Re: [PATCH] NFS: don't raise i_size for DEALLOCATE in _nfs42_proc_fallocate()

["Anna Schumaker" <anna@kernel.org>]

Hi Joseph,

On Tue, Nov 3, 2026, at 1:16 AM, Joseph Qi wrote:
> _nfs42_proc_fallocate() raises i_size to offset + len on success, so
> that the cached size is not left stale when a delegation blocks the
> post-op attribute refresh.  The helper is shared by all three
> fallocate modes, but DEALLOCATE always carries FALLOC_FL_KEEP_SIZE
> and never extends the file on the server, so punching a hole that
> reaches past EOF now wrongly enlarges the cached i_size.
>
> The post-op update would normally restore the size from the returned
> attributes, but nfs_update_inode() applies a differing size only when
> no delegation is held, and then only when no write is in flight or the
> new size is larger:
>
> 	if (new_isize != cur_isize && !have_delegation) {
> 		if (!nfs_have_writebacks(inode) || new_isize > cur_isize)
> 			i_size_write(inode, new_isize);
> 	}
>
> With a concurrent mmap writer (nrequests != 0) or any outstanding
> delegation, the shrinking server size is therefore ignored and the
> client keeps reporting a file larger than the server has, in violation
> of KEEP_SIZE, until some later revalidation without writebacks happens
> to fix it up.
>
> Skip the i_size bump for the DEALLOCATE procedure.  ALLOCATE (mode 0)
> and ZERO_RANGE (which nfs42_fallocate() accepts only without
> FALLOC_FL_KEEP_SIZE) do extend the file when the range reaches past
> EOF, so they keep the update.
>
> Fixes: 35168eb947f2 ("NFS: fix eof updates after NFSv4.2 fallocate/zero-range")
> Cc: stable@vger.kernel.org
> Signed-off-by: Joseph Qi <joseph.qi@linux.alibaba.com>
> ---
>  fs/nfs/nfs42proc.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
>
> diff --git a/fs/nfs/nfs42proc.c b/fs/nfs/nfs42proc.c
> index ab86246fc364f..914499d30d47e 100644
> --- a/fs/nfs/nfs42proc.c
> +++ b/fs/nfs/nfs42proc.c
> @@ -84,7 +84,16 @@ static int _nfs42_proc_fallocate(struct rpc_message 
> *msg, struct file *filep,
>  		loff_t newsize = offset + len;
> 
>  		spin_lock(&inode->i_lock);
> -		if (newsize > i_size_read(inode))
> +		/*
> +		 * DEALLOCATE always carries FALLOC_FL_KEEP_SIZE and never
> +		 * extends the file on the server, so only ALLOCATE and
> +		 * ZERO_RANGE may raise i_size here.  A wrongly raised size
> +		 * can persist: nfs_update_inode() ignores a shrinking
> +		 * post-op size while writebacks are outstanding or a
> +		 * delegation is held.
> +		 */

Is the comment really necessary? It's just restating things from the commit
message, and could quickly go stale if the behavior of nfs_update_inode()
ever needs to change in the future.

Thanks,
Anna

> +		if (msg->rpc_proc != &nfs4_procedures[NFSPROC4_CLNT_DEALLOCATE] &&
> +		    newsize > i_size_read(inode))
>  			i_size_write(inode, newsize);
>  		nfs_set_cache_invalid(inode, NFS_INO_INVALID_BLOCKS);
>  		if (nfs_should_remove_suid(inode))
> -- 
> 2.39.3