From: Jan Kara Subject: Re: xfstests failure generic/239 Date: Wed, 31 Jul 2013 16:13:40 +0200 Message-ID: <20130731141340.GB22930@quack.suse.cz> References: <51B2A15F.1060704@huawei.com> <20130608223038.GA19229@thunk.org> <51F732FA.9090307@huawei.com> <20130730154801.GA22013@quack.suse.cz> <51F8799D.7070202@huawei.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Jan Kara , Theodore Ts'o , linux-ext4@vger.kernel.org, hch@lst.de, khoroshilov@ispras.ru To: Zhao Hongjiang Return-path: Received: from cantor2.suse.de ([195.135.220.15]:38632 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756400Ab3GaONm (ORCPT ); Wed, 31 Jul 2013 10:13:42 -0400 Content-Disposition: inline In-Reply-To: <51F8799D.7070202@huawei.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Wed 31-07-13 10:42:37, Zhao Hongjiang wrote: > On 2013/7/30 23:48, Jan Kara wrote: > > On Tue 30-07-13 11:28:58, Zhao Hongjiang wrote: > >> Hi, jack > >> > >> I test the latest kernel 3.11-rc2 and it seems the problem is fix by the > >> follow patch: commit id:97a851ed71cd9cc2542955e92a001c6ea3d21d35 (ext4: > >> use io_end for multiple bios). But it's so difficult to backport to > >> kernel 3.4-stable, any suggestion for this? > > Backporting that patch to stable kernels is no-go. It is far to intrusive > > for stable kernels. I was looking for a while how that patch could fix the > > problem you were observing. I think there is a subtle race possible when > > AIO DIO write completes before __blockdev_direct_IO() returns. In that case > > we set iocb->private to NULL in ext4_end_io_dio() but we also key off > > iocb->private in ext4_ext_direct_IO() as: > > if (iocb->private) > > ext4_inode_aio_set(inode, NULL); > > > > So in the case above we forget to reset inode's AIO pointer. That can then > > cause strange effects with unwritten extent handling (although I admit I'm > > not sure whether it can also cause the failure you observe) and > > 97a851ed71cd9cc2542955e92a001c6ea3d21d35 actually fixes that bug. You can > > easily check whether you are hitting that bug or not by changing the above > > condition from testing iocb->private to testing some private variable... > > E.g. you could declare io_end and set it to NULL one level up in > > ext4_ext_direct_IO() and then test io_end != NULL in that condition. > > > Thanks for your reply first. > I change the code like the follow: > > @@ -2921,6 +2921,7 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb, > struct inode *inode = file->f_mapping->host; > ssize_t ret; > size_t count = iov_length(iov, nr_segs); > + ext4_io_end_t *io_end = NULL; > > loff_t final_size = offset + count; > if (rw == WRITE && final_size <= inode->i_size) { > @@ -2947,8 +2948,7 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb, > iocb->private = NULL; > EXT4_I(inode)->cur_aio_dio = NULL; > if (!is_sync_kiocb(iocb)) { > - ext4_io_end_t *io_end = > - ext4_init_io_end(inode, GFP_NOFS); > + io_end = ext4_init_io_end(inode, GFP_NOFS); > if (!io_end) > return -ENOMEM; > io_end->flag |= EXT4_IO_END_DIRECT; > @@ -2970,8 +2970,10 @@ static ssize_t ext4_ext_direct_IO(int rw, struct kiocb *iocb, > ext4_end_io_dio, > NULL, > DIO_LOCKING); > - if (iocb->private) > + if (io_end != NULL) { > + printk("Zhao Hongjiang Ext4 test!\n"); > EXT4_I(inode)->cur_aio_dio = NULL; > + } > /* > * The io_end structure takes a reference to the inode, > * that structure needs to be destroyed and the > > And the print come out when i run the test everytime. So i think the test > hit the bug that you mentioned, Am i right or miss something? It is not a bug that you hit the branch with printk(). It would be a bug if the debug check looked like: if (io_end != NULL) { if (iocb->private == NULL) printk("Bug happened!\n"); EXT4_I(inode)->cur_aio_dio = NULL; } Honza > >> On 2013/6/9 6:30, Theodore Ts'o wrote: > >>> On Sat, Jun 08, 2013 at 11:13:35AM +0800, Zhao Hongjiang wrote: > >>>> > >>>> I run xfstests #239 against mainline 3.10.0-rc3, unfortunately it failure in my QEMU. I run the > >>>> case a hundred times, it certainly hit the failure several times. The failure msg is as follow: > >>>> > >>>> FSTYP -- ext4 > >>>> PLATFORM -- Linux/x86_64 3.10.0-rc3-mainline > >>>> > >>>> generic/239 1s ... - output mismatch (see /home/zhj/xfstests/results/generic/239.out.bad) > >>>> --- tests/generic/239.out 2013-06-07 22:04:09.000000000 -0400 > >>>> +++ /home/zff/xfstests/results/generic/239.out.bad 2013-06-07 22:04:09.000000000 -0400 > >>>> @@ -1,2 +1,515 @@ > >>>> QA output created by 239 > >>>> +hostname: Host name lookup failure > >>> > >>> OK, so this hostname failure is weird; I'm not sure what's causing > >>> this, but this I presume unrelated to the failure at hand. > >>> > >>>> Silence is golden > >>>> +0: 0x0 > >>>> +1: 0x0 > >>>> +2: 0x0 > >>>> +3: 0x0 > >>> > >>> This indicates a problem. Test generic/239 is running > >>> aio-dio-hole-filling-race.c, which submits an asynchronous, direct I/O > >>> 4k write with a buffer containing non-zero contents to a sparse file, > >>> and once the I/O has completed, it uses pread to read it back, using > >>> the same descriptor, so it is doing the read using direct I/O. It > >>> then checks to see if the read returns zero or not. > >>> > >>> The "XX: 0x0" lines indicates that buffer is zero, which implies that > >>> somehow aio_complete() is getting called before the uninitialized to > >>> initialized conversion is taking place. I'm not seeing how this is > >>> happening, though, so I'm a bit puzzled. If there are any unwritten > >>> extents, we don't call aio_complete() in ext4_end_io_dio(), but > >>> instead the conversion is queued via a call to ext4_add_compete_io(), > >>> and and aio_done() is only called on the iocb after the conversion is > >>> complete. > >>> > >>> Can anyone see something that I might be missing? > >>> > >>> - Ted > >>> > >>> P.S. Zhao, what was the hardware that you using to find this failure? > >>> I'm not seeing it, but then again if the failure is only happening > >>> once every few hundred runs that might explain it. I'm perhaps > >>> wondering if we should add a mode to aio-dio-hole-filling-race.c which > >>> allows it to try the race a large number of times, instead of just > >>> once. > >>> > >>> P.P.S. One thought.... perhaps it might be useful to have a debug > >>> mode where we use queue_delayed_work() to submit the conversion > >>> request to the workqueue. It will of course make certain workloads > >>> run slow as molasses, but it might expose some races so we can see > >>> them more easily. > >>> > >>> . > > > -- Jan Kara SUSE Labs, CR