From: Zhao Hongjiang Subject: Re: xfstests failure generic/239 Date: Thu, 1 Aug 2013 17:28:38 +0800 Message-ID: <51FA2A46.5020904@huawei.com> References: <51B2A15F.1060704@huawei.com> <20130608223038.GA19229@thunk.org> <51F732FA.9090307@huawei.com> <20130730154801.GA22013@quack.suse.cz> <51F8799D.7070202@huawei.com> <20130731141340.GB22930@quack.suse.cz> <51F9C254.1000207@huawei.com> <20130801084941.GB19219@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 szxga01-in.huawei.com ([119.145.14.64]:63595 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751909Ab3HAJ2t (ORCPT ); Thu, 1 Aug 2013 05:28:49 -0400 In-Reply-To: <20130801084941.GB19219@quack.suse.cz> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 2013/8/1 16:49, Jan Kara wrote: > Hi, > > On Thu 01-08-13 10:05:08, Zhao Hongjiang wrote: >> It hit this bug, the "Bug happened!" is come out everytime while the test >> is fail. Any suggestion for fix this? > OK, so the test is still failing after using io_end instead of > iocb->private? If yes, I'm not sure where the problem exactly is, sorry. > I hit the bug just with the follow code that you give out: if (io_end != NULL) { if (iocb->private == NULL) printk("Bug happened!\n"); EXT4_I(inode)->cur_aio_dio = NULL; } With this the "Bug happened!" is come out everytime while the test is fail. But if the test case is pass, the "Bug happened!" never come out! > >> On 2013/7/31 22:13, Jan Kara wrote: >>> 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. >>>>>>> >>>>>>> . >> >>