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SubjectRE: [PATCH v2] cfi: fix deadloop in cfi_cmdset_0002.c do_write_buffer
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> -----Original Message-----
> From: Vignesh R [mailto:vigneshr@ti.com]
> Sent: Friday, February 22, 2019 1:59 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
> Cc: linux-mtd@lists.infradead.org; linux-kernel@vger.kernel.org
> 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@huawei.com>
> > Signed-off-by: Liu Jian <liujian56@huawei.com>
> > Reviewed-by: Tokunori Ikegami <ikegami_to@yahoo.co.jp>
> > ---
> > 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
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