Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936010AbXHHPZv (ORCPT ); Wed, 8 Aug 2007 11:25:51 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S935724AbXHHPZG (ORCPT ); Wed, 8 Aug 2007 11:25:06 -0400 Received: from outpipe-village-512-1.bc.nu ([81.2.110.250]:50808 "EHLO the-village.bc.nu" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S935615AbXHHPZD (ORCPT ); Wed, 8 Aug 2007 11:25:03 -0400 Date: Wed, 8 Aug 2007 16:32:17 +0100 From: Alan Cox To: Alan Cox Cc: Paul Fulghum , Laurent Pinchart , linux-kernel@vger.kernel.org Subject: Re: Serial buffer memory leak Message-ID: <20070808163217.2f59fe84@the-village.bc.nu> In-Reply-To: <20070808161606.32a40793@the-village.bc.nu> References: <200708081158.06843.laurentp@cse-semaphore.com> <20070808144532.5e3a1998@the-village.bc.nu> <1186582307.3394.3.camel@x2.microgate.com> <200708081628.36897.laurentp@cse-semaphore.com> <1186584775.3508.13.camel@x2.microgate.com> <20070808161606.32a40793@the-village.bc.nu> X-Mailer: Claws Mail 2.9.1 (GTK+ 2.10.13; i386-redhat-linux-gnu) Organization: Red Hat UK Cyf., Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SL4 1TE, Y Deyrnas Gyfunol. Cofrestrwyd yng Nghymru a Lloegr o'r rhif cofrestru 3798903 Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4604 Lines: 134 On Wed, 8 Aug 2007 16:16:06 +0100 Alan Cox wrote: > > tty_buffer_flush() needs to wait for buf.flushpending to clear. > Should probably make the flushpending an atomic bit op to avoid taking > and retaking the lock. Ok try this for size folks. Use tty->flags bits for the flush status. Wait for the flag to clear again before returning Fix the doc error noted Fix flush of empty queue leaving stale flushpending Signed-off-by: Alan Cox diff -u --new-file --recursive --exclude-from /usr/src/exclude linux.vanilla-2.6.23rc1-mm1/drivers/char/tty_io.c linux-2.6.23rc1-mm1/drivers/char/tty_io.c --- linux.vanilla-2.6.23rc1-mm1/drivers/char/tty_io.c 2007-07-26 15:02:57.000000000 +0100 +++ linux-2.6.23rc1-mm1/drivers/char/tty_io.c 2007-08-08 16:01:36.843558336 +0100 @@ -369,25 +369,54 @@ } /** - * tty_buffer_flush - flush full tty buffers + * __tty_buffer_flush - flush full tty buffers * @tty: tty to flush * - * flush all the buffers containing receive data + * flush all the buffers containing receive data. Caller must + * hold the buffer lock and must have ensured no parallel flush to + * ldisc is running. * - * Locking: none + * Locking: Caller must hold tty->buf.lock */ -static void tty_buffer_flush(struct tty_struct *tty) +static void __tty_buffer_flush(struct tty_struct *tty) { struct tty_buffer *thead; - unsigned long flags; - spin_lock_irqsave(&tty->buf.lock, flags); while((thead = tty->buf.head) != NULL) { tty->buf.head = thead->next; tty_buffer_free(tty, thead); } tty->buf.tail = NULL; +} + +/** + * tty_buffer_flush - flush full tty buffers + * @tty: tty to flush + * + * flush all the buffers containing receive data. If the buffer is + * being processed by flush_to_ldisc then we defer the processing + * to that function + * + * Locking: none + */ + +static void tty_buffer_flush(struct tty_struct *tty) +{ + unsigned long flags; + spin_lock_irqsave(&tty->buf.lock, flags); + + /* If the data is being pushed to the tty layer then we can't + process it here. Instead set a flag and the flush_to_ldisc + path will process the flush request before it exits */ + if (test_bit(TTY_FLUSHING, &tty->flags)) { + set_bit(TTY_FLUSHPENDING, &tty->flags); + spin_unlock_irqrestore(&tty->buf.lock, flags); + wait_event(tty->read_wait, test_bit(TTY_FLUSHPENDING, &tty->flags) == 0); + return; + } + else + __tty_buffer_flush(tty); spin_unlock_irqrestore(&tty->buf.lock, flags); } @@ -3594,6 +3622,7 @@ return; spin_lock_irqsave(&tty->buf.lock, flags); + set_bit(TTY_FLUSHING, &tty->flags); /* So we know a flush is running */ head = tty->buf.head; if (head != NULL) { tty->buf.head = NULL; @@ -3607,6 +3636,11 @@ tty_buffer_free(tty, tbuf); continue; } + /* Ldisc or user is trying to flush the buffers + we are feeding to the ldisc, stop feeding the + line discipline as we want to empty the queue */ + if (test_bit(TTY_FLUSHPENDING, &tty->flags)) + break; if (!tty->receive_room) { schedule_delayed_work(&tty->buf.work, 1); break; @@ -3620,8 +3654,16 @@ disc->receive_buf(tty, char_buf, flag_buf, count); spin_lock_irqsave(&tty->buf.lock, flags); } + /* Restore the queue head */ tty->buf.head = head; } + /* We may have a deferred request to flush the input buffer, + if so pull the chain under the lock and empty the queue */ + if (test_bit(TTY_FLUSHPENDING, &tty->flags)) { + __tty_buffer_flush(tty); + clear_bit(TTY_FLUSHPENDING, &tty->flags); + } + clear_bit(TTY_FLUSHING, &tty->flags); spin_unlock_irqrestore(&tty->buf.lock, flags); tty_ldisc_deref(disc); diff -u --new-file --recursive --exclude-from /usr/src/exclude linux.vanilla-2.6.23rc1-mm1/include/linux/tty.h linux-2.6.23rc1-mm1/include/linux/tty.h --- linux.vanilla-2.6.23rc1-mm1/include/linux/tty.h 2007-07-26 15:02:04.000000000 +0100 +++ linux-2.6.23rc1-mm1/include/linux/tty.h 2007-08-08 16:00:28.089010616 +0100 @@ -274,6 +262,8 @@ #define TTY_PTY_LOCK 16 /* pty private */ #define TTY_NO_WRITE_SPLIT 17 /* Preserve write boundaries to driver */ #define TTY_HUPPED 18 /* Post driver->hangup() */ +#define TTY_FLUSHING 19 /* Flushing to ldisc in progress */ +#define TTY_FLUSHPENDING 20 /* Queued buffer flush pending */ #define TTY_WRITE_FLUSH(tty) tty_write_flush((tty)) - 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/