Re: [PATCH v2 4/4] dmaengine: dw: synchronize completion callbacks

[sashiko-bot@kernel.org]

> The controller tasklet can remove a descriptor from active_list and
> invoke its callback outside the channel lock. Terminating the channel
> does not wait for that callback, and there is no device_synchronize
> hook. A client can therefore reuse callback state or release its buffers
> after dmaengine_synchronize() while an old callback still uses them.
> 
> Disable and re-enable the controller tasklet from device_synchronize,
> outside the channel lock. Disabling waits for an executing tasklet,
> including descriptors it already removed from the channel lists. After
> termination, a later tasklet run cannot acquire another descriptor from
> the terminated channel. Clients must continue to exclude new submissions
> on that channel until synchronization finishes.
> 
> The tasklet is shared, so other channels may schedule it while this wait
> is in progress. Preserve those pending runs: tasklet_kill() temporarily
> owns the scheduling bit and can consume a concurrent scheduling request,
> leaving controller interrupts masked. The disable/enable pair leaves the
> scheduling bit and pending tasklet queue intact. Other channels' hardware
> transfers continue, though their callbacks may be briefly deferred.
> 
> Reported-by: Sashiko <sashiko-bot@kernel.org>
> Closes: https://lore.kernel.org/r/sashiko-outbox-180707@kernel.org
> Cc: stable@vger.kernel.org
> Signed-off-by: James Hilliard <james.hilliard1@gmail.com>

Sashiko has reviewed this patch and found no issues.

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