From 28a535f9a0df060569dcc786e5bc2e1de43d7dc7 Mon Sep 17 00:00:00 2001 From: Dmitry Monakhov Date: Sat, 29 Sep 2012 00:14:55 -0400 Subject: ext4: completed_io locking cleanup Current unwritten extent conversion state-machine is very fuzzy. - For unknown reason it performs conversion under i_mutex. What for? My diagnosis: We already protect extent tree with i_data_sem, truncate and punch_hole should wait for DIO, so the only data we have to protect is end_io->flags modification, but only flush_completed_IO and end_io_work modified this flags and we can serialize them via i_completed_io_lock. Currently all these games with mutex_trylock result in the following deadlock truncate: kworker: ext4_setattr ext4_end_io_work mutex_lock(i_mutex) inode_dio_wait(inode) ->BLOCK DEADLOCK<- mutex_trylock() inode_dio_done() #TEST_CASE1_BEGIN MNT=/mnt_scrach unlink $MNT/file fallocate -l $((1024*1024*1024)) $MNT/file aio-stress -I 100000 -O -s 100m -n -t 1 -c 10 -o 2 -o 3 $MNT/file sleep 2 truncate -s 0 $MNT/file #TEST_CASE1_END Or use 286's xfstests https://github.com/dmonakhov/xfstests/blob/devel/286 This patch makes state machine simple and clean: (1) xxx_end_io schedule final extent conversion simply by calling ext4_add_complete_io(), which append it to ei->i_completed_io_list NOTE1: because of (2A) work should be queued only if ->i_completed_io_list was empty, otherwise the work is scheduled already. (2) ext4_flush_completed_IO is responsible for handling all pending end_io from ei->i_completed_io_list Flushing sequence consists of following stages: A) LOCKED: Atomically drain completed_io_list to local_list B) Perform extents conversion C) LOCKED: move converted io's to to_free list for final deletion This logic depends on context which we was called from. D) Final end_io context destruction NOTE1: i_mutex is no longer required because end_io->flags modification is protected by ei->ext4_complete_io_lock Full list of changes: - Move all completion end_io related routines to page-io.c in order to improve logic locality - Move open coded logic from various xx_end_xx routines to ext4_add_complete_io() - remove EXT4_IO_END_FSYNC - Improve SMP scalability by removing useless i_mutex which does not protect io->flags anymore. - Reduce lock contention on i_completed_io_lock by optimizing list walk. - Rename ext4_end_io_nolock to end4_end_io and make it static - Check flush completion status to ext4_ext_punch_hole(). Because it is not good idea to punch blocks from corrupted inode. Changes since V3 (in request to Jan's comments): Fall back to active flush_completed_IO() approach in order to prevent performance issues with nolocked DIO reads. Changes since V2: Fix use-after-free caused by race truncate vs end_io_work Signed-off-by: Dmitry Monakhov Signed-off-by: "Theodore Ts'o" --- fs/ext4/indirect.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) (limited to 'fs/ext4/indirect.c') diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c index 830e1b2bf14..61f13e57975 100644 --- a/fs/ext4/indirect.c +++ b/fs/ext4/indirect.c @@ -807,11 +807,9 @@ ssize_t ext4_ind_direct_IO(int rw, struct kiocb *iocb, retry: if (rw == READ && ext4_should_dioread_nolock(inode)) { - if (unlikely(!list_empty(&ei->i_completed_io_list))) { - mutex_lock(&inode->i_mutex); + if (unlikely(!list_empty(&ei->i_completed_io_list))) ext4_flush_completed_IO(inode); - mutex_unlock(&inode->i_mutex); - } + ret = __blockdev_direct_IO(rw, iocb, inode, inode->i_sb->s_bdev, iov, offset, nr_segs, -- cgit v1.2.3-18-g5258