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Date: Thu, 1 Aug 2013 23:03:24 +0200
From: Jan Kara <jack@...e.cz>
To: Zhao Hongjiang <zhaohongjiang@...wei.com>
Cc: Jan Kara <jack@...e.cz>, Theodore Ts'o <tytso@....edu>,
linux-ext4@...r.kernel.org, hch@....de, khoroshilov@...ras.ru
Subject: Re: xfstests failure generic/239
On Thu 01-08-13 17:28:38, Zhao Hongjiang wrote:
> 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!
Yes, so we know early completion of direct IO triggers the bug. The above
condition fixes a bug in ext4_ext_direct_IO() but as you are still getting
test failures, there must be some other bug still present. And I don't know
where it is...
Honza
> >> 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.
> >>>>>>>
> >>>>>>> .
> >>
> >>
>
>
--
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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