From: Zhao Hongjiang Subject: Re: xfstests failure generic/239 Date: Wed, 31 Jul 2013 10:42:37 +0800 Message-ID: <51F8799D.7070202@huawei.com> References: <51B2A15F.1060704@huawei.com> <20130608223038.GA19229@thunk.org> <51F732FA.9090307@huawei.com> <20130730154801.GA22013@quack.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Cc: "Theodore Ts'o" , , , To: Jan Kara Return-path: Received: from szxga02-in.huawei.com ([119.145.14.65]:20429 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751494Ab3GaCmp (ORCPT ); Tue, 30 Jul 2013 22:42:45 -0400 In-Reply-To: <20130730154801.GA22013@quack.suse.cz> Sender: linux-ext4-owner@vger.kernel.org List-ID: 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? Regards, Zhao >> 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. >>> >>> .