From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752765AbaEBPSe (ORCPT ); Fri, 2 May 2014 11:18:34 -0400 Received: from mailout02.c08.mtsvc.net ([205.186.168.190]:35026 "EHLO mailout02.c08.mtsvc.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752194AbaEBPSc (ORCPT ); Fri, 2 May 2014 11:18:32 -0400 From: Peter Hurley To: Greg Kroah-Hartman Cc: Jiri Slaby , One Thousand Gnomes , Manfred Schlaegl , linux-kernel@vger.kernel.org, Peter Hurley Subject: [PATCH 1/2] Revert "tty: Fix race condition between __tty_buffer_request_room and flush_to_ldisc" Date: Fri, 2 May 2014 10:56:11 -0400 Message-Id: <1399042572-6533-1-git-send-email-peter@hurleysoftware.com> X-Mailer: git-send-email 1.8.1.2 X-Authenticated-User: 125194 peter@hurleysoftware.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This reverts commit 6a20dbd6caa2358716136144bf524331d70b1e03. Although the commit correctly identifies an unsafe race condition between __tty_buffer_request_room() and flush_to_ldisc(), the commit fixes the race with an unnecessary spinlock in a lockless algorithm. The follow-on commit, "tty: Fix lockless tty buffer race" fixes the race locklessly. Signed-off-by: Peter Hurley --- drivers/tty/tty_buffer.c | 16 ++-------------- include/linux/tty.h | 1 - 2 files changed, 2 insertions(+), 15 deletions(-) diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c index f1d30f6..8ebd9f8 100644 --- a/drivers/tty/tty_buffer.c +++ b/drivers/tty/tty_buffer.c @@ -255,16 +255,11 @@ static int __tty_buffer_request_room(struct tty_port *port, size_t size, if (change || left < size) { /* This is the slow path - looking for new buffers to use */ if ((n = tty_buffer_alloc(port, size)) != NULL) { - unsigned long iflags; - n->flags = flags; buf->tail = n; - - spin_lock_irqsave(&buf->flush_lock, iflags); b->commit = b->used; + smp_mb(); b->next = n; - spin_unlock_irqrestore(&buf->flush_lock, iflags); - } else if (change) size = 0; else @@ -448,7 +443,6 @@ static void flush_to_ldisc(struct work_struct *work) mutex_lock(&buf->lock); while (1) { - unsigned long flags; struct tty_buffer *head = buf->head; int count; @@ -456,19 +450,14 @@ static void flush_to_ldisc(struct work_struct *work) if (atomic_read(&buf->priority)) break; - spin_lock_irqsave(&buf->flush_lock, flags); count = head->commit - head->read; if (!count) { - if (head->next == NULL) { - spin_unlock_irqrestore(&buf->flush_lock, flags); + if (head->next == NULL) break; - } buf->head = head->next; - spin_unlock_irqrestore(&buf->flush_lock, flags); tty_buffer_free(port, head); continue; } - spin_unlock_irqrestore(&buf->flush_lock, flags); count = receive_buf(tty, head, count); if (!count) @@ -523,7 +512,6 @@ void tty_buffer_init(struct tty_port *port) struct tty_bufhead *buf = &port->buf; mutex_init(&buf->lock); - spin_lock_init(&buf->flush_lock); tty_buffer_reset(&buf->sentinel, 0); buf->head = &buf->sentinel; buf->tail = &buf->sentinel; diff --git a/include/linux/tty.h b/include/linux/tty.h index 036cccd..1c3316a 100644 --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -61,7 +61,6 @@ struct tty_bufhead { struct tty_buffer *head; /* Queue head */ struct work_struct work; struct mutex lock; - spinlock_t flush_lock; atomic_t priority; struct tty_buffer sentinel; struct llist_head free; /* Free queue head */ -- 1.8.1.2