linux-kernel - Re: [PATCH v2] serial: 8250: always disable IRQ during THRE test

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Message-ID: <CAMZfGtWhgHoYU4c2Yz5w6XCXJ0oSoJbm0_kW=YvjFENv+pDj3Q@mail.gmail.com>
Date: Thu, 16 Oct 2025 16:55:42 +0800
From: Muchun Song <songmuchun@...edance.com>
To: Peng Zhang <zhangpeng.00@...edance.com>
Cc: Greg KH <gregkh@...uxfoundation.org>, Jiri Slaby <jirislaby@...nel.org>, 
	ilpo.jarvinen@...ux.intel.com, LKML <linux-kernel@...r.kernel.org>, 
	linux-serial@...r.kernel.org, linux- stable <stable@...r.kernel.org>
Subject: Re: [PATCH v2] serial: 8250: always disable IRQ during THRE test

On Thu, Oct 16, 2025 at 3:05 PM Peng Zhang <zhangpeng.00@...edance.com> wrote:
>
> commit 039d4926379b ("serial: 8250: Toggle IER bits on only after irq
> has been set up") moved IRQ setup before the THRE test, so 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.
>
> Cc: stable@...r.kernel.org
> Fixes: 039d4926379b ("serial: 8250: Toggle IER bits on only after irq has been set up")
> Signed-off-by: Peng Zhang <zhangpeng.00@...edance.com>

Reviewed-by: Muchun Song <songmuchun@...edance.com>