Re: [PATCH v9 8/8] serial: 8250: retain DMA resources when termination fails

[sashiko-bot@kernel.org]

> serial8250_release_dma() ignores the return from dmaengine_terminate_sync()
> before freeing the coherent RX buffer, unmapping the TX FIFO and releasing
> the channels. If the provider fails to stop a channel, the DMAengine
> wrapper returns the error without synchronizing its callbacks. Hardware
> or a detached callback can then access the released storage and state.
> 
> Checking the error and returning early would not preserve their lifetime:
> serial core frees the TX FIFO after the driver's shutdown callback returns,
> and port removal can then release the callback context as well.
> 
> Require successful synchronous termination of both channels before
> releasing any DMA resources. Retry failed channels after a sleep outside
> the port lock, leaving channels that have already stopped and drained
> alone. Keep the shutdown gate and storage reservation in place throughout
> the retries.
> 
> Start retries with a 1 ms sleep and double it up to one second. This
> makes short-lived failures responsive while bounding sustained retry
> activity; neither delay is a hardware timeout. Report the initial failure,
> rate-limit ongoing failures with the elapsed time and current RX/TX error
> codes, and report recovery once both channels have stopped and drained.
> 
> A permanently failed DMA engine blocks close or removal. This deliberately
> retains the buffers, mappings, channels and callback context until the
> provider can establish that they are no longer in use.
> 
> Fixes: 9ee4b83e51f7 ("serial: 8250: Add support for dmaengine")
> Signed-off-by: James Hilliard <james.hilliard1@gmail.com>

Sashiko has reviewed this patch and found no issues.

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