* [RESEND PATCH v2] memory-hotplug: fix store_mem_state() return value
[not found] <20160831150105.GB26702@kroah.com>
@ 2016-08-31 15:44 ` Reza Arbab
2016-08-31 20:25 ` Andrew Morton
0 siblings, 1 reply; 8+ messages in thread
From: Reza Arbab @ 2016-08-31 15:44 UTC (permalink / raw)
To: Greg Kroah-Hartman, Andrew Morton, Vlastimil Babka,
Vitaly Kuznetsov, David Rientjes, Yaowei Bai, Joonsoo Kim,
Dan Williams, Xishi Qiu, David Vrabel, Chen Yucong,
Andrew Banman, linux-mm, linux-kernel
Attempting to online memory which is already online will cause this:
1. store_mem_state() called with buf="online"
2. device_online() returns 1 because device is already online
3. store_mem_state() returns 1
4. calling code interprets this as 1-byte buffer read
5. store_mem_state() called again with buf="nline"
6. store_mem_state() returns -EINVAL
Example:
$ cat /sys/devices/system/memory/memory0/state
online
$ echo online > /sys/devices/system/memory/memory0/state
-bash: echo: write error: Invalid argument
Fix the return value of store_mem_state() so this doesn't happen.
Signed-off-by: Reza Arbab <arbab@linux.vnet.ibm.com>
---
Andrew et al, Greg asked that this come in through the -mm tree, as
you know this code better than him.
drivers/base/memory.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index 1cea0ba..8e385ea 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -359,7 +359,7 @@ store_mem_state(struct device *dev,
err:
unlock_device_hotplug();
- if (ret)
+ if (ret < 0)
return ret;
return count;
}
--
1.8.3.1
--
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^ permalink raw reply related [flat|nested] 8+ messages in thread
* Re: [RESEND PATCH v2] memory-hotplug: fix store_mem_state() return value
2016-08-31 15:44 ` [RESEND PATCH v2] memory-hotplug: fix store_mem_state() return value Reza Arbab
@ 2016-08-31 20:25 ` Andrew Morton
2016-08-31 21:06 ` David Rientjes
0 siblings, 1 reply; 8+ messages in thread
From: Andrew Morton @ 2016-08-31 20:25 UTC (permalink / raw)
To: Reza Arbab
Cc: Greg Kroah-Hartman, Vlastimil Babka, Vitaly Kuznetsov,
David Rientjes, Yaowei Bai, Joonsoo Kim, Dan Williams, Xishi Qiu,
David Vrabel, Chen Yucong, Andrew Banman, linux-mm, linux-kernel
On Wed, 31 Aug 2016 10:44:01 -0500 Reza Arbab <arbab@linux.vnet.ibm.com> wrote:
> Attempting to online memory which is already online will cause this:
>
> 1. store_mem_state() called with buf="online"
> 2. device_online() returns 1 because device is already online
> 3. store_mem_state() returns 1
> 4. calling code interprets this as 1-byte buffer read
> 5. store_mem_state() called again with buf="nline"
> 6. store_mem_state() returns -EINVAL
>
> Example:
>
> $ cat /sys/devices/system/memory/memory0/state
> online
> $ echo online > /sys/devices/system/memory/memory0/state
> -bash: echo: write error: Invalid argument
>
> Fix the return value of store_mem_state() so this doesn't happen.
So.. what *does* happen after the patch? Is some sort of failure still
reported? Or am I correct in believing that the operation will appear
to have succeeded? If so, is that desirable?
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^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [RESEND PATCH v2] memory-hotplug: fix store_mem_state() return value
2016-08-31 20:25 ` Andrew Morton
@ 2016-08-31 21:06 ` David Rientjes
2016-08-31 23:38 ` Reza Arbab
0 siblings, 1 reply; 8+ messages in thread
From: David Rientjes @ 2016-08-31 21:06 UTC (permalink / raw)
To: Andrew Morton
Cc: Reza Arbab, Greg Kroah-Hartman, Vlastimil Babka,
Vitaly Kuznetsov, Yaowei Bai, Joonsoo Kim, Dan Williams,
Xishi Qiu, David Vrabel, Chen Yucong, Andrew Banman, linux-mm,
linux-kernel
On Wed, 31 Aug 2016, Andrew Morton wrote:
> > Attempting to online memory which is already online will cause this:
> >
> > 1. store_mem_state() called with buf="online"
> > 2. device_online() returns 1 because device is already online
> > 3. store_mem_state() returns 1
> > 4. calling code interprets this as 1-byte buffer read
> > 5. store_mem_state() called again with buf="nline"
> > 6. store_mem_state() returns -EINVAL
> >
> > Example:
> >
> > $ cat /sys/devices/system/memory/memory0/state
> > online
> > $ echo online > /sys/devices/system/memory/memory0/state
> > -bash: echo: write error: Invalid argument
> >
> > Fix the return value of store_mem_state() so this doesn't happen.
>
> So.. what *does* happen after the patch? Is some sort of failure still
> reported? Or am I correct in believing that the operation will appear
> to have succeeded? If so, is that desirable?
>
It's not desirable, before commit 4f3549d72 this would have returned
EINVAL since __memory_block_change_state() does not see the state as
MEM_OFFLINE when the write is done. The correct fix is for
store_mem_state() to return -EINVAL when device_online() returns non-zero.
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^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [RESEND PATCH v2] memory-hotplug: fix store_mem_state() return value
2016-08-31 21:06 ` David Rientjes
@ 2016-08-31 23:38 ` Reza Arbab
2016-09-01 0:03 ` David Rientjes
0 siblings, 1 reply; 8+ messages in thread
From: Reza Arbab @ 2016-08-31 23:38 UTC (permalink / raw)
To: David Rientjes
Cc: Andrew Morton, Greg Kroah-Hartman, Vlastimil Babka,
Vitaly Kuznetsov, Yaowei Bai, Joonsoo Kim, Dan Williams,
Xishi Qiu, David Vrabel, Chen Yucong, Andrew Banman, linux-mm,
linux-kernel
On Wed, Aug 31, 2016 at 02:06:14PM -0700, David Rientjes wrote:
>The correct fix is for store_mem_state() to return -EINVAL when
>device_online() returns non-zero.
Let me put it to you this way--which one of these sysfs operations is
behaving correctly?
# cd /sys/devices/system/memory/memory0
# cat online
1
# echo 1 > online; echo $?
0
or
# cd /sys/devices/system/memory/memory0
# cat state
online
# echo online > state; echo $?
-bash: echo: write error: Invalid argument
1
One of them should change to match the other.
--
Reza Arbab
--
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^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [RESEND PATCH v2] memory-hotplug: fix store_mem_state() return value
2016-08-31 23:38 ` Reza Arbab
@ 2016-09-01 0:03 ` David Rientjes
2016-09-01 0:17 ` Reza Arbab
0 siblings, 1 reply; 8+ messages in thread
From: David Rientjes @ 2016-09-01 0:03 UTC (permalink / raw)
To: Reza Arbab
Cc: Andrew Morton, Greg Kroah-Hartman, Vlastimil Babka,
Vitaly Kuznetsov, Yaowei Bai, Joonsoo Kim, Dan Williams,
Xishi Qiu, David Vrabel, Chen Yucong, Andrew Banman,
Seth Jennings, linux-mm, linux-kernel
On Wed, 31 Aug 2016, Reza Arbab wrote:
> > The correct fix is for store_mem_state() to return -EINVAL when
> > device_online() returns non-zero.
>
> Let me put it to you this way--which one of these sysfs operations is behaving
> correctly?
>
> # cd /sys/devices/system/memory/memory0
> # cat online
> 1
> # echo 1 > online; echo $?
> 0
>
> or
>
> # cd /sys/devices/system/memory/memory0
> # cat state
> online
> # echo online > state; echo $?
> -bash: echo: write error: Invalid argument
> 1
>
> One of them should change to match the other.
>
Nope, the return value of changing state from online to online was
established almost 11 years ago in commit 3947be1969a9. This was broken
by commit fa2be40fe7c0 ("drivers: base: use standard device online/offline
for state change") which was not intended to introduce a functional
change, but it did (memory_block_change_state() would have returned
EINVAL, device_online() does not).
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^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [RESEND PATCH v2] memory-hotplug: fix store_mem_state() return value
2016-09-01 0:03 ` David Rientjes
@ 2016-09-01 0:17 ` Reza Arbab
2016-09-01 0:28 ` David Rientjes
0 siblings, 1 reply; 8+ messages in thread
From: Reza Arbab @ 2016-09-01 0:17 UTC (permalink / raw)
To: David Rientjes
Cc: Andrew Morton, Greg Kroah-Hartman, Vlastimil Babka,
Vitaly Kuznetsov, Yaowei Bai, Joonsoo Kim, Dan Williams,
Xishi Qiu, David Vrabel, Chen Yucong, Andrew Banman,
Seth Jennings, linux-mm, linux-kernel
On Wed, Aug 31, 2016 at 05:03:25PM -0700, David Rientjes wrote:
>Nope, the return value of changing state from online to online was
>established almost 11 years ago in commit 3947be1969a9.
Fair enough. So if online-to-online is -EINVAL,
1. Shouldn't 'echo 1 > online' then also return -EINVAL?
2. store_mem_state() still needs a tweak, right? It was only returning
-EINVAL by accident, due to the convoluted sequence I listed in the
patch.
--
Reza Arbab
--
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^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [RESEND PATCH v2] memory-hotplug: fix store_mem_state() return value
2016-09-01 0:17 ` Reza Arbab
@ 2016-09-01 0:28 ` David Rientjes
2016-09-01 1:57 ` Reza Arbab
0 siblings, 1 reply; 8+ messages in thread
From: David Rientjes @ 2016-09-01 0:28 UTC (permalink / raw)
To: Reza Arbab
Cc: Andrew Morton, Greg Kroah-Hartman, Vlastimil Babka,
Vitaly Kuznetsov, Yaowei Bai, Joonsoo Kim, Dan Williams,
Xishi Qiu, David Vrabel, Chen Yucong, Andrew Banman,
Seth Jennings, linux-mm, linux-kernel
On Wed, 31 Aug 2016, Reza Arbab wrote:
> > Nope, the return value of changing state from online to online was
> > established almost 11 years ago in commit 3947be1969a9.
>
> Fair enough. So if online-to-online is -EINVAL,
online-to-online for state is -EINVAL, it has been since 2005.
> 1. Shouldn't 'echo 1 > online' then also return -EINVAL?
>
No, it's a different tunable. There's no requirement that two different
tunables that do a similar thing have the same return values: the former
existed long before device_online() and still exists for backwards
compatibility.
> 2. store_mem_state() still needs a tweak, right? It was only returning -EINVAL
> by accident, due to the convoluted sequence I listed in the patch.
>
Yes, absolutely. It returning -EINVAL for "nline" is what is accidently
preserving it's backwards compatibility :) Note that device_online()
returns 1 if already online and memory_subsys_online() returns 0 if online
in this case. So we want store_mem_state() to return -EINVAL if
device_online() returns non-zero (this was in my first email).
--
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^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [RESEND PATCH v2] memory-hotplug: fix store_mem_state() return value
2016-09-01 0:28 ` David Rientjes
@ 2016-09-01 1:57 ` Reza Arbab
0 siblings, 0 replies; 8+ messages in thread
From: Reza Arbab @ 2016-09-01 1:57 UTC (permalink / raw)
To: David Rientjes
Cc: Andrew Morton, Greg Kroah-Hartman, Vlastimil Babka,
Vitaly Kuznetsov, Yaowei Bai, Joonsoo Kim, Dan Williams,
Xishi Qiu, David Vrabel, Chen Yucong, Andrew Banman,
Seth Jennings, linux-mm, linux-kernel
On Wed, Aug 31, 2016 at 05:28:26PM -0700, David Rientjes wrote:
>> 2. store_mem_state() still needs a tweak, right? It was only
>> returning -EINVAL by accident, due to the convoluted sequence I
>> listed in the patch.
>
>Yes, absolutely. It returning -EINVAL for "nline" is what is accidently
>preserving it's backwards compatibility :) Note that device_online()
>returns 1 if already online and memory_subsys_online() returns 0 if online
>in this case. So we want store_mem_state() to return -EINVAL if
>device_online() returns non-zero (this was in my first email).
I'll spin a v3 patch to do this.
Thank you for your review!
--
Reza Arbab
--
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[not found] <20160831150105.GB26702@kroah.com>
2016-08-31 15:44 ` [RESEND PATCH v2] memory-hotplug: fix store_mem_state() return value Reza Arbab
2016-08-31 20:25 ` Andrew Morton
2016-08-31 21:06 ` David Rientjes
2016-08-31 23:38 ` Reza Arbab
2016-09-01 0:03 ` David Rientjes
2016-09-01 0:17 ` Reza Arbab
2016-09-01 0:28 ` David Rientjes
2016-09-01 1:57 ` Reza Arbab
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