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

[wengang wang <wen.gang.wang@oracle.com>]

This patch is based on 1.2 svn,
since there is no ip_mmu_private used in mainline, so maybe there is no 
such dead loop problem for mainline(not tested).

thanks
wengang.

wengang wang wrote:
> /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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