This closes a reference and memory leak when multiple CPUs are enabling echocan
on a single channel in parallel.
The essential problem is that the call to try_module_get() is not serialized.
Two separate threads can come into ioctl_echocan() on the same channel, they
coordinate via the dahdi_chan.lock to release any current echocan, but then both
create a new echocan state, bump the reference on the module, and the last one
through will actually attach the new state to the channel. The earlier reference
/ memory is leaked.
I tried to conceive of a way to fix this leak without adding a new lock, but the
choices where calling throught the function pointers with dahdi_chan.lock.
Otherwise I needed to change the semantics of echocan_create /free which would
ripple through the hardware echocan modules.
Signed-off-by: Shaun Ruffell <sruffell@digium.com>
Signed-off-by: Russ Meyerriecks <rmeyerriecks@digium.com>
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