Re: [patch 1/4] firewire: fix race of bus reset with request transmission

[Stefan Richter <stefanr@s5r6.in-berlin.de>]

I wrote:
> Contexts which access an instance of struct fw_transaction are:
>  1. the submitter, until it inserted the packet which is embedded in the
>     transaction into the AT req DMA,
>  2. the AsReqTrContext tasklet when the request packet was acked by the
>     responder node or transmission to the responder failed,
>  3. the AsRspRcvContext tasklet when it found a request which matched
>     an incoming response,
>  4. the card->flush_timer when it picks up timed-out transactions to
>     cancel them,
>  5. the bus reset tasklet when it cancels transactions (this access is
>     eliminated by this patch),
>  6. a process which shuts down an fw_card (unregisters it from fw-core
>     when the controller is unbound from fw-ohci) --- although in this
>     case there shouldn't really be any transactions anymore because we
>     wait until all card users finished their business with the card.
> 
> All of these contexts run concurrently (except for the 6th, presumably).

PS:  Actually the three tasklets (2nd, 3rd, 5th context) are all
scheduled on the same CPU, hence are serialized.  Therefore

> The 5th looks safe against 2nd, 3rd [...] but is unsafe against 1st.

5th is serialized against 4th and 6th by lock protection of
card->transaction_list accesses.
-- 
Stefan Richter
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