Hello, Dave. On Fri, Aug 21, 2015 at 09:04:51AM +1000, Dave Chinner wrote: > > Maybe I'm misunderstanding the code but all xfs_writepage() calls are > > from unbound workqueues - the writeback workers - while > > xfs_setfilesize() are from bound workqueues, so I wondered why that > > was and looked at the code and the setsize functions are run off of a > > separate work item which is queued from the end_bio callback and I > > can't tell who would be waiting for them. Dave, what am I missing? > > xfs_setfilesize runs transactions, so it can't be run from IO > completion context as it needs to block (i.e. on log space or inode > locks). It also can't block log IO completion, nor metadata Io > completion, as only log IO completion can free log space, and the > inode lock might be waiting on metadata buffer IO completion (e.g. > during delayed allocation). Hence we have multiple IO completion > workqueues to keep these things separated and deadlock free. i.e. > they all get punted to a workqueue where they are then processed in > a context that can block safely. I'm still a bit confused. What prevents the following from happening? 1. io completion of last dirty page of an inode and work item for xfs_setfilesize() is queued. 2. inode removed from dirty list. 3. __sync_filesystem() invokes sync_inodes_sb(). There are no dirty pages, so it finishes. 4. xfs_fs_sync_fs() is called which calls _xfs_log_force() but the work item from #1 hasn't run yet, so the size update isn't written out. 5. Crash. Is it that _xfs_log_force() waits for the setfilesize transaction created during writepage? Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
