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

[Boris Brezillon <boris.brezillon@collabora.com>]

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.