On 10/23/2014 11:54 AM, Chris Friesen wrote:
Basically it looks like we have a circular dependency involving the inode->i_data_sem rt_mutex, the PG_writeback bit, and the BJ_Shadow list. It goes something like this: jbd2_journal_commit_transaction: 1) set page for writeback (set PG_writeback bit) 2) put jbd2 journal head on BJ_Shadow list 3) sleep on PG_writeback bit waiting for page writeback complete ext4_da_writepages: 1) ext4_map_blocks() acquires inode->i_data_sem for writing 2) do_get_write_access() sleeps waiting for jbd2 journal head to come off the BJ_Shadow list At this point the flush code can't run because it can't acquire inode->i_data_sem for reading, so the page will never get written out. Deadlock.
Just curious...would we expect lockdep to detect this sort of thing? I wasn't sure if the introduction of the two wait queues would cause complications.
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