On Wed 10-02-21 10:57:39, Alexander Lochmann wrote:
> Some members of transaction_t are allowed to be read without
> any lock being held if consistency doesn't matter.
> Based on LockDoc's findings, we extended the locking
> documentation of those members.
> Each one of them is marked with a short comment:
> "no lock for quick racy checks".
>
> Signed-off-by: Alexander Lochmann <[email protected]>
> Signed-off-by: Horst Schirmeier <[email protected]>
Thanks for the patch! Some comments below...
> ---
> include/linux/jbd2.h | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
> index 99d3cd051ac3..18f77d9b1745 100644
> --- a/include/linux/jbd2.h
> +++ b/include/linux/jbd2.h
> @@ -594,18 +594,18 @@ struct transaction_s
> */
> unsigned long t_log_start;
>
> - /* Number of buffers on the t_buffers list [j_list_lock] */
> + /* Number of buffers on the t_buffers list [j_list_lock, no lock for
> quick racy checks] */
> int t_nr_buffers;
So this case is actually somewhat different now that I audited the uses.
There are two types of users - commit code (fs/jbd2/commit.c) and others.
Other users properly use j_list_lock to access t_nr_buffers. Commit code
does not use any locks because committing transaction is fully in
ownership of the jbd2 thread and all other users need to check & wait for
commit to be finished before doing anything with the transaction's buffers.
> /*
> * Doubly-linked circular list of all buffers reserved but not yet
> - * modified by this transaction [j_list_lock]
> + * modified by this transaction [j_list_lock, no lock for quick racy
> checks]
> */
> struct journal_head *t_reserved_list;
>
> /*
> * Doubly-linked circular list of all metadata buffers owned by this
> - * transaction [j_list_lock]
> + * transaction [j_list_lock, no lock for quick racy checks]
> */
> struct journal_head *t_buffers;
>
> @@ -631,7 +631,7 @@ struct transaction_s
> /*
> * Doubly-linked circular list of metadata buffers being shadowed by log
> * IO. The IO buffers on the iobuf list and the shadow buffers on this
> - * list match each other one for one at all times. [j_list_lock]
> + * list match each other one for one at all times. [j_list_lock, no
> lock for quick racy checks]
> */
> struct journal_head *t_shadow_list;
The above three cases are the same as t_reserved_list.
Honza
--
Jan Kara <[email protected]>
SUSE Labs, CR
