Patch added to scsi-misc-2.6: [SCSI] libosd: Fix blk_put_request locking again

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[SCSI] libosd: Fix blk_put_request locking again

So libosd has decided to sacrifice some code simplicity for the sake of a clean API. One of these things is the possibility for users to call osd_end_request, in any condition at any state. This opens up some problems with calling blk_put_request when out-side of the completion callback but calling __blk_put_request when detecting a from-completion state.

The current hack was working just fine until exofs decided to operate on all devices in parallel and wait for the sum of the requests, before deallocating all osd-requests at once. There are two new possible cases
1. All request in a group are deallocated as part of the last request's async-done, request_queue is locked.
2. All request in a group where executed asynchronously, but de-allocation was delayed to after the async-done, in the context of another thread. Async execution but request_queue is not locked.

The solution I chose was to separate the deallocation of the osd_request which has the information users need, from the deallocation of the internal(2) requests which impose the locking problem. The internal block-requests are freed unconditionally inside the async-done-callback, when we know the queue is always locked. If at osd_end_request time we still have a bock-request, then we know it did not come from within an async-done-callback and we can call the regular blk_put_request.

The internal requests were used for carrying error information after execution. This information is now copied to osd_request members for later analysis by user code.

The external API and behaviour was unchanged, except now it really supports what was previously advertised.

Reported-by Vineet Agarwal <[email protected]>

Signed-off-by Boaz Harrosh <[email protected]>

Cc Stable Tree <[email protected]>

Signed-off-by James Bottomley <[email protected]>