From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793193748; b=BmFXFyTSNZqlb4bsplzrA/gfte7+Nt4xrXCNwhyVg1W12a96EQxt4DVnLOyR5uoha6/t GjEXeTmvlxfjoD/nOsK6991RGcKKwnoqUUdxfTivTWmQ0gziE39lVk1ozoO2pBtqOXI9g 9nQqR0GgAmxlZyx4fMSK/MpC+AGdvgY/rG8ckrDUYS7fRRZOpJTxp5Xm9q+xnqhotuY2h NRl5DNqSlK9deq76KRs08uAmGTKYYuV7dut3H1wwRrEixZPFkDBBoWNDzA9z7pzICHNY9 3pPKg9mbCEL5DTfuzhusfCyN6eVf1pkEbwGMkYZ8QfzGBHFeBQkGN5FHPzH1zaQpJNw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793193748; h=Received:DKIM-Signature:Received:From:To:Cc:Subject:Date:Message-ID: X-Mailer:In-Reply-To:References:MIME-Version: Content-Transfer-Encoding; bh=XOIpWApm+1y0y5e8wWUvnK4ebxNnpBPEyp9x+DwkePw=; b=ZRKC1Uh8KsNPO3By8kWX6qdajI0LIftFVt65uLB/mTW931fJBsOSVZKr2+0lnxyQClP3 iPt7Wv9IC/zoiXnmW+BtOf0rCPmfVbexU8nhqmvCwZ4lwfi3M/c0ipf4lagg5IFRisNOo HpmSMopXxiMgRN1X7HKwMPxmRh5w3YqwmsWeLrjUMJaupJgMu33si7KCCkSp9ivNk2IdD QaWLkRmMKESnz1bpj2jLW8Qium9mSTgDov+kW2xuF2QnEqIwxfiFRdnF620ByD39BmLIY 4OcJqvJW4dNy/uNSvs0JzCtF7QKfJwTJUCPyORKgMKhpGfddpaWnWV3piHBP+PbCrag== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=cr+nW6UM; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 07213606A31D; Wed, 28 Oct 2026 13:22:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=cr+nW6UM Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8ADD71F01828; Wed, 28 Oct 2026 13:22:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793193747; bh=XOIpWApm+1y0y5e8wWUvnK4ebxNnpBPEyp9x+DwkePw=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=cr+nW6UMQyT7j2NM5iRb6iyhZhxKCeyBRLSyY6k2LR2cLNslNqQ+ehBRPc8TX3hri RVIrIriDmrxkA/rhiegv4ozLswc4cgS9lqntczP1U6WPfE199YaG3GgbrkMXvpM2YP mhCTMHwc98lFFifeHpn4fXn4nzaLi24ATnjHY3ZqibN+maj5+QCBXpQF9eLp0YB/Rz Gu+1PEH4tUbaB8IegPJ4pxi1evVluNDAdtdyjZ/bOlpLVHItkKk1PWhDBDYt9qSkcd ro/tQIfjjNXUo1Db7O1mxEnPv73DD9N7hV7WJxroSnxGHUCeG28O5hi80CruOn82qW IB1/v46wk3OCQ== Received: from johan by xi.lan with local (Exim 4.99.5) (envelope-from ) id 1xM3bl-000000033X9-2bWx; Wed, 28 Oct 2026 14:22:25 +0100 From: Johan Hovold To: Greg Kroah-Hartman , Jiri Slaby Cc: linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, Johan Hovold , stable@vger.kernel.org Subject: [PATCH 2/3] tty: n_hdlc: fix read() hangup race Date: Wed, 28 Oct 2026 14:20:48 +0100 Message-ID: <20261028132049.728457-3-johan@kernel.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20261028132049.728457-1-johan@kernel.org> References: <20261028132049.728457-1-johan@kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Make sure to set the task state before checking the break conditions in the read() wait loop to avoid missing a racing wakeup. Note that before commit c96cf923a98d ("tty: Don't block on IO when ldisc change is pending") a racing task hanging up the tty could get stuck in uninterruptible sleep when there are blocked readers, but since then read() incorrectly returns -EAGAIN instead. The false-positive stuck hangup issue was flagged by an LLM. Fixes: 1035b63d3c6f ("n_hdlc: fix read and write locking") Cc: stable@vger.kernel.org # 2.6.38 Signed-off-by: Johan Hovold --- drivers/tty/n_hdlc.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/tty/n_hdlc.c b/drivers/tty/n_hdlc.c index 0fbc44968a44..02676ae9b112 100644 --- a/drivers/tty/n_hdlc.c +++ b/drivers/tty/n_hdlc.c @@ -431,6 +431,8 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file, add_wait_queue(&tty->read_wait, &wait); for (;;) { + set_current_state(TASK_INTERRUPTIBLE); + if (test_bit(TTY_OTHER_CLOSED, &tty->flags)) { ret = -EIO; break; @@ -438,8 +440,6 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file, if (tty_hung_up_p(file)) break; - set_current_state(TASK_INTERRUPTIBLE); - rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list); if (rbuf) break; -- 2.55.0