RE: [PATCH v5 1/5] libfs: Return ENOSPC when the directory offset range is exhausted

[David Laight <David.Laight@ACULAB.COM>]

From: cel@kernel.org
> Sent: 15 December 2024 18:58
> 
> From: Chuck Lever <chuck.lever@oracle.com>
> 
> Testing shows that the EBUSY error return from mtree_alloc_cyclic()
> leaks into user space. The ERRORS section of "man creat(2)" says:
> 
> >	EBUSY	O_EXCL was specified in flags and pathname refers
> >		to a block device that is in use by the system
> >		(e.g., it is mounted).
> 
> ENOSPC is closer to what applications expect in this situation.
> 
> Note that the normal range of simple directory offset values is
> 2..2^63, so hitting this error is going to be rare to impossible.
> 
> Fixes: 6faddda69f62 ("libfs: Add directory operations for stable offsets")
> Cc: <stable@vger.kernel.org> # v6.9+
> Reviewed-by: Jeff Layton <jlayton@kernel.org>
> Reviewed-by: Yang Erkun <yangerkun@huawei.com>
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  fs/libfs.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/libfs.c b/fs/libfs.c
> index 748ac5923154..f6d04c69f195 100644
> --- a/fs/libfs.c
> +++ b/fs/libfs.c
> @@ -292,7 +292,9 @@ int simple_offset_add(struct offset_ctx *octx, struct dentry *dentry)
> 
>  	ret = mtree_alloc_cyclic(&octx->mt, &offset, dentry, DIR_OFFSET_MIN,
>  				 LONG_MAX, &octx->next_offset, GFP_KERNEL);
> -	if (ret < 0)
> +	if (unlikely(ret == -EBUSY))
> +		return -ENOSPC;
> +	if (unlikely(ret < 0))
>  		return ret;

You've just added an extra comparison to a hot path.
Doing:
	if (ret < 0)
		return ret == -EBUSY ? -ENOSPC : ret;
would be better.

	David

> 
>  	offset_set(dentry, offset);
> --
> 2.47.0
> 

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