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Date: Wed, 31 Jul 2013 10:42:37 +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 2013/7/30 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.
>>>
>>> .
--
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