Re: [PATCH] serial: 8250: prevent DMA callbacks from restarting a closing port

[sashiko-bot@kernel.org]

> Disabling UART interrupts does not prevent a DMA completion callback from
> running. A TX callback can submit more data or enable THRI after shutdown
> has cleared IER. An RX callback can also submit a new receive if data is
> still present. A callback already running when terminate_sync() starts
> can therefore restart the channel whose buffers are about to be freed.
> 
> Mark DMA as shutting down under the port lock when disabling interrupts.
> Check that state under the same lock in the completion callbacks and
> submission paths, so callbacks either finish before the shutdown boundary
> or leave the channel stopped. The DMA provider's synchronization still
> has to drain callbacks before release_dma() frees their resources.
> 
> Apply the same boundary to OMAP, which has its own shutdown and DMA
> callbacks but shares the channel-request and release helpers. Check it
> in MediaTek's receive callback after taking the port lock as well: its
> earlier private shutdown check cannot serialize a callback that has
> already passed that check. Reset the state after requesting channels
> on the next open. Leave the Broadcom integrated DMA path, which manages
> its own shutdown state, unchanged.
> 
> 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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