RE: [f2fs-dev] [PATCH 5/5] f2fs: check the node block address of newly allocated nid

[Chao Yu]

Hi Jaegeuk,

> -----Original Message-----
> From: Jaegeuk Kim [mailto:jaegeuk@xxxxxxxxxx]
> Sent: Tuesday, August 18, 2015 4:46 PM
> To: linux-kernel@xxxxxxxxxxxxxxx; linux-fsdevel@xxxxxxxxxxxxxxx;
> linux-f2fs-devel@xxxxxxxxxxxxxxxxxxxxx
> Cc: Jaegeuk Kim
> Subject: [f2fs-dev] [PATCH 5/5] f2fs: check the node block address of newly allocated nid
> 
> This patch adds a routine which checks the block address of newly allocated nid.
> If an nid has already allocated by other thread due to subtle data races, it
> will result in filesystem corruption.
> So, it needs to check whether its block address was already allocated or not
> in prior to nid allocation as the last chance.
> 
> Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> ---
>  fs/f2fs/node.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> index 3cc32b8..6bef5a2 100644
> --- a/fs/f2fs/node.c
> +++ b/fs/f2fs/node.c
> @@ -1573,6 +1573,8 @@ retry:
> 
>  	/* We should not use stale free nids created by build_free_nids */
>  	if (nm_i->fcnt && !on_build_free_nids(nm_i)) {
> +		struct node_info ni;
> +
>  		f2fs_bug_on(sbi, list_empty(&nm_i->free_nid_list));
>  		list_for_each_entry(i, &nm_i->free_nid_list, list)
>  			if (i->state == NID_NEW)
> @@ -1583,6 +1585,13 @@ retry:
>  		i->state = NID_ALLOC;
>  		nm_i->fcnt--;
>  		spin_unlock(&nm_i->free_nid_list_lock);
> +
> +		/* check nid is allocated already */
> +		get_node_info(sbi, *nid, &ni);
> +		if (ni.blk_addr != NULL_ADDR) {

I didn't get it, why free nid is with non-NULL blkaddr?
Could you please explain more about this?

> +			alloc_nid_done(sbi, *nid);

Will another thread call alloc_nid_done too, making this free nid being
released again?

Thanks,

> +			goto retry;
> +		}
>  		return true;
>  	}
>  	spin_unlock(&nm_i->free_nid_list_lock);
> --
> 2.1.1
> 
> 
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