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Sat, 19 Sep 2026 12:24:01 -0700 (PDT) Received: from fedora ([202.47.63.86]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49fcd0f7e05sm100096265e9.4.2026.09.19.12.23.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 19 Sep 2026 12:24:00 -0700 (PDT) From: Muhammad Bilal To: gregkh@linuxfoundation.org Cc: jirislaby@kernel.org, fseidel@suse.de, linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, Muhammad Bilal Subject: [PATCH] tty: nozomi: lock tty_icount reads against the IRQ update path Date: Sun, 20 Sep 2026 00:23:49 +0500 Message-ID: <20260919192349.272409-1-meatuni001@gmail.com> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit receive_flow_control() updates port->tty_icount.{cts,dsr,rng,dcd} while interrupt_handler() holds dc->spin_mutex, but ntty_tiocgicount() and the TIOCMIWAIT snapshot/compare loop in ntty_ioctl()/ ntty_cflags_changed() read the same multi-field struct with no lock at all. A concurrent update can be observed mid-copy, and KCSAN flags the unlocked access. Add ntty_get_icount() to snapshot port->tty_icount under dc->spin_mutex and use it at all three read sites, matching the lock already used on the update side. Fixes: 20fd1e3bea55 ("nozomi driver") Signed-off-by: Muhammad Bilal --- drivers/tty/nozomi.c | 19 ++++++++++++++++--- 1 file changed, 16 insertions(+), 3 deletions(-) diff --git a/drivers/tty/nozomi.c b/drivers/tty/nozomi.c index ed99dbc9f990..4b2e224c0aa2 100644 --- a/drivers/tty/nozomi.c +++ b/drivers/tty/nozomi.c @@ -1671,10 +1671,23 @@ static int ntty_tiocmset(struct tty_struct *tty, return 0; } +static struct async_icount ntty_get_icount(struct port *port) +{ + struct nozomi *dc = port->dc; + struct async_icount cnow; + unsigned long flags; + + spin_lock_irqsave(&dc->spin_mutex, flags); + cnow = port->tty_icount; + spin_unlock_irqrestore(&dc->spin_mutex, flags); + + return cnow; +} + static int ntty_cflags_changed(struct port *port, unsigned long flags, struct async_icount *cprev) { - const struct async_icount cnow = port->tty_icount; + const struct async_icount cnow = ntty_get_icount(port); int ret; ret = ((flags & TIOCM_RNG) && (cnow.rng != cprev->rng)) @@ -1691,7 +1704,7 @@ static int ntty_tiocgicount(struct tty_struct *tty, struct serial_icounter_struct *icount) { struct port *port = tty->driver_data; - const struct async_icount cnow = port->tty_icount; + const struct async_icount cnow = ntty_get_icount(port); icount->cts = cnow.cts; icount->dsr = cnow.dsr; @@ -1715,7 +1728,7 @@ static int ntty_ioctl(struct tty_struct *tty, switch (cmd) { case TIOCMIWAIT: { - struct async_icount cprev = port->tty_icount; + struct async_icount cprev = ntty_get_icount(port); rval = wait_event_interruptible(port->tty_wait, ntty_cflags_changed(port, arg, &cprev)); -- 2.55.0