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

[wengang wang]

Sunil,

bugzilla filed with answers to your questions.
http://oss.oracle.com/bugzilla/show_bug.cgi?id=986

regards,
wengang.
Sunil Mushran wrote:
> Wengang,
>
> I needed some clarification. Is the fix proposed in kernel or in ocfs2,
> or in kernel and in ocfs2?
>
> Is the bug in 1.2/el4 only? Has 1.2/el5 or current mainline tested?
> Just want to know what has been tested.
>
> Also, please could you a file a bugzilla with the details. Especially
> the testcase. Will be useful as we will be able to test it in
> multiple envs.
>
> Thanks
> Sunil
>
> 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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>