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 <[email protected]>
Signed-off-by: Liu Jian <[email protected]>
Reviewed-by: Tokunori Ikegami <[email protected]>
---
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))
break;
if (chip_good(map, adr, datum)) {
--
2.7.4
> -----Original Message-----
> From: linux-mtd [mailto:[email protected]] On Behalf
> Of Liu Jian
> Sent: Tuesday, February 26, 2019 11:01 PM
> To: [email protected]; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]; [email protected];
> [email protected]; [email protected]
> Cc: [email protected]; [email protected];
> [email protected]
> 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 <[email protected]>
> Signed-off-by: Liu Jian <[email protected]>
> Reviewed-by: Tokunori Ikegami <[email protected]>
> ---
> 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;
}
Regards,
Ikegami
> break;
>
> if (chip_good(map, adr, datum)) {
> --
> 2.7.4
>
>
> ______________________________________________________
> Linux MTD discussion mailing list
> http://lists.infradead.org/mailman/listinfo/linux-mtd/
> -----Original Message-----
> From: Tokunori Ikegami [mailto:[email protected]]
> Sent: Thursday, February 28, 2019 10:26 PM
> To: liujian (CE) <[email protected]>; [email protected];
> [email protected]; [email protected];
> [email protected]; [email protected]; [email protected];
> [email protected]; [email protected]; [email protected]
> Cc: [email protected]; [email protected]
> Subject: RE: [PATCH v3] cfi: fix deadloop in cfi_cmdset_0002.c do_write_buffer
>
>
>
> > -----Original Message-----
> > From: linux-mtd [mailto:[email protected]] On
> > Behalf Of Liu Jian
> > Sent: Tuesday, February 26, 2019 11:01 PM
> > To: [email protected]; [email protected];
> > [email protected]; [email protected]; [email protected];
> > [email protected]; [email protected];
> > [email protected]; [email protected]
> > Cc: [email protected]; [email protected];
> > [email protected]
> > 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 <[email protected]>
> > Signed-off-by: Liu Jian <[email protected]>
> > Reviewed-by: Tokunori Ikegami <[email protected]>
> > ---
> > 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 ):
Best Regards,
Liujian
> Regards,
> Ikegami
>
> > break;
> >
> > if (chip_good(map, adr, datum)) {
> > --
> > 2.7.4
> >
> >
> > ______________________________________________________
> > Linux MTD discussion mailing list
> > http://lists.infradead.org/mailman/listinfo/linux-mtd/
On Thu, 28 Feb 2019 15:12:15 +0000
"liujian (CE)" <[email protected]> wrote:
> > -----Original Message-----
> > From: Tokunori Ikegami [mailto:[email protected]]
> > Sent: Thursday, February 28, 2019 10:26 PM
> > To: liujian (CE) <[email protected]>; [email protected];
> > [email protected]; [email protected];
> > [email protected]; [email protected]; [email protected];
> > [email protected]; [email protected]; [email protected]
> > Cc: [email protected]; [email protected]
> > Subject: RE: [PATCH v3] cfi: fix deadloop in cfi_cmdset_0002.c do_write_buffer
> >
> >
> >
> > > -----Original Message-----
> > > From: linux-mtd [mailto:[email protected]] On
> > > Behalf Of Liu Jian
> > > Sent: Tuesday, February 26, 2019 11:01 PM
> > > To: [email protected]; [email protected];
> > > [email protected]; [email protected]; [email protected];
> > > [email protected]; [email protected];
> > > [email protected]; [email protected]
> > > Cc: [email protected]; [email protected];
> > > [email protected]
> > > 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 <[email protected]>
> > > Signed-off-by: Liu Jian <[email protected]>
> > > Reviewed-by: Tokunori Ikegami <[email protected]>
> > > ---
> > > 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.
Hi Ikegami,
On Fri, 1 Mar 2019 23:51:16 +0900
"Tokunori Ikegami" <[email protected]> wrote:
> > 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.
Let me show you how they are different:
>
> 1. Original Vignesh-san suggestion
>
> if (chip_good(map, adr, datum)) {
> xip_enable(map, chip, adr);
> goto op_done;
> }
--> thread preempted here
==> chip_good() test becomes valid here
--> thread resumed here, but timeout has expired
>
> if (time_after(jiffies, timeo)) {
you enter this branch
> /* Test chip_good() if TRUE incorrectly again so write failure by time_after() can be avoided. */
> if (chip_good(map, adr, datum)) {
chip_good() returns true
> 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. */
--> thread preempted here
==> chip_good() test becomes valid here
--> thread resumed here, but timeout has expired
> if (time_after(jiffies, timeo) && !chip_good(map, adr))
You do not enter this branch because the chip_good() test is done once
more in case of timeout.
> 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;
> }
>
--> thread preempted here
==> chip_good() test becomes valid here
--> thread resumed here, but timeout has expired
> if (time_after(now, timeo))
You do enter this branch, and erroneously report a failure.
> break;
>
See now why your version is not correct?
Regards,
Boris
[...]
>>>>> 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 <[email protected]>
>>>>> Signed-off-by: Liu Jian <[email protected]>
>>>>> Reviewed-by: Tokunori Ikegami <[email protected]>
>>>>> ---
>>>>> 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.
>
As Boris explained above version 3 does not really follow my
suggestion... Please see below
> 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;
> }
>
Right, here we check chip_good() once _even when time_after() is true_
to avoid _spurious_ timeout
> 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;
> }
>
This is a better version of 1
> 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;
> }
>
What if thread gets pre-empted at this point and is re-scheduled exactly
after timeo jiffies have elapsed? Below check would be true and exit loop
> if (time_after(now, timeo))
> break;
>
So, code does not check for check chip_good() after timeoout has
elapsed. But chip_good() might be true at this point. Therefore leading
to spurious timeout. So this version is still not right.
> Note: Some brackets have been fixed from the previous mail.
>
Hi Boris-san,
> -----Original Message-----
> From: linux-mtd [mailto:[email protected]] On Behalf
> Of Boris Brezillon
> Sent: Saturday, March 2, 2019 1:07 AM
> To: Tokunori Ikegami
> Cc: 'Tokunori Ikegami'; [email protected]; [email protected];
> [email protected]; [email protected];
> [email protected]; [email protected];
> [email protected]; [email protected];
> [email protected]; 'liujian (CE)'; [email protected]
> Subject: Re: [PATCH v3] cfi: fix deadloop in cfi_cmdset_0002.c
> do_write_buffer
>
> Hi Ikegami,
>
> On Fri, 1 Mar 2019 23:51:16 +0900
> "Tokunori Ikegami" <[email protected]> wrote:
>
> > > 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.
>
> Let me show you how they are different:
>
> >
> > 1. Original Vignesh-san suggestion
> >
> > if (chip_good(map, adr, datum)) {
> > xip_enable(map, chip, adr);
> > goto op_done;
> > }
>
> --> thread preempted here
> ==> chip_good() test becomes valid here
> --> thread resumed here, but timeout has expired
>
> >
> > if (time_after(jiffies, timeo)) {
>
> you enter this branch
>
> > /* Test chip_good() if TRUE incorrectly again so write
> failure by time_after() can be avoided. */
> > if (chip_good(map, adr, datum)) {
>
> chip_good() returns true
>
> > 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. */
>
> --> thread preempted here
> ==> chip_good() test becomes valid here
> --> thread resumed here, but timeout has expired
>
> > if (time_after(jiffies, timeo) && !chip_good(map, adr))
>
> You do not enter this branch because the chip_good() test is done once
> more in case of timeout.
>
> > 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;
> > }
> >
>
> --> thread preempted here
> ==> chip_good() test becomes valid here
> --> thread resumed here, but timeout has expired
>
> > if (time_after(now, timeo))
>
> You do enter this branch, and erroneously report a failure.
I do not think that it is not entered here since the value timeo is compare
with the saved value now before the chip_bood() by time_after().
>
> > break;
> >
>
> See now why your version is not correct?
>
> Regards,
>
> Boris
>
> ______________________________________________________
> Linux MTD discussion mailing list
> http://lists.infradead.org/mailman/listinfo/linux-mtd/
> [...]
> >>>>> 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 <[email protected]>
> >>>>> Signed-off-by: Liu Jian <[email protected]>
> >>>>> Reviewed-by: Tokunori Ikegami <[email protected]>
> >>>>> ---
> >>>>> 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.
> >
>
> As Boris explained above version 3 does not really follow my
> suggestion... Please see below
>
> > 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;
> > }
> >
>
>
> Right, here we check chip_good() once _even when time_after() is true_
> to avoid _spurious_ timeout
>
> > 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;
> > }
> >
>
> This is a better version of 1
>
> > 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;
> > }
> >
>
> What if thread gets pre-empted at this point and is re-scheduled exactly
> after timeo jiffies have elapsed? Below check would be true and exit loop
I think that the jiffies value now is save before chip_good() so below check would be false and not exit loop.
Regards,
Ikegami
>
> > if (time_after(now, timeo))
> > break;
> >
>
> So, code does not check for check chip_good() after timeoout has
> elapsed. But chip_good() might be true at this point. Therefore leading
> to spurious timeout. So this version is still not right.
>
> > Note: Some brackets have been fixed from the previous mail.
> >
>
> ______________________________________________________
> Linux MTD discussion mailing list
> http://lists.infradead.org/mailman/listinfo/linux-mtd/
On Sat, 2 Mar 2019 01:59:41 +0900
"Tokunori Ikegami" <[email protected]> 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 <[email protected]>
> > >>>>> Signed-off-by: Liu Jian <[email protected]>
> > >>>>> Reviewed-by: Tokunori Ikegami <[email protected]>
> > >>>>> ---
> > >>>>> 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.
> > >
> >
> > As Boris explained above version 3 does not really follow my
> > suggestion... Please see below
> >
> > > 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;
> > > }
> > >
> >
> >
> > Right, here we check chip_good() once _even when time_after() is
> > true_ to avoid _spurious_ timeout
> >
> > > 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;
> > > }
> > >
> >
> > This is a better version of 1
> >
> > > 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;
> > > }
> > >
> >
> > What if thread gets pre-empted at this point and is re-scheduled
> > exactly after timeo jiffies have elapsed? Below check would be true
> > and exit loop
>
> I think that the jiffies value now is save before chip_good() so
> below check would be false and not exit loop.
True, I overlooked that part, and so Vignesh did. This proves one
thing: code is not easier to follow with your version. IMO, if we want
to make things clear, we should add a comment to Liujian's explaining
why the extra test after time_after(jiffies, timeo) is needed.
The "mtd: " prefix is still missing. Should be "mtd: cfi: ". If you
send a new version, please fix that.
Thanks,
Boris
On Tue, 26 Feb 2019 22:00:48 +0800
Liu Jian <[email protected]> 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 <[email protected]>
> Signed-off-by: Liu Jian <[email protected]>
> Reviewed-by: Tokunori Ikegami <[email protected]>
> ---
> 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))
> break;
>
> if (chip_good(map, adr, datum)) {
On 01-Mar-19 11:25 PM, Tokunori Ikegami 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 <[email protected]>
>>>>>>>>> Signed-off-by: Liu Jian <[email protected]>
>>>>>>>>> Reviewed-by: Tokunori Ikegami <[email protected]>
>>>>>>>>> ---
>>>>>>>>> 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.
>>>>>
>>>>
>>>> As Boris explained above version 3 does not really follow my
>>>> suggestion... Please see below
>>>>
>>>>> 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;
>>>>> }
>>>>>
>>>>
>>>>
>>>> Right, here we check chip_good() once _even when time_after() is
>>>> true_ to avoid _spurious_ timeout
>>>>
>>>>> 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;
>>>>> }
>>>>>
>>>>
>>>> This is a better version of 1
>>>>
>>>>> 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;
>>>>> }
>>>>>
>>>>
>>>> What if thread gets pre-empted at this point and is re-scheduled
>>>> exactly after timeo jiffies have elapsed? Below check would be true
>>>> and exit loop
>>>
>>> I think that the jiffies value now is save before chip_good() so
>>> below check would be false and not exit loop.
>>
Ok, I get it now.
>> True, I overlooked that part, and so Vignesh did. This proves one
>> thing: code is not easier to follow with your version. IMO, if we want
>> to make things clear, we should add a comment to Liujian's explaining
>> why the extra test after time_after(jiffies, timeo) is needed.
>
> I see so I am okay with the change of Liujian-san v3 patch.
> Also agree with the comment to be added.
>
Right, I like the current patch from Liujian, because its more
consistent with the existing code in this file.
Liujian, Could you re-post with a comment added as suggested above?
Regards
Vignesh