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serial: 8250: always disable IRQ during THRE test 

commit 039d492637 ("serial: 8250: Toggle IER bits on only after irq
has been set up") moved IRQ setup before the THRE test, in combination
with commit 205d300aea ("serial: 8250: change lock order in
serial8250_do_startup()") the interrupt handler can run during the
test and race with its IIR reads. This can produce wrong THRE test
results and cause spurious registration of the
serial8250_backup_timeout timer. Unconditionally disable the IRQ for
the short duration of the test and re-enable it afterwards to avoid
the race.

Fixes: 039d492637 ("serial: 8250: Toggle IER bits on only after irq has been set up")
Depends-on: 205d300aea ("serial: 8250: change lock order in serial8250_do_startup()")
Cc: stable <stable@kernel.org>
Signed-off-by: Peng Zhang <zhangpeng.00@bytedance.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Signed-off-by: Alban Bedel <alban.bedel@lht.dlh.de>
Tested-by: Maximilian Lueer <maximilian.lueer@lht.dlh.de>
Link: https://patch.msgid.link/20260224121639.579404-1-alban.bedel@lht.dlh.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Peng Zhang 2026-02-24 13:16:39 +01:00 committed by Greg Kroah-Hartman
parent a424a34b8f
commit 24b98e8664
1 changed files with 2 additions and 4 deletions
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6
drivers/tty/serial/8250/8250_port.c
View File

@ -2147,8 +2147,7 @@ static void serial8250_THRE_test(struct uart_port *port)
if (up->port.flags & UPF_NO_THRE_TEST)
return;
if (port->irqflags & IRQF_SHARED)
disable_irq_nosync(port->irq);
disable_irq(port->irq);
/*
* Test for UARTs that do not reassert THRE when the transmitter is idle and the interrupt
@ -2170,8 +2169,7 @@ static void serial8250_THRE_test(struct uart_port *port)
serial_port_out(port, UART_IER, 0);
}
if (port->irqflags & IRQF_SHARED)
enable_irq(port->irq);
enable_irq(port->irq);
/*
* If the interrupt is not reasserted, or we otherwise don't trust the iir, setup a timer to