On Thu, 13 Sep 2012 19:01:07 +0400, Dmitry Monakhov <dmonakhov@xxxxxxxxxx> wrote:
> Current unwritten extent conversion state-machine is very fuzzy.
> - By unknown reason it want perform conversion under i_mutex. What for?
> The only reason it used here is just protect io->flags modification,
> but only flush_completed_IO and work modified this flags and
> we can serialize them via i_completed_io_lock.
> All this games with mutex_trylock result in 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
>
> This patch makes state machine simple and clean:
>
> (1) ext4_flush_completed_IO is responsible for handling all pending
> end_io from ei->i_completed_io_list(per inode list)
> NOTE1: i_completed_io_lock is acquired only once
> NOTE2: i_mutex is not required because it does not protect
> any data guarded by i_mutex
>
> (2) xxx_end_io schedule end_io context completion simply by pushing it
> to the inode's list.
> NOTE1: because of (1) work should be queued only if
> ->i_completed_io_list was empty at the moment, otherwise it
> work is scheduled already.
>
> (3) No one is able to free inode's blocks while pented io_completion
> exist othervise may result in blocks beyond EOF.
>
> - remove useless EXT4_IO_END_QUEUED and EXT4_IO_END_FSYNC flags
> - 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.
> - Move open coded logic from various xx_end_xx routines to ext4_add_complete_io()
> - Add BUG_ON to ext_ext_remove_space() in order to assert (3)
>
> Changes since V1:
> Add bugon assertion according to Jan's comment
>
> Reviewed-by: Zheng Liu <wenqing.lz@xxxxxxxxxx>
> Signed-off-by: Dmitry Monakhov <dmonakhov@xxxxxxxxxx>
> ---
> fs/ext4/ext4.h | 5 +--
> fs/ext4/extents.c | 1 +
> fs/ext4/fsync.c | 47 +++++++++++---------------------
> fs/ext4/indirect.c | 6 +---
> fs/ext4/inode.c | 25 +---------------
> fs/ext4/page-io.c | 76 ++++++++++++++-------------------------------------
> 6 files changed, 44 insertions(+), 116 deletions(-)
>
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index b3f3c55..be976ca 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -184,9 +184,7 @@ struct mpage_da_data {
> */
> #define EXT4_IO_END_UNWRITTEN 0x0001
> #define EXT4_IO_END_ERROR 0x0002
> -#define EXT4_IO_END_QUEUED 0x0004
> -#define EXT4_IO_END_DIRECT 0x0008
> -#define EXT4_IO_END_IN_FSYNC 0x0010
> +#define EXT4_IO_END_DIRECT 0x0004
>
> struct ext4_io_page {
> struct page *p_page;
> @@ -2405,6 +2403,7 @@ extern int ext4_move_extents(struct file *o_filp, struct file *d_filp,
>
> /* page-io.c */
> extern int __init ext4_init_pageio(void);
> +extern void ext4_add_complete_io(ext4_io_end_t *io_end);
> extern void ext4_exit_pageio(void);
> extern void ext4_ioend_wait(struct inode *);
> extern void ext4_free_io_end(ext4_io_end_t *io);
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index e993879..44e33b0 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -2618,6 +2618,7 @@ static int ext4_ext_remove_space(struct inode *inode, ext4_lblk_t start,
> handle_t *handle;
> int i = 0, err;
>
> + BUG_ON(atomic_read(&EXT4_I(inode)->i_aiodio_unwritten));
Yeah. I've just triggered this bugon. Even it it is false trigger
because it is safe to have i_aiodio_unwritten some where inside
file while file grow it in progress, but in order to be on the
safe side lets move inode_dio_wait inside ext4_truncate()
so it allow us to have 100% bulletproof assertion
inside ext4_ext_remove_space:
BUG_ON(atomic_read(&EXT4_I(inode)->i_aiodio_unwritten))
BUG_ON(atomic_read(&(inode)->i_dio_count))
This should not affect performance since we already wait for dio tasks
during ext4_setattr, but now we will also will wait on failed_write
which happen only on error path.
EXT4-fs (dm-1): mounted filesystem with ordered data mode. Opts:
acl,user_xattr
------------[ cut here ]------------
kernel BUG at fs/ext4/extents.c:2621!
invalid opcode: 0000 [#1] SMP
Modules linked in: brd ext4 jbd2 cpufreq_ondemand acpi_cpufreq
freq_table mperf coretemp kvm_intel kvm crc32c_intel ghash_clmulni_intel
microcode sg xhci_hcd ext3 jbd mbcache sd_mod crc_t10dif aesni_intel
ablk_helper cryptd aes_x86_64 aes_generic ahci libahci pata_acpi
ata_generic dm_mirror dm_region_hash dm_log dm_mod
CPU 2
Pid: 11079, comm: fio Not tainted 3.6.0-rc1+ #62
/DQ67SW
RIP: 0010:[<ffffffffa0405799>] [<ffffffffa0405799>]
ext4_ext_remove_space+0x79/0xa80 [ext4]
RSP: 0018:ffff8801bcc87888 EFLAGS: 00010202
RAX: 0000000000000003 RBX: ffff88022b7d62c8 RCX: 000000000000000c
RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffffffa0481d90
RBP: ffff8801bcc87938 R08: 0000000000000001 R09: 0000000000000000
R10: ffffffffa04546d8 R11: 0000000000000001 R12: ffff8801ff109000
R13: 00000000fffffffe R14: 000000000026c8d0 R15: 0000000000000001
FS: 00007f4c3dd6a700(0000) GS:ffff88023d800000(0000)
knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f4c34f4f172 CR3: 0000000204d80000 CR4: 00000000000407e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Process fio (pid: 11079, threadinfo ffff8801bcc86000, task
ffff88018f9e5700)
Stack:
ffff88022b7d62c8 0000000000000000 ffff8801f1595cf8 ffff8801d8ff7000
ffff8801bcc87938 ffffffffa03cd363 ffffffffa0408a15 0000000000000000
ffff8801bcc878f8 0000000000000246 ffff88022b7d6238 ffffffffa0408a3d
Call Trace:
[<ffffffffa03cd363>] ? ext4_mark_inode_dirty+0x293/0x2e0 [ext4]
[<ffffffffa0408a15>] ? ext4_ext_truncate+0x115/0x2a0 [ext4]
[<ffffffffa0408a3d>] ? ext4_ext_truncate+0x13d/0x2a0 [ext4]
[<ffffffffa0408a15>] ? ext4_ext_truncate+0x115/0x2a0 [ext4]
[<ffffffffa0408a5e>] ext4_ext_truncate+0x15e/0x2a0 [ext4]
[<ffffffffa03c9e9a>] ext4_truncate+0x14a/0x240 [ext4]
[<ffffffffa04224b1>] ext4_ind_direct_IO+0x481/0x740 [ext4]
[<ffffffffa03cc970>] ? noalloc_get_block_write+0x90/0x90 [ext4]
[<ffffffff81028965>] ? native_sched_clock+0x65/0xb0
[<ffffffffa03c822e>] ext4_ext_direct_IO+0x26e/0x290 [ext4]
[<ffffffffa03c83cc>] ext4_direct_IO+0x17c/0x2a0 [ext4]
[<ffffffff81184354>] generic_file_direct_write+0x174/0x240
[<ffffffff811849d0>] __generic_file_aio_write+0x5b0/0x820
[<ffffffff81028965>] ? native_sched_clock+0x65/0xb0
[<ffffffffa03c1491>] ext4_file_dio_write+0x3b1/0x550 [ext4]
[<ffffffffa03c1778>] ext4_file_write+0x148/0x190 [ext4]
[<ffffffffa03c1630>] ? ext4_file_dio_write+0x550/0x550 [ext4]
[<ffffffff8127532e>] aio_rw_vect_retry+0xce/0x200
[<ffffffff81275260>] ? aio_advance_iovec+0x130/0x130
[<ffffffff81276246>] aio_run_iocb+0xd6/0x2a0
[<ffffffff8173ce1d>] io_submit_one+0x38a/0x3ff
[<ffffffff81277e1e>] do_io_submit+0x2be/0x3d0
[<ffffffff81277f40>] sys_io_submit+0x10/0x20
[<ffffffff8175e4e9>] system_call_fastpath+0x16/0x1b
Code: c7 c7 90 1d 48 a0 85 c0 41 0f 95 c7 31 d2 44 89 fe e8 fc a5 d5 e0
49 63 c7 48 83 c0 02 48 83 04 c5 d0 09 47 a0 01 45 85 ff 74 02 <0f> 0b
0f b7 75 bc 48 8b 7b 28 83 c6 01 e8 65 11 ff ff 48 89 c7
RIP [<ffffffffa0405799>] ext4_ext_remove_space+0x79/0xa80 [ext4]
RSP <ffff8801bcc87888>
---[ end trace 19c3447cad5485fa ]---
>
> /* probably first extent we're gonna free will be last in block */
> diff --git a/fs/ext4/fsync.c b/fs/ext4/fsync.c
> index 323eb15..24f3719 100644
> --- a/fs/ext4/fsync.c
> +++ b/fs/ext4/fsync.c
> @@ -73,46 +73,31 @@ static void dump_completed_IO(struct inode * inode)
> * might needs to do the conversion. This function walks through
> * the list and convert the related unwritten extents for completed IO
> * to written.
> - * The function return the number of pending IOs on success.
> + * The function return first error;
> */
> int ext4_flush_completed_IO(struct inode *inode)
> {
> + struct ext4_inode_info *ei = EXT4_I(inode);
> + unsigned long flags;
> + struct list_head complete_list;
> + int err, ret = 0;
> ext4_io_end_t *io;
> - struct ext4_inode_info *ei = EXT4_I(inode);
> - unsigned long flags;
> - int ret = 0;
> - int ret2 = 0;
>
> dump_completed_IO(inode);
> +
> spin_lock_irqsave(&ei->i_completed_io_lock, flags);
> - while (!list_empty(&ei->i_completed_io_list)){
> - io = list_entry(ei->i_completed_io_list.next,
> - ext4_io_end_t, list);
> + list_replace_init(&ei->i_completed_io_list, &complete_list);
> + spin_unlock_irqrestore(&ei->i_completed_io_lock, flags);
> +
> + while(!list_empty(&complete_list)) {
> + io = list_entry(complete_list.next, ext4_io_end_t, list);
> list_del_init(&io->list);
> - io->flag |= EXT4_IO_END_IN_FSYNC;
> - /*
> - * Calling ext4_end_io_nolock() to convert completed
> - * IO to written.
> - *
> - * When ext4_sync_file() is called, run_queue() may already
> - * about to flush the work corresponding to this io structure.
> - * It will be upset if it founds the io structure related
> - * to the work-to-be schedule is freed.
> - *
> - * Thus we need to keep the io structure still valid here after
> - * conversion finished. The io structure has a flag to
> - * avoid double converting from both fsync and background work
> - * queue work.
> - */
> - spin_unlock_irqrestore(&ei->i_completed_io_lock, flags);
> - ret = ext4_end_io_nolock(io);
> - if (ret < 0)
> - ret2 = ret;
> - spin_lock_irqsave(&ei->i_completed_io_lock, flags);
> - io->flag &= ~EXT4_IO_END_IN_FSYNC;
> + err = ext4_end_io_nolock(io);
> + ext4_free_io_end(io);
> + if (unlikely(err && !ret))
> + ret = err;
> }
> - spin_unlock_irqrestore(&ei->i_completed_io_lock, flags);
> - return (ret2 < 0) ? ret2 : 0;
> + return ret;
> }
>
> /*
> diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c
> index 830e1b2..61f13e5 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,
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 202ae3f..762b955 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -2885,9 +2885,6 @@ static void ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
> {
> struct inode *inode = iocb->ki_filp->f_path.dentry->d_inode;
> ext4_io_end_t *io_end = iocb->private;
> - struct workqueue_struct *wq;
> - unsigned long flags;
> - struct ext4_inode_info *ei;
>
> /* if not async direct IO or dio with 0 bytes write, just return */
> if (!io_end || !size)
> @@ -2916,24 +2913,14 @@ out:
> io_end->iocb = iocb;
> io_end->result = ret;
> }
> - wq = EXT4_SB(io_end->inode->i_sb)->dio_unwritten_wq;
> -
> - /* Add the io_end to per-inode completed aio dio list*/
> - ei = EXT4_I(io_end->inode);
> - spin_lock_irqsave(&ei->i_completed_io_lock, flags);
> - list_add_tail(&io_end->list, &ei->i_completed_io_list);
> - spin_unlock_irqrestore(&ei->i_completed_io_lock, flags);
>
> - /* queue the work to convert unwritten extents to written */
> - queue_work(wq, &io_end->work);
> + ext4_add_complete_io(io_end);
> }
>
> static void ext4_end_io_buffer_write(struct buffer_head *bh, int uptodate)
> {
> ext4_io_end_t *io_end = bh->b_private;
> - struct workqueue_struct *wq;
> struct inode *inode;
> - unsigned long flags;
>
> if (!test_clear_buffer_uninit(bh) || !io_end)
> goto out;
> @@ -2952,15 +2939,7 @@ static void ext4_end_io_buffer_write(struct buffer_head *bh, int uptodate)
> */
> inode = io_end->inode;
> ext4_set_io_unwritten_flag(inode, io_end);
> -
> - /* 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);
> out:
> bh->b_private = NULL;
> bh->b_end_io = NULL;
> diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
> index dcdeef1..c369419 100644
> --- a/fs/ext4/page-io.c
> +++ b/fs/ext4/page-io.c
> @@ -57,6 +57,22 @@ void ext4_ioend_wait(struct inode *inode)
> wait_event(*wq, (atomic_read(&EXT4_I(inode)->i_ioend_count) == 0));
> }
>
> +/* Add the io_end to per-inode completed aio dio list. */
> +void ext4_add_complete_io(ext4_io_end_t *io_end)
> +{
> + struct ext4_inode_info *ei = EXT4_I(io_end->inode);
> + struct workqueue_struct *wq;
> + unsigned long flags;
> +
> + wq = EXT4_SB(io_end->inode->i_sb)->dio_unwritten_wq;
> +
> + spin_lock_irqsave(&ei->i_completed_io_lock, flags);
> + if (list_empty(&ei->i_completed_io_list))
> + 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);
> +}
> +
> static void put_io_page(struct ext4_io_page *io_page)
> {
> if (atomic_dec_and_test(&io_page->p_count)) {
> @@ -81,12 +97,7 @@ 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()
> - */
> +/* check a range of space and convert unwritten extents to written. */
> int ext4_end_io_nolock(ext4_io_end_t *io)
> {
> struct inode *inode = io->inode;
> @@ -94,6 +105,8 @@ int ext4_end_io_nolock(ext4_io_end_t *io)
> ssize_t size = io->size;
> int ret = 0;
>
> + BUG_ON(!list_empty(&io->list));
> +
> 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);
> @@ -124,45 +137,7 @@ int ext4_end_io_nolock(ext4_io_end_t *io)
> static void ext4_end_io_work(struct work_struct *work)
> {
> 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;
> -
> - 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 (!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;
> - }
> - 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);
> + (void) ext4_flush_completed_IO(io->inode);
> }
>
> ext4_io_end_t *ext4_init_io_end(struct inode *inode, gfp_t flags)
> @@ -195,9 +170,7 @@ 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;
>
> @@ -255,14 +228,7 @@ 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)
> --
> 1.7.7.6
>
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