[PATCH] serial: core: Shut down a suspended port on removal

[PATCH] serial: core: Shut down a suspended port on removal

[Phil Rosenthal via B4 Relay]

From: Phil Rosenthal <phil@phil.gs>

Commit 810d467c11f0 ("serial: core: shut down initialized port on
removal") calls uart_shutdown() from serial_core_remove_one_port() only
if the port is initialized.  A port that is removed while suspended is
not: uart_suspend_port() clears its initialized flag, sets its suspended
flag and keeps its transmit buffer.  Nothing clears the flag or frees
the buffer on removal, so both stay in the line's uart_state.

If the line is reused, the next uart_resume_port() for the new port
finds the suspended flag set and starts the port up although nobody has
opened it.  If the uart_driver is unregistered instead, the buffer is
leaked, as uart_unregister_driver() does not free it.

Call uart_shutdown() whether or not the port is initialized.  For a port
that is not initialized it leaves the hardware alone, and it always
clears the suspended flag and frees the transmit buffer.

Fixes: 810d467c11f0 ("serial: core: shut down initialized port on removal")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/sashiko-outbox-164404@kernel.org
Assisted-by: LLM sparse
Signed-off-by: Phil Rosenthal <phil@phil.gs>
---
Greg asked for this as a follow-up to 810d467c11f0 in the thread on my
duplicate of that fix [1].

Tested in a QEMU guest on tty-next 8db79ea07a67 with KASAN.  To remove
a port while it is suspended, a test module registers a polled 8250
platform port, which becomes the console, and after the port has been
opened and closed it calls serial8250_suspend_port(), as a system
suspend would, and then removes the port.  It prints the line's
uart_state before and after removal:

  810d467c11f0 alone (on tty-next 36844ea19656):
    before removal: initialized=0 suspended=1 xmit_buf=allocated
    after removal:  initialized=0 suspended=1 xmit_buf=allocated

  With this patch:
    before removal: initialized=0 suspended=1 xmit_buf=allocated
    after removal:  initialized=0 suspended=0 xmit_buf=NULL

The cases 810d467c11f0 fixes still pass: an 8250_pci port with INTx
unbound after its console was opened and closed (IRQ freed, rebinding
restores the console and getty), and a polled MMIO console port removed
after being opened and closed.  A port held open across removal and a
console that was never opened also still work.  W=1, sparse and
checkpatch --strict are clean.

Not tested: removal during a real system suspend.  What happens on a
reused line at the next resume is from reading the code.

[1] https://lore.kernel.org/r/2026101433-refuse-unbiased-4b63@gregkh

AI assistance: an LLM coding assistant (Claude, model claude-opus-5-5,
in Claude Code) wrote the patch and the test module, and built and ran
the test kernels.  I reviewed it.
---
 drivers/tty/serial/serial_core.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 9eea8d1a0e8a0e60d8af9b56c917954f5dc45f0e..a234217487d3718ae5e9c533112c2020a3aca946 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -3246,9 +3246,7 @@ static void serial_core_remove_one_port(struct uart_driver *drv,
 
 	scoped_guard(mutex, &port->mutex) {
 		port->console = false;
-
-		if (tty_port_initialized(port))
-			uart_shutdown(NULL, state);
+		uart_shutdown(NULL, state);
 	}
 
 	/*

---
base-commit: 8db79ea07a67b126c773da6efdc00066000daeb8
change-id: 20261014-serial-remove-suspended-da773bc28dc5

Best regards,
-- 
Phil Rosenthal <phil@phil.gs>

Re: [PATCH] serial: core: Shut down a suspended port on removal

[sashiko-bot]

> From: Phil Rosenthal <phil@phil.gs>
> 
> Commit 810d467c11f0 ("serial: core: shut down initialized port on
> removal") calls uart_shutdown() from serial_core_remove_one_port() only
> if the port is initialized.  A port that is removed while suspended is
> not: uart_suspend_port() clears its initialized flag, sets its suspended
> flag and keeps its transmit buffer.  Nothing clears the flag or frees
> the buffer on removal, so both stay in the line's uart_state.
> 
> If the line is reused, the next uart_resume_port() for the new port
> finds the suspended flag set and starts the port up although nobody has
> opened it.  If the uart_driver is unregistered instead, the buffer is
> leaked, as uart_unregister_driver() does not free it.
> 
> Call uart_shutdown() whether or not the port is initialized.  For a port
> that is not initialized it leaves the hardware alone, and it always
> clears the suspended flag and frees the transmit buffer.
> 
> Fixes: 810d467c11f0 ("serial: core: shut down initialized port on removal")
> Cc: stable@vger.kernel.org
> Link: https://lore.kernel.org/r/sashiko-outbox-164404@kernel.org
> Assisted-by: LLM sparse
> Signed-off-by: Phil Rosenthal <phil@phil.gs>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261014-serial-remove-suspended-v1-1-fda644ab5f89@phil.gs?part=1