From: Maciej Andrzejewski ICEYE Date: Thu, 5 Mar 2026 12:37:51 +0000 (+0100) Subject: serial: uartlite: fix PM runtime usage count underflow on probe X-Git-Tag: v7.0-rc5~16^2~10 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=d54801cd509515f674a5aac1d3ea1401d2a05863;p=thirdparty%2Fkernel%2Flinux.git serial: uartlite: fix PM runtime usage count underflow on probe ulite_probe() calls pm_runtime_put_autosuspend() at the end of probe without holding a corresponding PM runtime reference for non-console ports. During ulite_assign(), uart_add_one_port() triggers uart_configure_port() which calls ulite_pm() via uart_change_pm(). For non-console ports, the UART core performs a balanced get/put cycle: uart_change_pm(ON) -> ulite_pm() -> pm_runtime_get_sync() +1 uart_change_pm(OFF) -> ulite_pm() -> pm_runtime_put_autosuspend() -1 This leaves no spare reference for the pm_runtime_put_autosuspend() at the end of probe. The PM runtime core prevents the count from actually going below zero, and instead triggers a "Runtime PM usage count underflow!" warning. For console ports the bug is masked: the UART core skips the uart_change_pm(OFF) call, so the UART core's unbalanced get happens to pair with probe's trailing put. Add pm_runtime_get_noresume() before pm_runtime_enable() to take an explicit probe-owned reference that the trailing pm_runtime_put_autosuspend() can release. This ensures a correct usage count regardless of whether the port is a console. Fixes: 5bbe10a6942d ("tty: serial: uartlite: Add runtime pm support") Cc: stable Signed-off-by: Maciej Andrzejewski ICEYE Link: https://patch.msgid.link/20260305123746.4152800-1-maciej.andrzejewski@m-works.net Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/tty/serial/uartlite.c b/drivers/tty/serial/uartlite.c index 39c1fd1ff9ce..6240c3d4dfd7 100644 --- a/drivers/tty/serial/uartlite.c +++ b/drivers/tty/serial/uartlite.c @@ -878,6 +878,7 @@ of_err: pm_runtime_use_autosuspend(&pdev->dev); pm_runtime_set_autosuspend_delay(&pdev->dev, UART_AUTOSUSPEND_TIMEOUT); pm_runtime_set_active(&pdev->dev); + pm_runtime_get_noresume(&pdev->dev); pm_runtime_enable(&pdev->dev); ret = ulite_assign(&pdev->dev, id, res->start, irq, pdata);