On Tue 19-04-22 10:31:39, Harshad Shirwadkar wrote:
> From: Harshad Shirwadkar <harshadshirwadkar@xxxxxxxxx>
>
> If the inode that's being requested to track using ext4_fc_track_inode
> is being committed, then wait until the inode finishes the
> commit. Also, add calls to ext4_fc_track_inode at the right places.
>
> With this patch, now calling ext4_reserve_inode_write() results in
> inode being tracked for next fast commit. A subtle lock ordering
> requirement with i_data_sem (which is documented in the code) requires
> that ext4_fc_track_inode() be called before grabbing i_data_sem. So,
> this patch also adds explicit ext4_fc_track_inode() calls in places
> where i_data_sem grabbed.
>
> Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@xxxxxxxxx>
> ---
> fs/ext4/fast_commit.c | 38 ++++++++++++++++++++++++++++++++++++++
> fs/ext4/inline.c | 3 +++
> fs/ext4/inode.c | 5 ++++-
> 3 files changed, 45 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ext4/fast_commit.c b/fs/ext4/fast_commit.c
> index c278060a15bc..55f4c5ddd8e5 100644
> --- a/fs/ext4/fast_commit.c
> +++ b/fs/ext4/fast_commit.c
> + /*
> + * If we come here, we may sleep while waiting for the inode to
> + * commit. We shouldn't be holding i_data_sem in write mode when we go
> + * to sleep since the commit path needs to grab the lock while
> + * committing the inode.
> + */
> + WARN_ON(lockdep_is_held_type(&ei->i_data_sem, 1));
Note that we can deadlock even if we had i_data_sem for reading because
another reader is not allowed to get the rwsem if there is writer waiting
for it. So we need to check even that case here.
> + while (ext4_test_inode_state(inode, EXT4_STATE_FC_COMMITTING)) {
> +#if (BITS_PER_LONG < 64)
> + DEFINE_WAIT_BIT(wait, &ei->i_state_flags,
> + EXT4_STATE_FC_COMMITTING);
> + wq = bit_waitqueue(&ei->i_state_flags,
> + EXT4_STATE_FC_COMMITTING);
> +#else
> + DEFINE_WAIT_BIT(wait, &ei->i_flags,
> + EXT4_STATE_FC_COMMITTING);
> + wq = bit_waitqueue(&ei->i_flags,
> + EXT4_STATE_FC_COMMITTING);
> +#endif
> + prepare_to_wait(wq, &wait.wq_entry, TASK_UNINTERRUPTIBLE);
> + if (ext4_test_inode_state(inode, EXT4_STATE_FC_COMMITTING))
> + schedule();
> + finish_wait(wq, &wait.wq_entry);
> + }
> +
> ret = ext4_fc_track_template(handle, inode, __track_inode, NULL, 1);
> trace_ext4_fc_track_inode(handle, inode, ret);
As we discussed in the call we should tell lockdep that this is equivalent
to lock+unlock of let's say fc_committing_lock and the fastcommit code
setting / clearing EXT4_STATE_FC_COMMITTING is equivalent to lock / unlock
of fc_committing_lock. That way we get proper lockdep tracking of this
waiting primitive.
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
