Re: [PATCH] btrfs: skip file_extent generation check for free_space_inode in run_delalloc_nocow

From: Filipe Manana <fdmanana@gmail.com>
To: Lu Fengqi <lufq.fnst@cn.fujitsu.com>
Cc: linux-btrfs <linux-btrfs@vger.kernel.org>
Subject: Re: [PATCH] btrfs: skip file_extent generation check for free_space_inode in run_delalloc_nocow
Date: Thu, 29 Nov 2018 10:32:33 +0000	[thread overview]
Message-ID: <CAL3q7H5jjpGqpndW1QWcLewOYpogp_n_qY7kKGBUQbTRdphK8A@mail.gmail.com> (raw)
In-Reply-To: <20181129093132.25147-1-lufq.fnst@cn.fujitsu.com>

On Thu, Nov 29, 2018 at 9:32 AM Lu Fengqi <lufq.fnst@cn.fujitsu.com> wrote:
>
> The btrfs/001 with inode_cache mount option will encounter the following
> warning:

"The test case btrfs/001 ..."

>
> WARNING: CPU: 1 PID: 23700 at fs/btrfs/inode.c:956 cow_file_range.isra.19+0x32b/0x430 [btrfs]
> CPU: 1 PID: 23700 Comm: btrfs Kdump: loaded Tainted: G        W  O      4.20.0-rc4-custom+ #30
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
> RIP: 0010:cow_file_range.isra.19+0x32b/0x430 [btrfs]
> Call Trace:
>  ? free_extent_buffer+0x46/0x90 [btrfs]
>  run_delalloc_nocow+0x455/0x900 [btrfs]
>  btrfs_run_delalloc_range+0x1a7/0x360 [btrfs]
>  writepage_delalloc+0xf9/0x150 [btrfs]
>  __extent_writepage+0x125/0x3e0 [btrfs]
>  extent_write_cache_pages+0x1b6/0x3e0 [btrfs]
>  ? __wake_up_common_lock+0x63/0xc0
>  extent_writepages+0x50/0x80 [btrfs]
>  do_writepages+0x41/0xd0
>  ? __filemap_fdatawrite_range+0x9e/0xf0
>  __filemap_fdatawrite_range+0xbe/0xf0
>  btrfs_fdatawrite_range+0x1b/0x50 [btrfs]
>  __btrfs_write_out_cache+0x42c/0x480 [btrfs]
>  btrfs_write_out_ino_cache+0x84/0xd0 [btrfs]
>  btrfs_save_ino_cache+0x551/0x660 [btrfs]
>  commit_fs_roots+0xc5/0x190 [btrfs]
>  btrfs_commit_transaction+0x2bf/0x8d0 [btrfs]
>  btrfs_mksubvol+0x48d/0x4d0 [btrfs]
>  btrfs_ioctl_snap_create_transid+0x170/0x180 [btrfs]
>  btrfs_ioctl_snap_create_v2+0x124/0x180 [btrfs]
>  btrfs_ioctl+0x123f/0x3030 [btrfs]
>
> The file extent generation of the free space inode is equal to the last
> snapshot of the file root, so the inode will be passed to cow_file_rage.
> But the inode was created and its extents were preallocated in
> btrfs_save_ino_cache, there are no cow copies on disk.
>
> The preallocated extents don't present on disk, and the

The preallocated extent is not yet in the extent tree, and the ...
(singular, it's only used for each space cache)

> btrfs_cross_ref_exist will ignore the -ENOENT returned by
> check_committed_ref, so we can directly write the inode to the disk.
>
> Fixes: 78d4295b1eee ("btrfs: lift some btrfs_cross_ref_exist checks in nocow path")
> Signed-off-by: Lu Fengqi <lufq.fnst@cn.fujitsu.com>

The code changes look good to me.

Reviewed-by: Filipe Manana <fdmanana@suse.com>

Thanks.

> ---
>  fs/btrfs/inode.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index d54bdef16d8d..9c5e9629eb6c 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -1369,7 +1369,8 @@ static noinline int run_delalloc_nocow(struct inode *inode,
>                          * Do the same check as in btrfs_cross_ref_exist but
>                          * without the unnecessary search.
>                          */
> -                       if (btrfs_file_extent_generation(leaf, fi) <=
> +                       if (!nolock &&
> +                           btrfs_file_extent_generation(leaf, fi) <=
>                             btrfs_root_last_snapshot(&root->root_item))
>                                 goto out_check;
>                         if (extent_type == BTRFS_FILE_EXTENT_REG && !force)
> --
> 2.19.2
>
>
>

-- 
Filipe David Manana,

“Whether you think you can, or you think you can't — you're right.”