linux-kernel - Re: [PATCH -v3] x86: do not free zero sized per cpu areas

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Date:	Fri, 19 Mar 2010 16:24:40 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org,
	Ian Campbell <ian.campbell@...rix.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH -v3] x86: do not free zero sized per cpu areas

On 03/19/2010 03:21 PM, H. Peter Anvin wrote:
> On 03/19/2010 03:18 PM, Yinghai Lu wrote:
>> From: Ian Campbell <ian.campbell@...rix.com>
>>
>> This avoids an infinite loop in free_early_partial().
>>
>> Add a warning to free_early_partial to catch future problems.
>>
>> -v3: according to hpa, don't bother caller.
>>
>> Signed-off-by: Ian Campbell <ian.campbell@...rix.com>
>> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
>> Cc: Peter Zijlstra <peterz@...radead.org>
>> Cc: Ingo Molnar <mingo@...e.hu>
>> ---
>>  kernel/early_res.c             |    5 +++++
>>  1 files changed, 5 insertions(+), 0 deletions(-)
>>
>> diff --git a/kernel/early_res.c b/kernel/early_res.c
>> index 3cb2c66..f3a861b 100644
>> --- a/kernel/early_res.c
>> +++ b/kernel/early_res.c
>> @@ -333,6 +333,11 @@ void __init free_early_partial(u64 start, u64 end)
>>  	struct early_res *r;
>>  	int i;
>>  
>> +	if (WARN_ONCE(start >= end,
>> +		      "free_early_partial got wrong start/end %#llx/%#llx\n",
>> +		      start, end))
>> +		return;
>> +
>>  try_next:
>>  	i = find_overlapped_early(start, end);
>>  	if (i >= max_early_res)
> 
> No, that's wrong.
> 
> The workaround is still needed for the case of equality to avoid the
> infinite loop.
> 
> So you need an:
> 
> 	if (start == end)
> 		return;
> 

confused, do you mean like this
if (start < end), find_overlapped_early will stop the loop.

From: Ian Campbell <ian.campbell@...rix.com>

This avoids an infinite loop in free_early_partial().

Add a warning to free_early_partial to catch future problems.

-v3: according to hpa, don't bother caller.

Signed-off-by: Ian Campbell <ian.campbell@...rix.com>
Signed-off-by: Yinghai Lu <yinghai@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...e.hu>
---
 kernel/early_res.c |    8 ++++++++
 1 file changed, 8 insertions(+)

Index: linux-2.6/kernel/early_res.c
===================================================================
--- linux-2.6.orig/kernel/early_res.c
+++ linux-2.6/kernel/early_res.c
@@ -333,6 +333,14 @@ void __init free_early_partial(u64 start
 	struct early_res *r;
 	int i;
 
+	if (start >= end) {
+		WARN_ONCE(1,
+		      "free_early_partial got wrong start/end %#llx/%#llx\n",
+		      start, end);
+
+		return;
+	}
+
 try_next:
 	i = find_overlapped_early(start, end);
 	if (i >= max_early_res)
--
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