Re: [PATCH 4/7] IB/srp: Fix a potential queue overflow in an error path

[Bart Van Assche <bart.vanassche-XdAiOPVOjttBDgjK7y7TUQ@public.gmane.org>]

On 11/03/2015 09:36 AM, Sagi Grimberg wrote:
> On 28/10/2015 00:02, Bart Van Assche wrote:
>> Wait until memory registration has finished in the srp_queuecommand()
>> error path before invalidating memory regions to avoid a send queue
>> overflow.
>
> This looks backwards to me... Why do we even post anything on our
> queue-pair to begin with if we got an unsupported sg list?
>
> Can't we perform a simple sanity check on the sg list instead?

Hello Sagi,

There is one memory descriptor pool per RDMA channel and RDMA channels 
are typically used by more than one CPU. This means that memory 
registration for more than one command can happen concurrently from a 
single memory descriptor pool. This is why checking how many memory 
descriptors are left before memory registration occurs wouldn't be 
sufficient.

Bart.
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