2018-08-16 18:16:07

by Larry Chen

Subject: [PATCH] fix crash on ocfs2_duplicate_clusters_by_page

ocfs2_duplicate_clusters_by_page may crash if an extent's page is dirty.
When a page has not been written back, it is still in dirty state. If at
that moment, ocfs2_duplicate_clusters_by_page is called against this
page, the crash happens.

To fix this bug, we can just unlock the page and wait the page until
it's not dirty.

I don't know whether the patch is appropriate, so I need comments,
thanks.

The following is the core dump:

kernel BUG at /root/code/ocfs2/refcounttree.c:2961!
__ocfs2_move_extent+0x80/0x450 [ocfs2]
? __ocfs2_claim_clusters+0x130/0x250 [ocfs2]
ocfs2_defrag_extent+0x5b8/0x5e0 [ocfs2]
__ocfs2_move_extents_range+0x2a4/0x470 [ocfs2]
ocfs2_move_extents+0x180/0x3b0 [ocfs2]
? ocfs2_wait_for_recovery+0x13/0x70 [ocfs2]
ocfs2_ioctl_move_extents+0x133/0x2d0 [ocfs2]
ocfs2_ioctl+0x253/0x640 [ocfs2]
do_vfs_ioctl+0x90/0x5f0
SyS_ioctl+0x74/0x80
do_syscall_64+0x74/0x140
entry_SYSCALL_64_after_hwframe+0x3d/0xa2

To: [email protected],
[email protected]
Cc: [email protected],
[email protected],
[email protected]

Signed-off-by: Larry Chen <[email protected]>
---
fs/ocfs2/refcounttree.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/fs/ocfs2/refcounttree.c b/fs/ocfs2/refcounttree.c
index 7869622af22a..ee3b9dbbc310 100644
--- a/fs/ocfs2/refcounttree.c
+++ b/fs/ocfs2/refcounttree.c
@@ -2946,6 +2946,7 @@ int ocfs2_duplicate_clusters_by_page(handle_t *handle,
if (map_end & (PAGE_SIZE - 1))
to = map_end & (PAGE_SIZE - 1);

+retry:
page = find_or_create_page(mapping, page_index, GFP_NOFS);
if (!page) {
ret = -ENOMEM;
@@ -2957,8 +2958,13 @@ int ocfs2_duplicate_clusters_by_page(handle_t *handle,
* In case PAGE_SIZE <= CLUSTER_SIZE, This page
* can't be dirtied before we CoW it out.
*/
- if (PAGE_SIZE <= OCFS2_SB(sb)->s_clustersize)
- BUG_ON(PageDirty(page));
+ if (PAGE_SIZE <= OCFS2_SB(sb)->s_clustersize) {
+ if (PageDirty(page)) {
+ unlock_page(page);
+ cond_resched();
+ goto retry;
+ }
+ }

if (!PageUptodate(page)) {
ret = block_read_full_page(page, ocfs2_get_block);
--
2.13.7

2018-08-20 09:33:49

by Gang He

Subject: Re: [Ocfs2-devel] [PATCH] fix crash on ocfs2_duplicate_clusters_by_page

Hello Larry,


>>> On 2018/8/16 at 19:24, in message <[email protected]>,
Larry Chen <[email protected]> wrote:
> ocfs2_duplicate_clusters_by_page may crash if an extent's page is dirty.
> When a page has not been written back, it is still in dirty state. If at
> that moment, ocfs2_duplicate_clusters_by_page is called against this
> page, the crash happens.
>
> To fix this bug, we can just unlock the page and wait the page until
> it's not dirty.
>
> I don't know whether the patch is appropriate, so I need comments,
> thanks.
>
> The following is the core dump:
>
> kernel BUG at /root/code/ocfs2/refcounttree.c:2961!
> __ocfs2_move_extent+0x80/0x450 [ocfs2]
> ? __ocfs2_claim_clusters+0x130/0x250 [ocfs2]
> ocfs2_defrag_extent+0x5b8/0x5e0 [ocfs2]
> __ocfs2_move_extents_range+0x2a4/0x470 [ocfs2]
> ocfs2_move_extents+0x180/0x3b0 [ocfs2]
> ? ocfs2_wait_for_recovery+0x13/0x70 [ocfs2]
> ocfs2_ioctl_move_extents+0x133/0x2d0 [ocfs2]
> ocfs2_ioctl+0x253/0x640 [ocfs2]
> do_vfs_ioctl+0x90/0x5f0
> SyS_ioctl+0x74/0x80
> do_syscall_64+0x74/0x140
> entry_SYSCALL_64_after_hwframe+0x3d/0xa2
>
> To: [email protected],
> [email protected]
> Cc: [email protected],
> [email protected],
> [email protected]
>
> Signed-off-by: Larry Chen <[email protected]>
> ---
> fs/ocfs2/refcounttree.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/fs/ocfs2/refcounttree.c b/fs/ocfs2/refcounttree.c
> index 7869622af22a..ee3b9dbbc310 100644
> --- a/fs/ocfs2/refcounttree.c
> +++ b/fs/ocfs2/refcounttree.c
> @@ -2946,6 +2946,7 @@ int ocfs2_duplicate_clusters_by_page(handle_t *handle,
> if (map_end & (PAGE_SIZE - 1))
> to = map_end & (PAGE_SIZE - 1);
>
> +retry:
> page = find_or_create_page(mapping, page_index, GFP_NOFS);
> if (!page) {
> ret = -ENOMEM;
> @@ -2957,8 +2958,13 @@ int ocfs2_duplicate_clusters_by_page(handle_t *handle,
> * In case PAGE_SIZE <= CLUSTER_SIZE, This page
> * can't be dirtied before we CoW it out.
> */
> - if (PAGE_SIZE <= OCFS2_SB(sb)->s_clustersize)
> - BUG_ON(PageDirty(page));
> + if (PAGE_SIZE <= OCFS2_SB(sb)->s_clustersize) {
> + if (PageDirty(page)) {
> + unlock_page(page);
Here, if we find this page is dirty, could we write this page to the disk initiatively? rather than wait for the page become clean by VM mechanism.

Thanks
Gang

> + cond_resched();
> + goto retry;
> + }
> + }
>
> if (!PageUptodate(page)) {
> ret = block_read_full_page(page, ocfs2_get_block);
> --
> 2.13.7
>
>
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