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usb: device_next: cdc_acm: bound poll_out backpressure wait #2

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usb: device_next: cdc_acm: bound poll_out backpressure wait #2

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11 changes: 10 additions & 1 deletion subsys/usb/device_next/class/usbd_cdc_acm.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1009,6 +1009,7 @@ static void cdc_acm_poll_out(const struct device *dev, const unsigned char c)
struct cdc_acm_uart_data *const data = dev->data;
k_spinlock_key_t key;
uint32_t wrote;
int retries = 20;

while (true) {
key = k_spin_lock(&data->lock);
Expand All @@ -1019,7 +1020,15 @@ static void cdc_acm_poll_out(const struct device *dev, const unsigned char c)
break;
}

if (k_is_in_isr() || !data->flow_ctrl) {
/* Bounded wait: with an attached-but-stalled host session (macOS
* ceases IN polling for minutes at a time), an unbounded sleep-retry
* here makes every console write take the full stall duration. Any
* thread that logs (event text loggers, assert reporting) then backs
* up its own queues and cascades into a system-wide com livelock.
* After ~20 ms of backpressure, treat the console as best-effort and
* discard, exactly like the detached (!flow_ctrl) case below.
*/
if (k_is_in_isr() || !data->flow_ctrl || retries-- <= 0) {
LOG_WRN_ONCE("Ring buffer full, discard data");
break;
}
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