Re: [RFC PATCH 1/2] ALSA: virtio: account staged capture reads before RX refill

[sashiko-bot@kernel.org]

> The RX callback holds the queue lock across a batch of completions. A
> reader that has copied samples can wait for that lock in ACK before its
> consumed bytes are removed from capture_ready. A later completion in the
> same batch can then reject data using stale ring occupancy.
> 
> Account the staged read under the substream lock before acquiring the RX
> queue lock. Release that lock before taking the queue and substream locks
> in their established order to refill requests.
> 
> Once accounting is committed, latch refill errors as XRUN and return
> success from ACK. A negative return would make ALSA restore appl_ptr while
> the driver retained the consumed-byte accounting. Keep pre-commit errors,
> ring-capacity checks, and normal period-work scheduling unchanged.
> 
> Source-extracted host and kernel fixtures reproduce the stale-capacity
> race and post-commit ALSA pointer rollback. The candidate preserves wrapped
> data and pointer accounting. KASAN/lockdep QEMU lifecycle checks passed.
> The fixtures substitute selected backend helpers and do not independently
> establish physical-device acceptance.
> 
> This follows pending staged capture support, whose introducing patch has
> no upstream commit ID for a Fixes tag yet.
> 
> Link: https://lore.kernel.org/all/rfc-v2-vz-capture-compat-1.b9ab4c1540dc4691@gmail.com/
> Assisted-by: LLM
> Signed-off-by: Joonho Lee <mynameisjune111@gmail.com>

Sashiko has reviewed this patch and found no issues.

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