From owner-dev-commits-src-all@freebsd.org Wed Mar 10 15:06:17 2021 Return-Path: Delivered-To: dev-commits-src-all@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 6B1C656B946; Wed, 10 Mar 2021 15:06:17 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from mxrelay.nyi.freebsd.org (mxrelay.nyi.freebsd.org [IPv6:2610:1c1:1:606c::19:3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "mxrelay.nyi.freebsd.org", Issuer "R3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 4Dwb4n2brvz3hYB; Wed, 10 Mar 2021 15:06:17 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from gitrepo.freebsd.org (gitrepo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:5]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by mxrelay.nyi.freebsd.org (Postfix) with ESMTPS id 4BE9B11647; Wed, 10 Mar 2021 15:06:17 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from gitrepo.freebsd.org ([127.0.1.44]) by gitrepo.freebsd.org (8.16.1/8.16.1) with ESMTP id 12AF6Hkb050419; Wed, 10 Mar 2021 15:06:17 GMT (envelope-from git@gitrepo.freebsd.org) Received: (from git@localhost) by gitrepo.freebsd.org (8.16.1/8.16.1/Submit) id 12AF6Hmd050418; Wed, 10 Mar 2021 15:06:17 GMT (envelope-from git) Date: Wed, 10 Mar 2021 15:06:17 GMT Message-Id: <202103101506.12AF6Hmd050418@gitrepo.freebsd.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org From: Mitchell Horne Subject: git: 7e7f7beee732 - main - ns8250: don't drop IER_TXRDY on bus_grab/ungrab MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Git-Committer: mhorne X-Git-Repository: src X-Git-Refname: refs/heads/main X-Git-Reftype: branch X-Git-Commit: 7e7f7beee732810d3afcc83828341ac3e139b5bd Auto-Submitted: auto-generated X-BeenThere: dev-commits-src-all@freebsd.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: Commit messages for all branches of the src repository List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 10 Mar 2021 15:06:17 -0000 The branch main has been updated by mhorne: URL: https://cgit.FreeBSD.org/src/commit/?id=7e7f7beee732810d3afcc83828341ac3e139b5bd commit 7e7f7beee732810d3afcc83828341ac3e139b5bd Author: Mitchell Horne AuthorDate: 2021-03-10 14:57:12 +0000 Commit: Mitchell Horne CommitDate: 2021-03-10 15:04:42 +0000 ns8250: don't drop IER_TXRDY on bus_grab/ungrab It has been observed that some systems are often unable to resume from ddb after entering with debug.kdb.enter=1. Checking the status further shows the terminal is blocked waiting in tty_drain(), but it never makes progress in clearing the output queue, because sc->sc_txbusy is high. I noticed that when entering polling mode for the debugger, IER_TXRDY is set in the failure case. Since this bit is never tracked by the softc, it will not be restored by ns8250_bus_ungrab(). This creates a race in which a TX interrupt can be lost, creating the hang described above. Ensuring that this bit is restored is enough to prevent this, and resume from ddb as expected. The solution is to track this bit in the sc->ier field, for the same lifetime that TX interrupts are enabled. PR: 223917, 240122 Reviewed by: imp, manu Tested by: bz MFC after: 5 days Sponsored by: The FreeBSD Foundation Differential Revision: https://reviews.freebsd.org/D29130 --- sys/dev/uart/uart_dev_ns8250.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/sys/dev/uart/uart_dev_ns8250.c b/sys/dev/uart/uart_dev_ns8250.c index d920a76ae275..45b4d315c3d5 100644 --- a/sys/dev/uart/uart_dev_ns8250.c +++ b/sys/dev/uart/uart_dev_ns8250.c @@ -738,6 +738,7 @@ ns8250_bus_ipend(struct uart_softc *sc) } else { if (iir & IIR_TXRDY) { ipend |= SER_INT_TXIDLE; + ns8250->ier &= ~IER_ETXRDY; uart_setreg(bas, REG_IER, ns8250->ier); uart_barrier(bas); } else @@ -1035,7 +1036,9 @@ ns8250_bus_transmit(struct uart_softc *sc) uart_setreg(bas, REG_DATA, sc->sc_txbuf[i]); uart_barrier(bas); } - uart_setreg(bas, REG_IER, ns8250->ier | IER_ETXRDY); + if (!broken_txfifo) + ns8250->ier |= IER_ETXRDY; + uart_setreg(bas, REG_IER, ns8250->ier); uart_barrier(bas); if (broken_txfifo) ns8250_drain(bas, UART_DRAIN_TRANSMITTER);