[lkml]   [2013]   [Oct]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRE: BUG report about ipt_do_table( )
Hi  Will, 

I am happy to notify that our stability test has passed,
And this Crash don't happen again,
So seems this patch work now .

We has merged it into our release SW .
Could I know if this patch will be delivered into kernel
Mainline by you ?

Thanks again !

-----Original Message-----
From: Wang, Yalin
Sent: Friday, October 11, 2013 7:15 PM
To: 'Will Deacon'
Cc: '';; Peng, Arthur; Zhang, Bojie; Gu, Youcai 1 (EXT); Alevoor, Raghavendra 2
Subject: RE: BUG report about ipt_do_table( )

Hi Will,

Thanks for your clarification .

I have merged the patch,
And need wait some time to get
The test result ,
You know that this BUG is not easy to reproduce, It's very infrequent.
Maybe we need run several times stability test to Make sure the patch works .

I will update to you the result as soon as possible !


-----Original Message-----
From: Will Deacon []
Sent: Friday, October 11, 2013 7:03 PM
To: Wang, Yalin
Cc: '';; Peng, Arthur; Zhang, Bojie; Gu, Youcai 1 (EXT); Alevoor, Raghavendra 2
Subject: Re: BUG report about ipt_do_table( )

On Fri, Oct 11, 2013 at 02:50:24AM +0100, Wang, Yalin wrote:
> Hi Will,

Hello again,

> Maybe I know your meaning ,
> If it use spinlock to protected the shared data, The bug will not
> happen, because spinlock will Use DSB( ) to sync .

Actually, the dsb is for something else (the sev). It is the smp_mb() call which guarantees the ordering of critical sections with respect to spinlock operations.

> Unluckily, here, it use a special seqcount_t( ) (see get_counters( )
> function)

Well, there is a comment about a write_lock being held, so you should be ok if that's true. The issue I saw was with the newinfo population, as I described in my earlier mail.

> To make sure there is no others using the old data, Before release the
> old data, this is much like RCU Work, but RCU use rcu_assign_pointer(
> ) --> Which use smp_wmb( ) , so it's safe, am I right ?

RCU is safe. There are *many* weakly ordered architectures on which Linux runs, so I don't think you have to worry too much about the core data structures and locking/synchronisation/atomic primitives. The major scope for errors is in lockless code, where the barrier usage is explicit.

> In my patch, I use mb( ), because this macro Is DSB( ) , while
> smp_wmb( ) is DMS( ), I just think DSB is much strict than DMS, mmm..
> so , DSM( ) or DMS ( ) are both ok ?

I think you're getting confused with your barriers. We have two memory barriers on ARM: dmb and dsb. dmb is sufficient to enforce ordering of observability. dsb is used to enforce completion.

> The whitepaper I use is here:
> the first: [PDF] Exploring the Design of the Cortex-A15 Processor -
> I just search in Google, and you know that qcom don't release Much
> document about its krait cpu's micro architecture details, I just use
> cortex-a15 for a reference, I am not sure if their pipeline (
> load/store unit) are the same,

I think the lawyers would have a field day if the pipelines were the same!
You really can't use an A15 slide-deck to infer micro-architectural details about Krait.

Please can you test the patch I sent you yesterday?


 \ /
  Last update: 2013-10-17 04:01    [W:0.094 / U:2.928 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site