, but chip_good() might also return true, and you ignore it.

I think that the following 3 versions will be worked for time_after() as a same result and follow the Vignesh-san suggestion.

1. Original Vignesh-san suggestion

	if (chip_good(map, adr, datum)) {
		xip_enable(map, chip, adr);
		goto op_done;
	}

	if (time_after(jiffies, timeo)) {
		/* Test chip_good() if TRUE incorrectly again so write failure by time_after() can be avoided. */
		if (chip_good(map, adr, datum)) {
			xip_enable(map, chip, adr);
			goto op_done;
		}
		break;
	}

2. Liujian-san v3 patch

	/* Test chip_good() if FALSE correctly so write failure by time_after() can be avoided. */
	if (time_after(jiffies, timeo) && !chip_good(map, adr))
		break;

	if (chip_good(map, adr, datum)) {
		xip_enable(map, chip, adr);
		goto op_done;
	}

3. My idea

	/* Save current jiffies value before chip_good() to avoid write failure by time_after() without testing chip_good() again. */
	unsigned long now = jiffies;

	if (chip_good(map, adr, datum)) {
		xip_enable(map, chip, adr);
		goto op_done;
	}

	if (time_after(now, timeo))
		break;

          Note: Some brackets have been fixed from the previous mail.

Regards,
Ikegami

> 
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