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/page-io.c | 171 ++++++++++++++++++++++++++++++++++++------------------ 1 file changed, 113 insertions(+), 58 deletions(-) (limited to 'fs/ext4/page-io.c') diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c index 997002218228..5b24c407701b 100644 --- a/fs/ext4/page-io.c +++ b/fs/ext4/page-io.c @@ -71,6 +71,7 @@ void ext4_free_io_end(ext4_io_end_t *io) int i; BUG_ON(!io); + BUG_ON(!list_empty(&io->list)); BUG_ON(io->flag & EXT4_IO_END_UNWRITTEN); if (io->page) @@ -83,21 +84,14 @@ void ext4_free_io_end(ext4_io_end_t *io) kmem_cache_free(io_end_cachep, io); } -/* - * check a range of space and convert unwritten extents to written. - * - * Called with inode->i_mutex; we depend on this when we manipulate - * io->flag, since we could otherwise race with ext4_flush_completed_IO() - */ -int ext4_end_io_nolock(ext4_io_end_t *io) +/* check a range of space and convert unwritten extents to written. */ +static int ext4_end_io(ext4_io_end_t *io) { struct inode *inode = io->inode; loff_t offset = io->offset; ssize_t size = io->size; int ret = 0; - BUG_ON(!(io->flag & EXT4_IO_END_UNWRITTEN)); - ext4_debug("ext4_end_io_nolock: io 0x%p from inode %lu,list->next 0x%p," "list->prev 0x%p\n", io, inode->i_ino, io->list.next, io->list.prev); @@ -110,7 +104,6 @@ int ext4_end_io_nolock(ext4_io_end_t *io) "(inode %lu, offset %llu, size %zd, error %d)", inode->i_ino, offset, size, ret); } - io->flag &= ~EXT4_IO_END_UNWRITTEN; if (io->iocb) aio_complete(io->iocb, io->result, 0); @@ -122,51 +115,122 @@ int ext4_end_io_nolock(ext4_io_end_t *io) return ret; } -/* - * work on completed aio dio IO, to convert unwritten extents to extents - */ -static void ext4_end_io_work(struct work_struct *work) +static void dump_completed_IO(struct inode *inode) +{ +#ifdef EXT4FS_DEBUG + struct list_head *cur, *before, *after; + ext4_io_end_t *io, *io0, *io1; + unsigned long flags; + + if (list_empty(&EXT4_I(inode)->i_completed_io_list)) { + ext4_debug("inode %lu completed_io list is empty\n", + inode->i_ino); + return; + } + + ext4_debug("Dump inode %lu completed_io list\n", inode->i_ino); + list_for_each_entry(io, &EXT4_I(inode)->i_completed_io_list, list) { + cur = &io->list; + before = cur->prev; + io0 = container_of(before, ext4_io_end_t, list); + after = cur->next; + io1 = container_of(after, ext4_io_end_t, list); + + ext4_debug("io 0x%p from inode %lu,prev 0x%p,next 0x%p\n", + io, inode->i_ino, io0, io1); + } +#endif +} + +/* Add the io_end to per-inode completed end_io list. */ +void ext4_add_complete_io(ext4_io_end_t *io_end) { - ext4_io_end_t *io = container_of(work, ext4_io_end_t, work); - struct inode *inode = io->inode; - struct ext4_inode_info *ei = EXT4_I(inode); - unsigned long flags; + struct ext4_inode_info *ei = EXT4_I(io_end->inode); + struct workqueue_struct *wq; + unsigned long flags; + + BUG_ON(!(io_end->flag & EXT4_IO_END_UNWRITTEN)); + wq = EXT4_SB(io_end->inode->i_sb)->dio_unwritten_wq; spin_lock_irqsave(&ei->i_completed_io_lock, flags); - if (io->flag & EXT4_IO_END_IN_FSYNC) - goto requeue; - if (list_empty(&io->list)) { - spin_unlock_irqrestore(&ei->i_completed_io_lock, flags); - goto free; + if (list_empty(&ei->i_completed_io_list)) { + io_end->flag |= EXT4_IO_END_QUEUED; + queue_work(wq, &io_end->work); } + list_add_tail(&io_end->list, &ei->i_completed_io_list); + spin_unlock_irqrestore(&ei->i_completed_io_lock, flags); +} - if (!mutex_trylock(&inode->i_mutex)) { - bool was_queued; -requeue: - was_queued = !!(io->flag & EXT4_IO_END_QUEUED); - io->flag |= EXT4_IO_END_QUEUED; - spin_unlock_irqrestore(&ei->i_completed_io_lock, flags); - /* - * Requeue the work instead of waiting so that the work - * items queued after this can be processed. - */ - queue_work(EXT4_SB(inode->i_sb)->dio_unwritten_wq, &io->work); - /* - * To prevent the ext4-dio-unwritten thread from keeping - * requeueing end_io requests and occupying cpu for too long, - * yield the cpu if it sees an end_io request that has already - * been requeued. - */ - if (was_queued) - yield(); - return; +static int ext4_do_flush_completed_IO(struct inode *inode, + ext4_io_end_t *work_io) +{ + ext4_io_end_t *io; + struct list_head unwritten, complete, to_free; + unsigned long flags; + struct ext4_inode_info *ei = EXT4_I(inode); + int err, ret = 0; + + INIT_LIST_HEAD(&complete); + INIT_LIST_HEAD(&to_free); + + spin_lock_irqsave(&ei->i_completed_io_lock, flags); + dump_completed_IO(inode); + list_replace_init(&ei->i_completed_io_list, &unwritten); + spin_unlock_irqrestore(&ei->i_completed_io_lock, flags); + + while (!list_empty(&unwritten)) { + io = list_entry(unwritten.next, ext4_io_end_t, list); + BUG_ON(!(io->flag & EXT4_IO_END_UNWRITTEN)); + list_del_init(&io->list); + + err = ext4_end_io(io); + if (unlikely(!ret && err)) + ret = err; + + list_add_tail(&io->list, &complete); + } + /* It is important to update all flags for all end_io in one shot w/o + * dropping the lock.*/ + spin_lock_irqsave(&ei->i_completed_io_lock, flags); + while (!list_empty(&complete)) { + io = list_entry(complete.next, ext4_io_end_t, list); + io->flag &= ~EXT4_IO_END_UNWRITTEN; + /* end_io context can not be destroyed now because it still + * used by queued worker. Worker thread will destroy it later */ + if (io->flag & EXT4_IO_END_QUEUED) + list_del_init(&io->list); + else + list_move(&io->list, &to_free); + } + /* If we are called from worker context, it is time to clear queued + * flag, and destroy it's end_io if it was converted already */ + if (work_io) { + work_io->flag &= ~EXT4_IO_END_QUEUED; + if (!(work_io->flag & EXT4_IO_END_UNWRITTEN)) + list_add_tail(&work_io->list, &to_free); } - list_del_init(&io->list); spin_unlock_irqrestore(&ei->i_completed_io_lock, flags); - (void) ext4_end_io_nolock(io); - mutex_unlock(&inode->i_mutex); -free: - ext4_free_io_end(io); + + while (!list_empty(&to_free)) { + io = list_entry(to_free.next, ext4_io_end_t, list); + list_del_init(&io->list); + ext4_free_io_end(io); + } + return ret; +} + +/* + * work on completed aio dio IO, to convert unwritten extents to extents + */ +static void ext4_end_io_work(struct work_struct *work) +{ + ext4_io_end_t *io = container_of(work, ext4_io_end_t, work); + ext4_do_flush_completed_IO(io->inode, io); +} + +int ext4_flush_completed_IO(struct inode *inode) +{ + return ext4_do_flush_completed_IO(inode, NULL); } ext4_io_end_t *ext4_init_io_end(struct inode *inode, gfp_t flags) @@ -199,9 +263,7 @@ static void buffer_io_error(struct buffer_head *bh) static void ext4_end_bio(struct bio *bio, int error) { ext4_io_end_t *io_end = bio->bi_private; - struct workqueue_struct *wq; struct inode *inode; - unsigned long flags; int i; sector_t bi_sector = bio->bi_sector; @@ -259,14 +321,7 @@ static void ext4_end_bio(struct bio *bio, int error) return; } - /* Add the io_end to per-inode completed io list*/ - spin_lock_irqsave(&EXT4_I(inode)->i_completed_io_lock, flags); - list_add_tail(&io_end->list, &EXT4_I(inode)->i_completed_io_list); - spin_unlock_irqrestore(&EXT4_I(inode)->i_completed_io_lock, flags); - - wq = EXT4_SB(inode->i_sb)->dio_unwritten_wq; - /* queue the work to convert unwritten extents to written */ - queue_work(wq, &io_end->work); + ext4_add_complete_io(io_end); } void ext4_io_submit(struct ext4_io_submit *io) -- cgit v1.2.3-59-g8ed1b