ipc: fix recursive data queue locking on SMP

rt_data_queue_pop() holds the data queue spinlock while updating the ring
state, then calls rt_data_queue_len(). The length function tries to acquire
the same non-recursive spinlock again, causing an SMP deadlock when a pop
leaves the queue non-empty.

Add a private _data_queue_len_nolock() helper for callers which already hold
the queue lock. Keep the public rt_data_queue_len() protected by one spinlock
acquisition.

This does not change the public API, ABI, queue state transitions, low-water
mark wakeups, or event callback behavior.

Tested on a four-core Spacemit K1 with cyclic HDMI playback and by building the
SMP QEMU Virt64 RISC-V BSP with generic audio, Intel HDA and VirtIO Sound.

Signed-off-by: GuEe-GUI <[email protected]>

0 files changed, 0 insertions, 0 deletions