RE: [PATCH v2] cfi: fix deadloop in cfi_cmdset_0002.c do_write_buffer

[liujian (CE)]

> -----Original Message-----
> From: Vignesh R [mailto:vigneshr@xxxxxx]
> Sent: Friday, February 22, 2019 1:59 PM
> To: liujian (CE) <liujian56@xxxxxxxxxx>; dwmw2@xxxxxxxxxxxxx;
> computersforpeace@xxxxxxxxx; bbrezillon@xxxxxxxxxx;
> marek.vasut@xxxxxxxxx; richard@xxxxxx; joakim.tjernlund@xxxxxxxxxxxx;
> ikegami@xxxxxxxxxxxxxxxxxxxx; keescook@xxxxxxxxxxxx
> Cc: linux-mtd@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v2] cfi: fix deadloop in cfi_cmdset_0002.c do_write_buffer
> 
> 
> 
> On 20/02/19 2:17 AM, Liu Jian wrote:
> > 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@xxxxxxxxxx>
> > Signed-off-by: Liu Jian <liujian56@xxxxxxxxxx>
> > Reviewed-by: Tokunori Ikegami <ikegami_to@xxxxxxxxxxx>
> > ---
> > v1->v2:
> > change git log, put the Fixes tag on a single line
> >
> >  drivers/mtd/chips/cfi_cmdset_0002.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/mtd/chips/cfi_cmdset_0002.c
> > b/drivers/mtd/chips/cfi_cmdset_0002.c
> > index 72428b6..818e94b 100644
> > --- a/drivers/mtd/chips/cfi_cmdset_0002.c
> > +++ b/drivers/mtd/chips/cfi_cmdset_0002.c
> > @@ -1876,14 +1876,14 @@ static int __xipram do_write_buffer(struct
> map_info *map, struct flchip *chip,
> >  			continue;
> >  		}
> >
> > -		if (time_after(jiffies, timeo) && !chip_ready(map, adr))
> > -			break;
> > -
> >  		if (chip_good(map, adr, datum)) {
> >  			xip_enable(map, chip, adr);
> >  			goto op_done;
> >  		}
> >
> > +		if (time_after(jiffies, timeo))
> > +			break;
> > +
> 
> It is quite possible that this thread might be pre-empted just after
> chip_good() check but before before time_after(). If the thread, then resumes
> execution after timeo has elasped then, this code will wrongly indicate write
> failure.
> 
> To avoid this case, you should add one more check for check_good() even when
> time_after() returns true. Something like:
> 
> 	if (time_after(jiffies, timeo)) {
> 		if (chip_good(map, adr, datum)) {
> 			xip_enable(map, chip, adr);
> 			goto op_done;
> 		}
> 		break;
> 	}
> 
So,  the patch should like this ?

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))
                        break;

                if (chip_good(map, adr, datum)) {



Any other opinions?
If there are no other comments, I will send a patch again

> 
> >  		/* Latency issues. Drop the lock, wait a while and retry */
> >  		UDELAY(map, chip, adr, 1);
> >  	}
> >
> 
> --
> Regards
> Vignesh