From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754773AbbBCWX2 (ORCPT ); Tue, 3 Feb 2015 17:23:28 -0500 Received: from ipmail05.adl6.internode.on.net ([150.101.137.143]:23111 "EHLO ipmail05.adl6.internode.on.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754011AbbBCWX1 (ORCPT ); Tue, 3 Feb 2015 17:23:27 -0500 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: A2DqFgCjSdFUPJVzLHlagwaBK4Iyg3msFQEBAQEBAQaYKQICAQECgRREAQEBAQEGAQEBATg7hAwBAQEDAScTHCMFCwgDFQMJJQ8FJQMHGhOIJQfXBgEBAQcCAR8YhWyJdAeEKQWYMYo4iCiCJByBZCoxgkIBAQE Date: Wed, 4 Feb 2015 09:23:12 +1100 From: Dave Chinner To: Linus Torvalds Cc: linux-aio@kvack.org, Kernel Mailing List , Benjamin LaHaise Subject: Re: [GIT PULL] aio: fix sleeping while TASK_INTERRUPTIBLE Message-ID: <20150203222312.GO6282@dastard> References: <20150201144058.GM2974@kvack.org> <20150201221458.GN2974@kvack.org> <20150202001628.GO2974@kvack.org> <20150202052944.GF4251@dastard> <20150202055429.GH4251@dastard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 02, 2015 at 10:45:42AM -0800, Linus Torvalds wrote: > On Sun, Feb 1, 2015 at 9:54 PM, Dave Chinner wrote: > > > > Simple enough - the patch below removes the warning from generic/036 > > for me. > > So because this is a debugging thing, I'd actually prefer these > "sched_annotate_sleep()" calls to always come with short comments in > code why they exist and why they are fine. Ok, I just copied the existing users which don't have any comments. > In this case, it might be as simple as > > "If the mutex blocks and wakes us up, the loop in > wait_event_interruptible_hrtimeout() will just schedule without > sleeping and repeat. The ting-lock doesn't block often enough for this > to be a performance issue". > > or perhaps just point to the comment in read_events(). Both. New patch below. -Dave. -- Dave Chinner david@fromorbit.com aio: annotate aio_read_event_ring for sleep patterns From: Dave Chinner Under CONFIG_DEBUG_ATOMIC_SLEEP=y, aio_read_event_ring() will throw warnings like the following due to being called from wait_event context: WARNING: CPU: 0 PID: 16006 at kernel/sched/core.c:7300 __might_sleep+0x7f/0x90() do not call blocking ops when !TASK_RUNNING; state=1 set at [] prepare_to_wait_event+0x63/0x110 Modules linked in: CPU: 0 PID: 16006 Comm: aio-dio-fcntl-r Not tainted 3.19.0-rc6-dgc+ #705 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 ffffffff821c0372 ffff88003c117cd8 ffffffff81daf2bd 000000000000d8d8 ffff88003c117d28 ffff88003c117d18 ffffffff8109beda ffff88003c117cf8 ffffffff821c115e 0000000000000061 0000000000000000 00007ffffe4aa300 Call Trace: [] dump_stack+0x4c/0x65 [] warn_slowpath_common+0x8a/0xc0 [] warn_slowpath_fmt+0x46/0x50 [] ? prepare_to_wait_event+0x63/0x110 [] ? prepare_to_wait_event+0x63/0x110 [] __might_sleep+0x7f/0x90 [] mutex_lock+0x24/0x45 [] aio_read_events+0x4c/0x290 [] read_events+0x1ec/0x220 [] ? prepare_to_wait_event+0x110/0x110 [] ? hrtimer_get_res+0x50/0x50 [] SyS_io_getevents+0x4d/0xb0 [] system_call_fastpath+0x12/0x17 ---[ end trace bde69eaf655a4fea ]--- There is not actually a bug here, so annotate the code to tell the debug logic that everything is just fine and not to fire a false positive. Signed-off-by: Dave Chinner --- V2: added comment to explain the annotation. fs/aio.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/fs/aio.c b/fs/aio.c index 1b7893e..327ef6d 100644 --- a/fs/aio.c +++ b/fs/aio.c @@ -1140,6 +1140,13 @@ static long aio_read_events_ring(struct kioctx *ctx, long ret = 0; int copy_ret; + /* + * The mutex can block and wake us up and that will cause + * wait_event_interruptible_hrtimeout() to schedule without sleeping + * and repeat. This should be rare enough that it doesn't cause + * peformance issues. See the comment in read_events() for more detail. + */ + sched_annotate_sleep(); mutex_lock(&ctx->ring_lock); /* Access to ->ring_pages here is protected by ctx->ring_lock. */