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SubjectRE: [PATCH] cfi: fix deadloop in cfi_cmdset_0002.c do_write_buffer
Date
> From: Boris Brezillon <bbrezillon@kernel.org> 
> Sent: Sunday, February 3, 2019 12:35 AM
> > +Przemyslaw
> >
> > On Fri, 1 Feb 2019 07:30:39 +0800
> > Liu Jian <liujian56@huawei.com> 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.
> >
> > Looks like Przemyslaw reported and fixed the same problem.
> >
> > >
> > > Fixes: dfeae1073583(mtd: cfi_cmdset_0002: Change write buffer to
> > > check correct value)
> >
> > Can you put the Fixes tag on a single, and the format is
> >
> > Fixes: <hash> ("message")
> >
> > > Signed-off-by: Yi Huaijie <yihuaijie@huawei.com>
> > > Signed-off-by: Liu Jian <liujian56@huawei.com>
> >
> > [1]http://patchwork.ozlabs.org/patch/1025566/
> >
> > > ---
> > > 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;
> > > +
> > > /* Latency issues. Drop the lock, wait a while and retry */
> > > UDELAY(map, chip, adr, 1);
> > > }
> >
>
> BTW, the patch itself looks good to me. Ikegami, can you confirm it does the right thing?
>
> Thanks,
>
> Boris
>

One comment to this patch. If value is written incorrectly quickly we will be
stuck in the loop even though nothing is going to change. For example a value was
written incorrectly after 1us, the loop was set to 1ms, function will return
after 1ms, this solution is not optimized for performance. I considered same
when working on this change and decided to do it different way.

Regards,
Przemek

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