Re: [PATCH 0/2] sg: fix races during device removal (v2)

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

I wrote:
> You can do a little trick here and combine this flag with the counter t:
> Simply say t = 1 for "this device is open and has no outstanding
> transactions yet".  Then increment and decrement for requests and
> responses.  Also do t-- once on close().  Then t == 0 means "closed and
> all transactions completed".  And any t != 0 means of course "there are
> t - 1 transactions pending".  You could also shift it all by one and say
> "t == -1 means device closed and 0 transactions pending" but the former
> way allows you to use the kref API.  (However, if you ever need to know
> whether the device is open or closed, independently whether there are
> transactions pending or not, then you can't fold this "open?" flag into
> the transaction counter t.)

Also, of course you can't use the kref API for this counter t if you
want to read the number of pending transactions somewhere.  Use an
atomic_t then, or an int whose accessors are serialized by a lock.
-- 
Stefan Richter
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http://arcgraph.de/sr/