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Message-ID: <51F9C254.1000207@huawei.com> Date: Thu, 1 Aug 2013 10:05:08 +0800 From: Zhao Hongjiang <zhaohongjiang@...wei.com> To: Jan Kara <jack@...e.cz> CC: "Theodore Ts'o" <tytso@....edu>, <linux-ext4@...r.kernel.org>, <hch@....de>, <khoroshilov@...ras.ru> Subject: Re: xfstests failure generic/239 Hi, Jan It hit this bug, the "Bug happened!" is come out everytime while the test is fail. Any suggestion for fix this? Regards, Zhao 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. >>>>> >>>>> . -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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