[Devel] [PATCH] fs/fuse kio: satisfy pure FALLOC_FL_KEEP_SIZE immediately

[Kirill Tkhai]

On 24.12.2018 15:54, Pavel Butsykin wrote:
> Fallocate without mutex lock can race with setattr size request, as a result,
> may be various problems, including incorrectly changed file size. At the same
> time pure FALLOC_FL_KEEP_SIZE for vstorage is just nope, so we can immediately

man 2 fallocate:

  "Specifying  the FALLOC_FL_ZERO_RANGE flag (available since Linux 3.15) in mode zeros space in the byte range starting at offset and
   continuing for len bytes.  Within the specified range, blocks are preallocated for the regions that span the  holes  in  the  file.
   After a successful call, subsequent reads from this range will return zeros".

So, this patch makes pcs_fuse_kdirect() complete a request without error
and without content changing, while userspace thinks the range was zeroed.
It's wrong.

> complete fallocate with mode == FALLOC_FL_KEEP_SIZE. Also move mutex_is_locked,
> since all other mode combinations either have to be under mutex or not valid.
> 
> #VSTOR-19317
> 
> Signed-off-by: Pavel Butsykin <pbutsykin at virtuozzo.com>
> ---
>  fs/fuse/kio/pcs/pcs_fuse_kdirect.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/fuse/kio/pcs/pcs_fuse_kdirect.c b/fs/fuse/kio/pcs/pcs_fuse_kdirect.c
> index de54fedeb5e4..89866370a341 100644
> --- a/fs/fuse/kio/pcs/pcs_fuse_kdirect.c
> +++ b/fs/fuse/kio/pcs/pcs_fuse_kdirect.c
> @@ -924,9 +924,11 @@ static void pcs_fuse_submit(struct pcs_fuse_cluster *pfc, struct fuse_req *req,
>  		if (inarg->offset >= di->fileinfo.attr.size)
>  			inarg->mode &= ~FALLOC_FL_ZERO_RANGE;
>  
> +		if (inarg->mode == FALLOC_FL_KEEP_SIZE)
> +			break; /* NOPE */

This is untidy to add new branch, which makes further "if (inarg->mode & FALLOC_FL_KEEP_SIZE)"
check a dead code.

> +
> +		WARN_ON_ONCE(!mutex_is_locked(&fi->inode.i_mutex));
>  		if (inarg->mode & (FALLOC_FL_ZERO_RANGE|FALLOC_FL_PUNCH_HOLE)) {
> -			WARN_ON_ONCE(!mutex_is_locked(&fi->inode.i_mutex));
> -
>  			if ((inarg->offset & (PAGE_SIZE - 1)) || (inarg->length & (PAGE_SIZE - 1))) {
>  				r->req.out.h.error = -EINVAL;
>  				goto error;
>