linux-ext4 - Re: DIO process stuck apparently due to dioread

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Message-ID: <4E455C72.4030907@redhat.com>
Date:	Fri, 12 Aug 2011 12:01:38 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Michael Tokarev <mjt@....msk.ru>
CC:	Jan Kara <jack@...e.cz>, Jiaying Zhang <jiayingz@...gle.com>,
	linux-ext4@...r.kernel.org
Subject: Re: DIO process stuck apparently due to dioread_nolock (3.0)

On 8/12/11 10:55 AM, Michael Tokarev wrote:
> 12.08.2011 17:07, Jan Kara wrote:
> []
>>>>> [   76.982985] EXT4-fs (dm-1): Unaligned AIO/DIO on inode 3407879 by oracle; performance will be poor.
>>>>> [ 1469.734114] SysRq : Show Blocked State
>>>>> [ 1469.734157]   task                        PC stack   pid father
>>>>> [ 1469.734473] oracle          D 0000000000000000     0  6146      1 0x00000000
>>>>> [ 1469.734525]  ffff88103f604810 0000000000000082 ffff881000000000 ffff881079791040
>>>>> [ 1469.734603]  ffff880432c19fd8 ffff880432c19fd8 ffff880432c19fd8 ffff88103f604810
>>>>> [ 1469.734681]  ffffea000ec13590 ffffffff00000000 ffff881438c8dad8 ffffffff810eeda2
>>>>> [ 1469.734760] Call Trace:
>>>>> [ 1469.734800]  [<ffffffff810eeda2>] ? __do_fault+0x422/0x520
>>>>> [ 1469.734863]  [<ffffffffa0123e6d>] ? ext4_file_write+0x20d/0x260 [ext4]
>>>>> [ 1469.734909]  [<ffffffff8106aee0>] ? abort_exclusive_wait+0xb0/0xb0
>>>>> [ 1469.734956]  [<ffffffffa0123c60>] ? ext4_llseek+0x120/0x120 [ext4]
>>>>> [ 1469.734999]  [<ffffffff81162173>] ? aio_rw_vect_retry+0x73/0x1d0
>>>>> [ 1469.735039]  [<ffffffff8116302f>] ? aio_run_iocb+0x5f/0x160
>>>>> [ 1469.735078]  [<ffffffff81164258>] ? do_io_submit+0x4f8/0x600
>>>>> [ 1469.735122]  [<ffffffff81359b52>] ? system_call_fastpath+0x16/0x1b
> []
>>   Probably not, just garbage on stack confuses the stack unwinder. Note
>> that e.g. ext4_llseek() is at the end of function as well as
>> abort_exclusive_wait() which probably means these functions have already
>> finished and just left their addresses on stack. Could you disasseble
>> your ext4_file_write() function and check where offset 0x20d is? Sadly you
>> won't see where calls are going when ext4 is compiled as a module (module
>> is linked when loaded into kernel) so it might be easier to compile ext4
>> into the kernel and disassemble the function in vmlinux file.
>>
>>> Btw, does ext4_llseek() look sane here?  Note it's called from
>>> aio_submit() -- does it _ever_ implement SEEKs?
>>>
>>> Maybe some debugging is neecessary here?
>>   Yes. The trouble is I'm not completely sure where we are hanging yet.
>> We should know more from your disassembly. But you can try running with
>> attached debug patch - maybe it shows something interesting.
> 
> With ext4 built-in and your patch applied:
> 
> [  429.061524] EXT4-fs (sda11): Unaligned AIO/DIO on inode 5767181 by oracle; performance will be poor.
> [  429.061669] Going to wait for 18446744073709551199 aios
> [  437.717942] SysRq : Show Blocked State
> [  437.718109]   task                        PC stack   pid father
> [  437.718528] oracle          D 0000000000000000     0  3844      1 0x00000000
> [  437.718767]  ffff88203e330080 0000000000000082 0000000000000000 ffff881078e3f7d0
> [  437.719156]  ffff88203dc15fd8 ffff88203dc15fd8 ffff88203dc15fd8 ffff88203e330080
> [  437.719546]  0000001e0000000f 0000000000000246 205b88103f806680 3136302e39323420
> [  437.719935] Call Trace:
> [  437.720043]  [<ffffffff8139b976>] ? printk+0x43/0x48
> [  437.720155]  [<ffffffff8118e16d>] ? ext4_file_write+0x21d/0x290
> [  437.720267]  [<ffffffff8106aee0>] ? abort_exclusive_wait+0xb0/0xb0
> [  437.720376]  [<ffffffff8118df50>] ? ext4_llseek+0x120/0x120
> [  437.720485]  [<ffffffff81162173>] ? aio_rw_vect_retry+0x73/0x1d0
> [  437.720593]  [<ffffffff8116302f>] ? aio_run_iocb+0x5f/0x160
> [  437.720699]  [<ffffffff81164258>] ? do_io_submit+0x4f8/0x600
> [  437.720811]  [<ffffffff813a3152>] ? system_call_fastpath+0x16/0x1b
> 
> Trying to find how to disassemble things now...
> And yes, 18446744073709551199 aios sounds quite alot ;)

looks like it went negative.

I see that in one case we set EXT4_IO_END_UNWRITTEN, but don't increment the counter.
We decrement the counter for every EXT4_IO_END_UNWRITTEN completion, I think.

I'm not quite sure if that was intentional or not, but it might be a place to start.
I haven't though hard about this, in the middle of something else right now,
but this looks like it's a probllem in my code from that unaligned AIO patch,
perhaps...

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 3e5191f..7366488 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3640,6 +3640,7 @@ static void ext4_end_io_buffer_write(struct buffer_head *bh, int uptodate)
 
        io_end->flag = EXT4_IO_END_UNWRITTEN;
        inode = io_end->inode;
+       atomic_inc(&EXT4_I(inode)->i_aiodio_unwritten);
 
        /* Add the io_end to per-inode completed io list*/
        spin_lock_irqsave(&EXT4_I(inode)->i_completed_io_lock, flags);


> Thanks,
> 
> /mjt
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