From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932283AbWGLAOU (ORCPT ); Tue, 11 Jul 2006 20:14:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932284AbWGLAOU (ORCPT ); Tue, 11 Jul 2006 20:14:20 -0400 Received: from smtp.osdl.org ([65.172.181.4]:52162 "EHLO smtp.osdl.org") by vger.kernel.org with ESMTP id S932283AbWGLAOT (ORCPT ); Tue, 11 Jul 2006 20:14:19 -0400 Date: Tue, 11 Jul 2006 17:17:52 -0700 From: Andrew Morton To: "Serge E. Hallyn" Cc: hugh@veritas.com, serue@us.ibm.com, torvalds@osdl.org, linux-kernel@vger.kernel.org Subject: Re: please revert kthread from loop.c Message-Id: <20060711171752.4993903a.akpm@osdl.org> In-Reply-To: <20060711194932.GA27176@sergelap.austin.ibm.com> References: <20060627054612.GA15657@sergelap.austin.ibm.com> <20060711194932.GA27176@sergelap.austin.ibm.com> X-Mailer: Sylpheed version 1.0.0 (GTK+ 1.2.10; i386-vine-linux-gnu) 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 "Serge E. Hallyn" wrote: > > Convert loop.c from the deprecated kernel_thread to kthread. > I think you have a racelet here: > + } > spin_unlock_irq(&lo->lo_lock); > > - BUG_ON(!bio); > - loop_handle_bio(lo, bio); > - > - /* > - * upped both for pending work and tear-down, lo_pending > - * will hit zero then > - */ > - if (unlikely(!pending)) > - break; > + __set_current_state(TASK_INTERRUPTIBLE); > + schedule(); > } > > - complete(&lo->lo_done); > return 0; > } : if (kthread_should_stop()) { : spin_unlock_irq(&lo->lo_lock); : break; : } : spin_unlock_irq(&lo->lo_lock); : : __set_current_state(TASK_INTERRUPTIBLE); : schedule(); : If the wake_up_process() is delivered before the __set_current_state(), we'll miss the wakeup. If so, this should plug it. The same race is not possible against the loop_set_fd() wakeup because the thread isn't running at that stage, yes? diff -puN drivers/block/loop.c~kthread-convert-loopc-to-kthread-race-fix drivers/block/loop.c --- a/drivers/block/loop.c~kthread-convert-loopc-to-kthread-race-fix +++ a/drivers/block/loop.c @@ -525,8 +525,8 @@ static int loop_make_request(request_que goto out; lo->lo_pending++; loop_add_bio(lo, old_bio); - spin_unlock_irq(&lo->lo_lock); wake_up_process(lo->lo_thread); + spin_unlock_irq(&lo->lo_lock); return 0; out: @@ -600,9 +600,8 @@ static int loop_thread(void *data) spin_unlock_irq(&lo->lo_lock); break; } - spin_unlock_irq(&lo->lo_lock); - __set_current_state(TASK_INTERRUPTIBLE); + spin_unlock_irq(&lo->lo_lock); schedule(); } _