From mboxrd@z Thu Jan 1 00:00:00 1970 From: Greg Kroah-Hartman Subject: Re: [PATCH] tty: Fix race condition if flushing tty flip buffers Date: Mon, 8 Apr 2013 11:48:04 -0700 Message-ID: <20130408184804.GA4066@kroah.com> References: <5149AFD0.8020604@izyk.ru> <1363800043-21449-1-git-send-email-peter@hurleysoftware.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail-pa0-f52.google.com ([209.85.220.52]:40558 "EHLO mail-pa0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S935047Ab3DHSsK (ORCPT ); Mon, 8 Apr 2013 14:48:10 -0400 Received: by mail-pa0-f52.google.com with SMTP id fb10so3402345pad.39 for ; Mon, 08 Apr 2013 11:48:08 -0700 (PDT) Content-Disposition: inline In-Reply-To: <1363800043-21449-1-git-send-email-peter@hurleysoftware.com> Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org To: Peter Hurley Cc: Ilya Zykov , Jiri Slaby , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org On Wed, Mar 20, 2013 at 01:20:43PM -0400, Peter Hurley wrote: > As Ilya Zykov identified in his patch 'PROBLEM: Race condition in > tty buffer's function flush_to_ldisc()', a race condition exists > which allows a parallel flush_to_ldisc() to flush and free the tty > flip buffers while those buffers are in-use. For example, > > CPU 0 | CPU 1 | CPU 2 > | flush_to_ldisc() | > | grab spin lock | > tty_buffer_flush() | | flush_to_ldisc() > wait for spin lock | | wait for spin lock > | if (!test_and_set_bit(TTYP_FLUSHING)) | > | while (next flip buffer) | > | ... | > | drop spin lock | > grab spin lock | | > if (test_bit(TTYP_FLUSHING)) | | > set_bit(TTYP_FLUSHPENDING) | receive_buf() | > drop spin lock | | > | | grab spin lock > | | if (!test_and_set_bit(TTYP_FLUSHING)) > | | if (test_bit(TTYP_FLUSHPENDING)) > | | __tty_buffer_flush() > > CPU 2 has just flushed and freed all tty flip buffers while CPU 1 is > transferring data from the head flip buffer. > > The original patch was rejected under the assumption that parallel > flush_to_ldisc() was not possible. Because of necessary changes to > the workqueue api, work items can execute in parallel on SMP. > > This patch differs slightly from the original patch by testing for > a pending flush _after_ each receive_buf(), since TTYP_FLUSHPENDING > can only be set while the lock is dropped around receive_buf(). > > Reported-by: Ilya Zykov > Signed-off-by: Peter Hurley > --- > drivers/tty/tty_buffer.c | 22 ++++++++++------------ > 1 file changed, 10 insertions(+), 12 deletions(-) What tree is this against? Does it need your other larger set of ldisc patches, or can it be applied without it? confused, greg k-h