On Friday, December 23, 2016 03:00:18 PM Chandan Rajendra wrote: > The following deadlock is seen when executing generic/113 test, > > > ---------------------------------------------------------+---------------------------------------------------- > Direct I/O task Fast fsync task > > ---------------------------------------------------------+---------------------------------------------------- > btrfs_direct_IO > __blockdev_direct_IO > do_blockdev_direct_IO > do_direct_IO > btrfs_get_blocks_direct > while (blocks needs to written) > get_more_blocks (first iteration) > btrfs_get_blocks_direct > btrfs_create_dio_extent > down_read(&BTRFS_I(inode) >dio_sem) > Create and add extent map and ordered extent > up_read(&BTRFS_I(inode) >dio_sem) > btrfs_sync_file > > btrfs_log_dentry_safe > > btrfs_log_inode_parent > > btrfs_log_inode > > btrfs_log_changed_extents > > down_write(&BTRFS_I(inode) >dio_sem) > Collect > new extent maps and ordered extents > wait for > ordered extent completion > get_more_blocks (second iteration) > btrfs_get_blocks_direct > btrfs_create_dio_extent > down_read(&BTRFS_I(inode) >dio_sem) > > -------------------------------------------------------------------------------------------------------------- > > In the above description, Btrfs direct I/O code path has not yet started > submitting bios for file range covered by the initial ordered > extent. Meanwhile, The fast fsync task obtains the write semaphore and > waits for I/O on the ordered extent to get completed. However, the > Direct I/O task is now blocked on obtaining the read semaphore. > > To resolve the deadlock, this commit modifies the Direct I/O code path > to obtain the read semaphore before invoking > __blockdev_direct_IO(). The semaphore is then given up after > __blockdev_direct_IO() returns. This allows the Direct I/O code to > complete I/O on all the ordered extents it creates. >
Btw, I was able to reproduce the issue on kdave/for-next branch with "Merge branch 'for-next-next-4.9-20161125' into for-next-20161125" as the topmost commit. The issue cannot be reproduced yet on latest code available from kdave/for-next branch. -- chandan -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
