linux-kernel - Re: [PATCH v2] kdump: crashk_res init check for /sys/kernel/kexec_crash

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Message-ID: <4ECCFD1E.4030908@redhat.com>
Date:	Wed, 23 Nov 2011 22:03:10 +0800
From:	Dave Young <dyoung@...hat.com>
To:	holzheu@...ux.vnet.ibm.com
CC:	heiko.carstens@...ibm.com, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org, Simon Horman <horms@...ge.net.au>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	schwidefsky@...ibm.com, akpm@...ux-foundation.org,
	Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH v2] kdump: crashk_res init check for /sys/kernel/kexec_crash_size

On 11/23/2011 09:46 PM, Michael Holzheu wrote:

> Hi Dave,
> 
> On Wed, 2011-11-23 at 21:34 +0800, Dave Young wrote:
>> On 11/23/2011 09:18 PM, Michael Holzheu wrote:
>>
>>> From: Michael Holzheu <holzheu@...ux.vnet.ibm.com>
>>>
>>> Currently it is possible to set the crash_size via the sysfs
>>> /sys/kernel/kexec_crash_size even if no crash kernel memory has
>>> been defined with the "crashkernel" parameter. In this case
>>> "crashk_res" is not initialized and crashk_res.start = crashk_res.end = 0.
>>> Unfortunately resource_size(&crashk_res) returns 1 in this case.
>>> This breaks the s390 implementation of crash_(un)map_reserved_pages().
>>>
>>> To fix the problem the correct "old_size" is now calculated in
>>> crash_shrink_memory(). "old_size is set to "0" if crashk_res is
>>> not initialized. With this change crash_shrink_memory() will do nothing,
>>> when "crashk_res" is not initialized. It will return "0" for
>>> "echo 0 > /sys/kernel/kexec_crash_size" and -EINVAL for
>>> "echo [not zero] > /sys/kernel/kexec_crash_size".
>>>
>>> In addition to that this patch also simplifies the "ret = -EINVAL"
>>> vs. "ret = 0" logic as suggested by Simon Horman.
>>>
>>> Cc: Simon Horman <horms@...ge.net.au>
>>> Signed-off-by: Michael Holzheu <holzheu@...ux.vnet.ibm.com>
>>> ---
>>>  kernel/kexec.c |   10 ++++------
>>>  1 file changed, 4 insertions(+), 6 deletions(-)
>>>
>>> --- a/kernel/kexec.c
>>> +++ b/kernel/kexec.c
>>> @@ -1131,7 +1131,7 @@ void __weak crash_free_reserved_phys_ran
>>>  int crash_shrink_memory(unsigned long new_size)
>>>  {
>>>  	int ret = 0;
>>> -	unsigned long start, end;
>>> +	unsigned long start, end, old_size;
>>
>>
>> Sorry for jump in a little late, instead of introduce a new variable,
>> why not add something like:
>>
>> if (!end)
>> 	return -EINVAL;
> 
> If the crashkernel parameter is not set, "/sys/kernel/kexec_crash_size"
> returns zero:
> 
> cat /sys/kernel/kexec_crash_size
> 0
> 
> So I think if we set it again to zero we should *not* return -EINVAL:


Thanks, I missed this case. fair enough.

Reviewed-by: Dave Young <dyoung@...hat.com>

> 
> echo 0 > /sys/kernel/kexec_crash_size
> --> Exit code should be zero in this case
> 
> Otherwise we would change the current behavior.
> 
> And besides of that, I think introducing the "old_size" variable makes
> the code more readable.
> 
> Michael
> 
> 



-- 
Thanks
Dave
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