On Fri, Dec 23, 2016 at 05:27:55PM +0530, Chandan Rajendra wrote: > On Friday, December 23, 2016 03:57:40 PM Chandan Rajendra wrote: > > 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. > > > > > > Maybe changes in upstream might have masked the issue in the recent > kdave/for-next branch. I say that because 'git bisect' resulted in the > following commit ... I guess that the for-next branch didn't revert this patch[1] as upstream did, so that generic/113 would complain, however, even w/o that patch, this fix is still required since the deadlock could be reproduced by running generic/113 with '-ofragment=data' and in fact Filipe has proposed a almost same fix but not a real patch in this thread [2]. [1]: Btrfs: adjust len of writes if following a preallocated extent https://patchwork.kernel.org/patch/9413129/ [2]: https://patchwork.kernel.org/patch/9445231/ Thanks, -liubo > > e3597e6090ddf40904dce6d0a5a404e2c490cac6 > Author: Chris Mason <clm@xxxxxx> > AuthorDate: Tue Nov 1 12:54:45 2016 -0700 > Commit: Chris Mason <clm@xxxxxx> > CommitDate: Tue Nov 1 12:54:45 2016 -0700 > > Parent: 570dd45 btrfs: fix races on root_log_ctx lists > Parent: 9d1032c btrfs: fix WARNING in btrfs_select_ref_head() > Merged: btrfs-next-for-linus-4.8 kdave-master linus-v4.7-rc6 local-v4.7-rc4 > Containing: direct-io-fsync-deadlock kdave-for-next > Follows: v4.8-rc8 (57) > Precedes: next-20161219 (30006) > > Merge branch 'for-4.9-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux into for-linus-4.9 > > 5 files changed, 29 insertions(+), 9 deletions(-) > fs/btrfs/extent-tree.c | 3 +++ > fs/btrfs/extent_io.c | 8 ++++---- > fs/btrfs/inode.c | 13 +++++++++---- > fs/btrfs/ioctl.c | 5 +++++ > fs/btrfs/relocation.c | 9 ++++++++- > > -- > chandan > > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
