[ofa-general] [PATCH][REPOST] drivers/infiniband/ulp/srpt: Fix target data corruption

[Vladislav Bolkhovitin]

Vladislav Bolkhovitin wrote:
> davem at systemfabricworks.com wrote:
> 
>> This is an updated version of [PATCH] drivers/infiniband/ulp/srpt: Fix
>> target data corruption
>>
>> It was pointed out to me that the code to round up to a power of 2 was
>> not as clean as it should be, plus I extracted two unrelated patches and
>> submitted them separately.
>>
>> =====================================================================
>>
>>    Change the local buffer allocator to use a spin-lock protected linked
>>    list instead of an array of atomic_t used/free variables.  The 
>> atomic_t
>>    code was open to a multi-thread race between test and set.  This has
>>    been observed with the result that the same data buffer was used for
>>    more than one SCSI operation, either writing the wrong data to the 
>> disk
>>    or sending the wrong data to the initiator.
> 
> 
> I, as a main SCST developer and implementor, would suggest to completely 
> remove internal memory management from the SRPT driver and use SCST 
> memory management instead. It will provide the following advantages:
> 
> 1. Simplify SRPT driver and completely remove such kind of bugs.
> 
> 2. Make SRPT target driver compatible with scst_user module, i.e. will 
> allow to use SRPT target driver with backstorage devices, implemented in 
> user space. Usual example of such devices is a VTL (Virtual Tape Library).
> 
> 3. (Most likely, since I'm not too familiar with SRPT drivers internals, 
> but for me it looks like so) Allow SRPT driver to reliably work with 
> many outstanding commands with big data transfer sizes (>=1MB)
> 
> 4. Might improve performance by caching and reusing already allocated 
> and "iomaped" to Infiniband hardware SG vectors. Vu knows the details, 
> we discussed them with him. It will require some minor SCST 
> modifications (extending its interface with target drivers), but I'm 
> willing to make them if somebody ask for it.

Oops, I forgot to mention, probably, the most important advantage:

5. Make SRPT target driver compatible with the upcoming zero-copy cache 
usage, where the system cache will be used directly without the extra copy.

> Vlad
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