Path: csiph.com!eternal-september.org!feeder.eternal-september.org!aioe.org!bofh.it!news.nic.it!robomod From: Peter Hurley Newsgroups: linux.kernel Subject: [PATCH 1/7] tty: Remove tty_wait_until_sent_from_close() Date: Sat, 10 Oct 2015 22:10:02 +0200 Message-ID: References: X-Original-To: Greg Kroah-Hartman X-Google-Dkim-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=2bqDInDau0vqL6qHi4PwtUqVK5gbfc2Ja7sDYBDa7fM=; b=JP2pMzmk/nFzijhkdKhx64MZx5MtPpnOU75BWE+0GHSyky9rRG7Gn/nV87+Dc4dw0K cONrnRlbcZzgy4k8GyLxbC+7FNt5MFYvDNJc0wb8W7V0uuSFxasOelGHPxkEyCJIX7ZH EHXz9NQXRUl1svyFnapmBLq3eOhUsteM3MzpReU2qQJ7a1Jd8HDO3nxMkQkL/aUNtAk0 ljEaJ2fZtPOz+nJcjnNkdqsGzxcEOkJxq2oFe2b1XsC7QVVYR7lZUBtkLBziGKYLrekz N/WKHLm/FgNs3QmWCgHvwmfUQf1Y7t8mE8QFfAeWANXiT9EDW6IRAgZDtn4v08sKwfUG MQ4g== X-Gm-Message-State: ALoCoQnIMyz6vjSyqbFSluceOPA4GSlYu0BwJ7g9LzhdQ6D+HiiU7tjgiJJ9/R2PjpFBOy12rj9Q X-Received: by 10.140.98.54 with SMTP id n51mr22813420qge.75.1444507283350; Sat, 10 Oct 2015 13:01:23 -0700 (PDT) X-Mailer: git-send-email 2.6.1 Sender: robomod@news.nic.it List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Approved: robomod@news.nic.it Lines: 160 Organization: linux.* mail to news gateway X-Original-Cc: Jiri Slaby , Alan Cox , David Laight , Arnd Bergmann , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, netdev@vger.kernel.org, David Miller , Peter Hurley , Karsten Keil , linuxppc-dev@lists.ozlabs.org X-Original-Date: Sat, 10 Oct 2015 16:00:51 -0400 X-Original-Message-ID: <1444507257-7513-2-git-send-email-peter@hurleysoftware.com> X-Original-References: <1444507257-7513-1-git-send-email-peter@hurleysoftware.com> X-Original-Sender: linux-kernel-owner@vger.kernel.org Xref: csiph.com linux.kernel:1243998 tty_wait_until_sent_from_close() drops the tty lock while waiting for the tty driver to finish sending previously accepted data (ie., data remaining in its write buffer and transmit fifo). tty_wait_until_sent_from_close() was added by commit a57a7bf3fc7e ("TTY: define tty_wait_until_sent_from_close") to prevent the entire tty subsystem from being unable to open new ttys while waiting for one tty to close while output drained. However, since commit 0911261d4cb6 ("tty: Don't take tty_mutex for tty count changes"), holding a tty lock while closing does not prevent other ttys from being opened/closed/hung up, but only prevents lifetime event changes for the tty under lock. Holding the tty lock while waiting for output to drain does prevent parallel non-blocking opens (O_NONBLOCK) from advancing or returning while the tty lock is held. However, all parallel opens _already_ block even if the tty lock is dropped while closing and the parallel open advances. Blocking in open has been in mainline since at least 2.6.29 (see tty_port_block_til_ready(); note the test for O_NONBLOCK is _after_ the wait while ASYNC_CLOSING). IOW, before this patch a non-blocking open will sleep anyway for the _entire_ duration of a parallel hardware shutdown, and when it wakes, the error return will cause a release of its tty, and it will restart with a fresh attempt to open. Similarly with a blocking open that is already waiting; when it's woken, the hardware shutdown has already completed to ASYNC_INITIALIZED is not set, which forces a release and restart as well. So, holding the tty lock across the _entire_ close (which is what this patch does), even while waiting for output to drain, is equivalent to the current outcome wrt parallel opens. Cc: Alan Cox Cc: David Laight CC: Arnd Bergmann CC: Karsten Keil CC: linuxppc-dev@lists.ozlabs.org Signed-off-by: Peter Hurley --- drivers/isdn/i4l/isdn_tty.c | 2 +- drivers/tty/hvc/hvc_console.c | 2 +- drivers/tty/hvc/hvcs.c | 2 +- drivers/tty/tty_port.c | 11 ++--------- include/linux/tty.h | 18 ------------------ 5 files changed, 5 insertions(+), 30 deletions(-) diff --git a/drivers/isdn/i4l/isdn_tty.c b/drivers/isdn/i4l/isdn_tty.c index bc91261..2175225 100644 --- a/drivers/isdn/i4l/isdn_tty.c +++ b/drivers/isdn/i4l/isdn_tty.c @@ -1582,7 +1582,7 @@ isdn_tty_close(struct tty_struct *tty, struct file *filp) * line status register. */ if (port->flags & ASYNC_INITIALIZED) { - tty_wait_until_sent_from_close(tty, 3000); /* 30 seconds timeout */ + tty_wait_until_sent(tty, 3000); /* 30 seconds timeout */ /* * Before we drop DTR, make sure the UART transmitter * has completely drained; this is especially diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c index 9c30f67..e46d628 100644 --- a/drivers/tty/hvc/hvc_console.c +++ b/drivers/tty/hvc/hvc_console.c @@ -418,7 +418,7 @@ static void hvc_close(struct tty_struct *tty, struct file * filp) * there is no buffered data otherwise sleeps on a wait queue * waking periodically to check chars_in_buffer(). */ - tty_wait_until_sent_from_close(tty, HVC_CLOSE_WAIT); + tty_wait_until_sent(tty, HVC_CLOSE_WAIT); } else { if (hp->port.count < 0) printk(KERN_ERR "hvc_close %X: oops, count is %d\n", diff --git a/drivers/tty/hvc/hvcs.c b/drivers/tty/hvc/hvcs.c index f7ff97c..5997b17 100644 --- a/drivers/tty/hvc/hvcs.c +++ b/drivers/tty/hvc/hvcs.c @@ -1230,7 +1230,7 @@ static void hvcs_close(struct tty_struct *tty, struct file *filp) irq = hvcsd->vdev->irq; spin_unlock_irqrestore(&hvcsd->lock, flags); - tty_wait_until_sent_from_close(tty, HVCS_CLOSE_WAIT); + tty_wait_until_sent(tty, HVCS_CLOSE_WAIT); /* * This line is important because it tells hvcs_open that this diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c index 40b3183..d7d9f9c 100644 --- a/drivers/tty/tty_port.c +++ b/drivers/tty/tty_port.c @@ -463,10 +463,7 @@ static void tty_port_drain_delay(struct tty_port *port, struct tty_struct *tty) schedule_timeout_interruptible(timeout); } -/* Caller holds tty lock. - * NB: may drop and reacquire tty lock (in tty_wait_until_sent_from_close()) - * so tty and tty port may have changed state (but not hung up or reopened). - */ +/* Caller holds tty lock. */ int tty_port_close_start(struct tty_port *port, struct tty_struct *tty, struct file *filp) { @@ -502,7 +499,7 @@ int tty_port_close_start(struct tty_port *port, if (tty->flow_stopped) tty_driver_flush_buffer(tty); if (port->closing_wait != ASYNC_CLOSING_WAIT_NONE) - tty_wait_until_sent_from_close(tty, port->closing_wait); + tty_wait_until_sent(tty, port->closing_wait); if (port->drain_delay) tty_port_drain_delay(port, tty); } @@ -543,10 +540,6 @@ EXPORT_SYMBOL(tty_port_close_end); * tty_port_close * * Caller holds tty lock - * - * NB: may drop and reacquire tty lock (in tty_port_close_start()-> - * tty_wait_until_sent_from_close()) so tty and tty_port may have changed - * state (but not hung up or reopened). */ void tty_port_close(struct tty_port *port, struct tty_struct *tty, struct file *filp) diff --git a/include/linux/tty.h b/include/linux/tty.h index d072ded..614c822 100644 --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -657,24 +657,6 @@ extern void __lockfunc tty_lock_slave(struct tty_struct *tty); extern void __lockfunc tty_unlock_slave(struct tty_struct *tty); extern void tty_set_lock_subclass(struct tty_struct *tty); /* - * this shall be called only from where BTM is held (like close) - * - * We need this to ensure nobody waits for us to finish while we are waiting. - * Without this we were encountering system stalls. - * - * This should be indeed removed with BTM removal later. - * - * Locking: BTM required. Nobody is allowed to hold port->mutex. - */ -static inline void tty_wait_until_sent_from_close(struct tty_struct *tty, - long timeout) -{ - tty_unlock(tty); /* tty->ops->close holds the BTM, drop it while waiting */ - tty_wait_until_sent(tty, timeout); - tty_lock(tty); -} - -/* * wait_event_interruptible_tty -- wait for a condition with the tty lock held * * The condition we are waiting for might take a long time to -- 2.6.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/