Re: [PATCH v2] ceph: request Fw caps before updating the mtime in ceph_write_iter

[Xiubo Li <xiubli@redhat.com>]

On 8/12/21 1:37 AM, Jeff Layton wrote:
> The current code will update the mtime and then try to get caps to
> handle the write. If we end up having to request caps from the MDS, then
> the mtime in the cap grant will clobber the updated mtime and it'll be
> lost.
>
> This is most noticable when two clients are alternately writing to the
> same file. Fw caps are continually being granted and revoked, and the
> mtime ends up stuck because the updated mtimes are always being
> overwritten with the old one.
>
> Fix this by changing the order of operations in ceph_write_iter. Get the
> caps much earlier, and only update the times afterward. Also, make sure
> we check the NEARFULL conditions before making any changes to the inode.
>
> URL: https://tracker.ceph.com/issues/46574
> Reported-by: Jozef Kováč <kovac@firma.zoznam.sk>
> Signed-off-by: Jeff Layton <jlayton@kernel.org>
> ---
>   fs/ceph/file.c | 35 ++++++++++++++++++-----------------
>   1 file changed, 18 insertions(+), 17 deletions(-)
>
> v2: fix error handling -- make sure we release i_rwsem on error exit
>
> diff --git a/fs/ceph/file.c b/fs/ceph/file.c
> index d1755ac1d964..da856bd5eaa5 100644
> --- a/fs/ceph/file.c
> +++ b/fs/ceph/file.c
> @@ -1722,22 +1722,6 @@ static ssize_t ceph_write_iter(struct kiocb *iocb, struct iov_iter *from)
>   		goto out;
>   	}
>   
> -	err = file_remove_privs(file);
> -	if (err)
> -		goto out;
> -
> -	err = file_update_time(file);
> -	if (err)
> -		goto out;
> -
> -	inode_inc_iversion_raw(inode);
> -
> -	if (ci->i_inline_version != CEPH_INLINE_NONE) {
> -		err = ceph_uninline_data(file, NULL);
> -		if (err < 0)
> -			goto out;
> -	}
> -
>   	down_read(&osdc->lock);
>   	map_flags = osdc->osdmap->flags;
>   	pool_flags = ceph_pg_pool_flags(osdc->osdmap, ci->i_layout.pool_id);
> @@ -1748,6 +1732,12 @@ static ssize_t ceph_write_iter(struct kiocb *iocb, struct iov_iter *from)
>   		goto out;
>   	}
>   
> +	if (ci->i_inline_version != CEPH_INLINE_NONE) {
> +		err = ceph_uninline_data(file, NULL);
> +		if (err < 0)
> +			goto out;
> +	}
> +
>   	dout("aio_write %p %llx.%llx %llu~%zd getting caps. i_size %llu\n",
>   	     inode, ceph_vinop(inode), pos, count, i_size_read(inode));
>   	if (fi->fmode & CEPH_FILE_MODE_LAZY)
> @@ -1759,6 +1749,16 @@ static ssize_t ceph_write_iter(struct kiocb *iocb, struct iov_iter *from)
>   	if (err < 0)
>   		goto out;
>   
> +	err = file_remove_privs(file);
> +	if (err)
> +		goto out_caps;
> +
> +	err = file_update_time(file);
> +	if (err)
> +		goto out_caps;
> +
> +	inode_inc_iversion_raw(inode);
> +
>   	dout("aio_write %p %llx.%llx %llu~%zd got cap refs on %s\n",
>   	     inode, ceph_vinop(inode), pos, count, ceph_cap_string(got));
>   
> @@ -1822,7 +1822,6 @@ static ssize_t ceph_write_iter(struct kiocb *iocb, struct iov_iter *from)
>   		if (ceph_quota_is_max_bytes_approaching(inode, iocb->ki_pos))
>   			ceph_check_caps(ci, 0, NULL);
>   	}
> -
>   	dout("aio_write %p %llx.%llx %llu~%u  dropping cap refs on %s\n",
>   	     inode, ceph_vinop(inode), pos, (unsigned)count,
>   	     ceph_cap_string(got));
> @@ -1842,6 +1841,8 @@ static ssize_t ceph_write_iter(struct kiocb *iocb, struct iov_iter *from)
>   	}
>   
>   	goto out_unlocked;
> +out_caps:
> +	ceph_put_cap_refs(ci, got);
>   out:
>   	if (direct_lock)
>   		ceph_end_io_direct(inode);

The fuse client is already correctly doing this.

LGTM

Reviewed-by: Xiubo Li <xiubli@redhat.com>