On Tue 11-02-20 21:55:00, zhangyi (F) wrote:
> Commit 904cdbd41d74 ("jbd2: clear dirty flag when revoking a buffer from
> an older transaction") set the BH_Freed flag when forgetting a metadata
> buffer which belongs to the committing transaction, it indicate the
> committing process clear dirty bits when it is done with the buffer. But
> it also clear the BH_Mapped flag at the same time, which may trigger
> below NULL pointer oops when block_size < PAGE_SIZE.
>
> rmdir 1 kjournald2 mkdir 2
> jbd2_journal_commit_transaction
> commit transaction N
> jbd2_journal_forget
> set_buffer_freed(bh1)
> jbd2_journal_commit_transaction
> commit transaction N+1
> ...
> clear_buffer_mapped(bh1)
> ext4_getblk(bh2 ummapped)
> ...
> grow_dev_page
> init_page_buffers
> bh1->b_private=NULL
> bh2->b_private=NULL
> jbd2_journal_put_journal_head(jh1)
> __journal_remove_journal_head(hb1)
> jh1 is NULL and trigger oops
>
> *) Dir entry block bh1 and bh2 belongs to one page, and the bh2 has
> already been unmapped.
>
> For the metadata buffer we forgetting, we should always keep the mapped
> flag and clear the dirty flags is enough, so this patch pick out the
> these buffers and keep their BH_Mapped flag.
>
> Fixes: 904cdbd41d74 ("jbd2: clear dirty flag when revoking a buffer from an older transaction")
> Signed-off-by: zhangyi (F) <yi.zhang@xxxxxxxxxx>
> ---
> fs/jbd2/commit.c | 20 ++++++++++++++++----
> 1 file changed, 16 insertions(+), 4 deletions(-)
>
> diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
> index ecc2ea5f1b59..8f6f4ddd8b78 100644
> --- a/fs/jbd2/commit.c
> +++ b/fs/jbd2/commit.c
> @@ -985,12 +985,24 @@ void jbd2_journal_commit_transaction(journal_t *journal)
> * pagesize and it is attached to the last partial page.
> */
> if (buffer_freed(bh) && !jh->b_next_transaction) {
> + struct address_space *mapping;
> +
> clear_buffer_freed(bh);
> clear_buffer_jbddirty(bh);
> - clear_buffer_mapped(bh);
> - clear_buffer_new(bh);
> - clear_buffer_req(bh);
> - bh->b_bdev = NULL;
> + /*
> + * We can (and need to) unmap buffer only for normal
> + * mappings. Block device buffers need to stay mapped
> + * all the time. We need to be careful about the check
> + * because the data page mapping can get cleared under
> + * our hands.
> + */
> + mapping = READ_ONCE(bh->b_page->mapping);
> + if (!(mapping && sb_is_blkdev_sb(mapping->host->i_sb))) {
As I wrote in my other email, we don't have to be that aggressive and this
condition could actually be (mapping && !sb_is_blkdev_sb()) but I guess it
doesn't really matter. You can add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> + clear_buffer_mapped(bh);
> + clear_buffer_new(bh);
> + clear_buffer_req(bh);
> + bh->b_bdev = NULL;
> + }
> }
>
> if (buffer_jbddirty(bh)) {
> --
> 2.17.2
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
