On 11/26/2011 11:13 PM, Yongqiang Yang wrote:

Hi,

It can be tested by xfstests 61 or 91, I did not remember which one.

ok, I will try it later. But I still wonder how it happens. See my
comments below.

It can be reproduced by reading on a fallocted block and write the block
after the fallocted block.  Then the written block can not be written
out by da_writepages.

Why? in read no bh will be created, and in write only the written bh
will be mapped and set unwritten. How could that happen? Sorry, but this
explanation doesn't convince me.

Yongqiang.

On Saturday, November 26, 2011, Tao Ma <tm@tao.ma <mailto:tm@tao.ma>> wrote:

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Hi Yongqiang,
On 11/23/2011 05:15 PM, Yongqiang Yang wrote:

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If there is a unwritten but clean buffer in a page and there is a

dirty buffer

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after the buffer, then mpage_submit_io does not write the dirty

buffer out.

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As a result, da_writepages loops forever.

Did you ever meet with this bug or just find it to be a possible bug by
skimming the code? Actually, I can't find a proper way to get a buffer
which can satisfy the check.

Thanks
Tao

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This patch fixes the problem by checking dirty flag.

Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com

<mailto:xiaoqiangnk@gmail.com>>

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---
 fs/ext4/inode.c |    7 +++++--
 1 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 755f6c7..20a1d17 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c

@@ -1339,8 +1339,11 @@ static int mpage_da_submit_io(struct

mpage_da_data *mpd,

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                                      clear_buffer_unwritten(bh);
                              }

-                             /* skip page if block allocation undone */
-                             if (buffer_delay(bh) ||

buffer_unwritten(bh))

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+                             /*
+                              * skip page if block allocation undone and
+                              * block is dirty
+                              */
+                             if (ext4_bh_delay_or_unwritten(NULL, bh))
                                      skip_page = 1;
                              bh = bh->b_this_page;
                              block_start += bh->b_size;

-- 
Best Wishes
Yongqiang Yang