On Mon, Jan 19, 2015 at 03:42:41PM +0800, Qu Wenruo wrote:
> The fix is to check if the fs is frozen, if the fs is frozen, just
> return and waiting for the next transaction.
>
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -1000,6 +1000,14 @@ int btrfs_sync_fs(struct super_block *sb, int wait)
> */
> if (fs_info->pending_changes == 0)
> return 0;
> + /*
> + * Test if the fs is frozen, or start_trasaction
> + * will deadlock on itself.
> + */
> + if (__sb_start_write(sb, SB_FREEZE_FS, false))
> + __sb_end_write(sb, SB_FREEZE_FS);
> + else
> + return 0;
I'm not sure this is the right fix. We should use either
mnt_want_write_file or sb_start_write around the start/commit functions.
The fs may be frozen already, but we also have to catch transition to
that state, or RO remount.
Also, returning 0 is not right, the ioctl actually skipped the expected
work.
> trans = btrfs_start_transaction(root, 0);
> } else {
> return PTR_ERR(trans);
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