[Ocfs2-devel] [PATCH] ocfs2: __ocfs2_mknod_locked should return error when ocfs2_create_new_inode_locks() failed

[Joel Becker <jlbec@evilplan.org>]

On Wed, Mar 26, 2014 at 03:23:13PM +0800, Xue jiufei wrote:
> When ocfs2_create_new_inode_locks() return error, inode open lock may
> not be obtainted for this inode. So other nodes can remove this file
> and free dinode when inode still remain in memory on this node,
> which is not correct and may trigger BUG. So __ocfs2_mknod_locked
> should return error when ocfs2_create_new_inode_locks() failed.
> 
>               Node_1                              Node_2
> create fileA, call ocfs2_mknod()
>   -> ocfs2_get_init_inode(), allocate inodeA
>   -> ocfs2_claim_new_inode(), claim dinode(dinodeA)
>   -> call ocfs2_create_new_inode_locks(),
>      create open lock failed, return error
>   -> __ocfs2_mknod_locked return success
>             
>                                                 unlink fileA
>                                                 try open lock succeed,
>                                                 and free dinodeA
> 
> create another file, call ocfs2_mknod()
>   -> ocfs2_get_init_inode(), allocate inodeB
>   -> ocfs2_claim_new_inode(), as Node_2 had freed dinodeA,
>      so claim dinodeA and update generation for dinodeA
> 
> call __ocfs2_drop_dl_inodes()->ocfs2_delete_inode()
> to free inodeA, and finally triggers BUG
> on(inode->i_generation != le32_to_cpu(fe->i_generation))
> in function ocfs2_inode_lock_update().

Wow, that's a deep race, and it's some salty old code.  I think I buy
your description of the problem.  I'm trying to figure out why we didn't
hit this before.

What workload or tests triggered this?  Do you know why
ocfs2_create_new_inode_locks() failed in the first place?  I suspect it
almost never fails, which is why we haven't seen this issue.  Also,
which cluster stack was involved?

Finally, have you tested the result?  I believe that the iput()
machinery will do the right thing, but tests are better than my
intuition.

Joel

> 
> Signed-off-by: joyce.xue <xuejiufei@huawei.com>
> ---
>  fs/ocfs2/namei.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/fs/ocfs2/namei.c b/fs/ocfs2/namei.c
> index 3683643..63f9692 100644
> --- a/fs/ocfs2/namei.c
> +++ b/fs/ocfs2/namei.c
> @@ -576,9 +576,6 @@ static int __ocfs2_mknod_locked(struct inode *dir,
>  			mlog_errno(status);
>  	}
>  
> -	status = 0; /* error in ocfs2_create_new_inode_locks is not
> -		     * critical */
> -
>  leave:
>  	if (status < 0) {
>  		if (*new_fe_bh) {
> -- 
> 1.8.4.3
> 
> 
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			jlbec at evilplan.org