[Ocfs2-devel] [BUGFIX][OCFS2 1/1] inode truncating

[wengang wang]

/an ocfs2 bug:
a truncate races with ocfs2_get_block(...,0).

1) 'dd' is doing a truncate, clearing the page cache and reset inode size./
/2) between clearing page cache and resizing inode, a read comes and 
create a /
/new page and insert it to page cache./
/3) the read(from `cat`) set buffer head in the new page as mapped but 
doesn't increase /   /ip_mmu_private in ocfs2_get_block() because it's a 
read./
/4) a write from 'dd' matches the page that the read created. because 
the buffer /
  /heads are already mapped, it doesn't call ocfs2_get_block. the 
ip_mmu_private /
  /keeps unchanged since last write./
/5) in cont_prepare_write() it dead loops since bytes(ip_mmu_private) is 
not /
  /increased in last prepare write./

BUG is described in 
s://bug.oraclecorp.com/pls/bug/webbug_print.show?c_rptno=7183894.

solution:
/1) moves the clearing of page cache truncate_inode_pages() from 
ocfs2_truncate_file() to/
  /ocfs2_set_inode_size() after resizing inode size and i_blocks./
/2) in ocfs2_get_block(), add checks on iblock >= inode->i_blocks. if 
true, return -EIO.
3) //a kernel bug fix is needed for 2.6.9 kernel.
//see https://bugzilla.redhat.com/show_bug.cgi?id=453359/

 aops.c |    6 ++++++
 file.c |    4 ++--
 2 files changed, 8 insertions(+), 2 deletions(-)

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