On fri, 14 Sep 2012 11:26:20 -0400, Josef Bacik wrote:
> So we start our freeze, somebody comes in and does an fsync() on a file
> where we have to commit a transaction for whatever reason, and we will
> deadlock because the freeze is waiting on FS_FREEZE people to stop writing
> to the file system, but the transaction is waiting for its free space inodes
> to be written out, which are in turn waiting on sb_start_intwrite while
> trying to write the file extents. To fix this we'll just skip the
> sb_start_intwrite() if we TRANS_JOIN_NOLOCK since we're being waited on by a
> transaction commit so we're safe wrt to freeze and this will keep us from
> deadlocking. Thanks,
>
> Signed-off-by: Josef Bacik <jbacik@xxxxxxxxxxxx>
> ---
> fs/btrfs/transaction.c | 10 +++++++++-
> 1 files changed, 9 insertions(+), 1 deletions(-)
>
> diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
> index c9265a6..ba74dfb 100644
> --- a/fs/btrfs/transaction.c
> +++ b/fs/btrfs/transaction.c
> @@ -342,7 +342,15 @@ again:
> if (!h)
> return ERR_PTR(-ENOMEM);
>
> - if (!__sb_start_write(root->fs_info->sb, SB_FREEZE_FS, false)) {
> + /*
> + * If we are JOIN_NOLOCK we're already committing a transaction and
> + * waiting on this guy, so we don't need to do the sb_start_intwrite
> + * because we're already holding a ref. We need this because we could
> + * have raced in and did an fsync() on a file which can kick a commit
> + * and then we deadlock with somebody doing a freeze.
> + */
> + if (type != TRANS_JOIN_NOLOCK &&
> + !__sb_start_write(root->fs_info->sb, SB_FREEZE_FS, false)) {
> if (type == TRANS_JOIN_FREEZE)
> return ERR_PTR(-EPERM);
> sb_start_intwrite(root->fs_info->sb);
>
This patch forgets to deal with it in __btrfs_end_transaction(), or the freeze counter
will be wrong.
Thanks
Miao
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