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Date: Thu, 1 Aug 2013 17:28:38 +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
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.
>>>>>>>
>>>>>>> .
>>
>>
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