inode truncating

/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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/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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Ocfs2-devel at oss.oracle.com
http://oss.oracle.com/mailman/listinfo/ocfs2-devel

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

Quoted 42 lines · 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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Ocfs2-devel mailing list
Ocfs2-devel at oss.oracle.com
http://oss.oracle.com/mailman/listinfo/ocfs2-devel