Messages in this thread | | | Date | Fri, 11 Oct 2013 12:02:47 +0100 | From | Will Deacon <> | Subject | Re: BUG report about ipt_do_table( ) |
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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: > https://www.google.com/#q=cortex+a15+microarchitecture > > the first: [PDF] Exploring the Design of the Cortex-A15 Processor - ARM > > 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?
Will
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