On Thursday 27 Aug 2015 19:09:44 Liu Bo wrote:
> On Mon, Aug 24, 2015 at 05:34:17PM +0530, Chandan Rajendra wrote:
> > The following call trace is seen when generic/095 test is executed,
> >
> > WARNING: CPU: 3 PID: 2769 at
> > /home/chandan/code/repos/linux/fs/btrfs/inode.c:8967
> > btrfs_destroy_inode+0x284/0x2a0() Modules linked in:
> > CPU: 3 PID: 2769 Comm: umount Not tainted 4.2.0-rc5+ #31
> > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> > 1.7.5-20150306_163512-brownie 04/01/2014>
> > ffffffff81c08150 ffff8802ec9cbce8 ffffffff81984058 ffff8802ffd8feb0
> > 0000000000000000 ffff8802ec9cbd28 ffffffff81050385 ffff8802ec9cbd38
> > ffff8802d12f8588 ffff8802d12f8588 ffff8802f15ab000 ffff8800bb96c0b0
> >
> > Call Trace:
> > [<ffffffff81984058>] dump_stack+0x45/0x57
> > [<ffffffff81050385>] warn_slowpath_common+0x85/0xc0
> > [<ffffffff81050465>] warn_slowpath_null+0x15/0x20
> > [<ffffffff81340294>] btrfs_destroy_inode+0x284/0x2a0
> > [<ffffffff8117ce07>] destroy_inode+0x37/0x60
> > [<ffffffff8117cf39>] evict+0x109/0x170
> > [<ffffffff8117cfd5>] dispose_list+0x35/0x50
> > [<ffffffff8117dd3a>] evict_inodes+0xaa/0x100
> > [<ffffffff81165667>] generic_shutdown_super+0x47/0xf0
> > [<ffffffff81165951>] kill_anon_super+0x11/0x20
> > [<ffffffff81302093>] btrfs_kill_super+0x13/0x110
> > [<ffffffff81165c99>] deactivate_locked_super+0x39/0x70
> > [<ffffffff811660cf>] deactivate_super+0x5f/0x70
> > [<ffffffff81180e1e>] cleanup_mnt+0x3e/0x90
> > [<ffffffff81180ebd>] __cleanup_mnt+0xd/0x10
> > [<ffffffff81069c06>] task_work_run+0x96/0xb0
> > [<ffffffff81003a3d>] do_notify_resume+0x3d/0x50
> > [<ffffffff8198cbc2>] int_signal+0x12/0x17
> >
> > This means that the inode had non-zero "outstanding extents" during
> > eviction. This occurs because during direct I/O, a task which successfully
> > used up its reserved data space would set BTRFS_INODE_DIO_READY bit and
> > does not clear the bit after finishing the DIO write. A future DIO write
> > could actually fail and the unused reserve space won't be freed because
> > of the previously set BTRFS_INODE_DIO_READY bit.
> >
> > Clearing the BTRFS_INODE_DIO_READY bit in btrfs_direct_IO() caused another
> > issue to pop up. In do_direct_IO(), get_more_blocks() could allocate an
> > ordered extent that would partially map the originally requested length.
> > Here we would have set the BTRFS_INODE_DIO_READY bit. While processing
> > the remaining data to be written, dio_get_page() could return with
> > -EFAULT (assume sdio->blocks_availlable had a value of zero). With
> > -EFAULT as the return value from __blockdev_direct_IO(), btrfs_direct_IO
> > would fail to release the rest of unused "reserve space" because
> > BTRFS_INODE_DIO_READY was already set.
> >
> > Hence this commit introduces "struct btrfs_dio_data" to track the usage of
> > reserved data space. The remaining unused "reserve space" can now be freed
> > reliably.
>
> Hi,
>
> Thanks for fixing it, the patch looks good, a runtime flag is global
> and overwrite in direct write does not hold inode->mutex, so we'll get
> into trouble if multiple overwrites are running together.
>
> However, I'm not sure if the above commit log is right, have you ever
> hitten the situation that get_more_blocks() allocates an ordered extent
> that partially maps the requested length?
>
Hello Liu,
I had sprinkled some trace_printk() statements to figure out the behaviour and
did not pay attention to the PIDs printed in the output log. Hence I had come
to the conclusion described in the commit log. Sorry about the incorrect
description.
The following describes the actual behaviour,
|-----------------------------------+-------------------------------------|
| Task A | Task B |
|-----------------------------------+-------------------------------------|
| Start direct i/o write on inode X | |
| reserve space | |
| Allocate ordered extent | |
| release reserved space | |
| Set BTRFS_INODE_DIO_READY bit | |
| | Start direct i/o write on inode X |
| | reserve space |
| | dio_refill_pages() |
| | - sdio->blocks_available == 0 |
| | - Return -EFAULT |
| | Since BTRFS_INODE_DIO_READY is set, |
| | we don't release reserved space. |
| | Clear BTRFS_INODE_DIO_READY bit. |
| -EIOCBQUEUED is returned. | |
|-----------------------------------+-------------------------------------|
I will update the commit log and send version V2. Thanks to you for reviewing
the patch.
> Actually I did a bit debugging, and on my box, it's splice(2) and
> vmsplice(2) that will definitely lead directIO's dio_get_page() to
> return a -EFAULT because the buffer used in splice is in kernel
> address but is acquiring to allocate memory from userspace, so in this
> case, it wouldn't get a chance to run get_more_blocks().
>
> I was just wondering if this also happened on your box?
>
> Thanks,
>
> -liubo
>
> > Signed-off-by: Chandan Rajendra <chan...@linux.vnet.ibm.com>
> > ---
> >
> > fs/btrfs/btrfs_inode.h | 2 --
> > fs/btrfs/inode.c | 42 +++++++++++++++++++++---------------------
> > 2 files changed, 21 insertions(+), 23 deletions(-)
> >
> > diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
> > index 81220b2..0ef5cc1 100644
> > --- a/fs/btrfs/btrfs_inode.h
> > +++ b/fs/btrfs/btrfs_inode.h
> > @@ -44,8 +44,6 @@
> >
> > #define BTRFS_INODE_IN_DELALLOC_LIST 9
> > #define BTRFS_INODE_READDIO_NEED_LOCK 10
> > #define BTRFS_INODE_HAS_PROPS 11
> >
> > -/* DIO is ready to submit */
> > -#define BTRFS_INODE_DIO_READY 12
> >
> > /*
> >
> > * The following 3 bits are meant only for the btree inode.
> > * When any of them is set, it means an error happened while writing an
> >
> > diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> > index bda3c41..83571603 100644
> > --- a/fs/btrfs/inode.c
> > +++ b/fs/btrfs/inode.c
> > @@ -7405,6 +7405,10 @@ static struct extent_map *create_pinned_em(struct
> > inode *inode, u64 start,>
> > return em;
> >
> > }
> >
> > +struct btrfs_dio_data {
> > + u64 outstanding_extents;
> > + u64 reserve;
> > +};
> >
> > static int btrfs_get_blocks_direct(struct inode *inode, sector_t iblock,
> >
> > struct buffer_head *bh_result, int create)
> >
> > @@ -7412,10 +7416,10 @@ static int btrfs_get_blocks_direct(struct inode
> > *inode, sector_t iblock,>
> > struct extent_map *em;
> > struct btrfs_root *root = BTRFS_I(inode)->root;
> > struct extent_state *cached_state = NULL;
> >
> > + struct btrfs_dio_data *dio_data = NULL;
> >
> > u64 start = iblock << inode->i_blkbits;
> > u64 lockstart, lockend;
> > u64 len = bh_result->b_size;
> >
> > - u64 *outstanding_extents = NULL;
> >
> > int unlock_bits = EXTENT_LOCKED;
> > int ret = 0;
> >
> > @@ -7433,7 +7437,7 @@ static int btrfs_get_blocks_direct(struct inode
> > *inode, sector_t iblock,>
> > * that anything that needs to check if there's a transction
doesn't
> > get
> > * confused.
> > */
> >
> > - outstanding_extents = current->journal_info;
> > + dio_data = current->journal_info;
> >
> > current->journal_info = NULL;
> >
> > }
> >
> > @@ -7565,17 +7569,18 @@ unlock:
> > * within our reservation, otherwise we need to adjust our
inode
> > * counter appropriately.
> > */
> >
> > - if (*outstanding_extents) {
> > - (*outstanding_extents)--;
> > + if (dio_data->outstanding_extents) {
> > + (dio_data->outstanding_extents)--;
> >
> > } else {
> >
> > spin_lock(&BTRFS_I(inode)->lock);
> > BTRFS_I(inode)->outstanding_extents++;
> > spin_unlock(&BTRFS_I(inode)->lock);
> >
> > }
> >
> > - current->journal_info = outstanding_extents;
> >
> > btrfs_free_reserved_data_space(inode, len);
> >
> > - set_bit(BTRFS_INODE_DIO_READY, &BTRFS_I(inode)-
>runtime_flags);
> > + WARN_ON(dio_data->reserve < len);
> > + dio_data->reserve -= len;
> > + current->journal_info = dio_data;
> >
> > }
> >
> > /*
> >
> > @@ -7598,8 +7603,8 @@ unlock:
> > unlock_err:
> > clear_extent_bit(&BTRFS_I(inode)->io_tree, lockstart, lockend,
> >
> > unlock_bits, 1, 0, &cached_state, GFP_NOFS);
> >
> > - if (outstanding_extents)
> > - current->journal_info = outstanding_extents;
> > + if (dio_data)
> > + current->journal_info = dio_data;
> >
> > return ret;
> >
> > }
> >
> > @@ -8329,7 +8334,8 @@ static ssize_t btrfs_direct_IO(struct kiocb *iocb,
> > struct iov_iter *iter,>
> > {
> >
> > struct file *file = iocb->ki_filp;
> > struct inode *inode = file->f_mapping->host;
> >
> > - u64 outstanding_extents = 0;
> > + struct btrfs_root *root = BTRFS_I(inode)->root;
> > + struct btrfs_dio_data dio_data = { 0 };
> >
> > size_t count = 0;
> > int flags = 0;
> > bool wakeup = true;
> >
> > @@ -8367,7 +8373,7 @@ static ssize_t btrfs_direct_IO(struct kiocb *iocb,
> > struct iov_iter *iter,>
> > ret = btrfs_delalloc_reserve_space(inode, count);
> > if (ret)
> >
> > goto out;
> >
> > - outstanding_extents = div64_u64(count +
> > + dio_data.outstanding_extents = div64_u64(count +
> >
> > BTRFS_MAX_EXTENT_SIZE - 1,
> > BTRFS_MAX_EXTENT_SIZE);
> >
> > @@ -8376,7 +8382,8 @@ static ssize_t btrfs_direct_IO(struct kiocb *iocb,
> > struct iov_iter *iter,>
> > * do the accounting properly if we go over the number we
> > * originally calculated. Abuse current->journal_info for
this.
> > */
> >
> > - current->journal_info = &outstanding_extents;
> > + dio_data.reserve = round_up(count, root->sectorsize);
> > + current->journal_info = &dio_data;
> >
> > } else if (test_bit(BTRFS_INODE_READDIO_NEED_LOCK,
> >
> > &BTRFS_I(inode)->runtime_flags)) {
> >
> > inode_dio_end(inode);
> >
> > @@ -8391,16 +8398,9 @@ static ssize_t btrfs_direct_IO(struct kiocb *iocb,
> > struct iov_iter *iter,>
> > if (iov_iter_rw(iter) == WRITE) {
> >
> > current->journal_info = NULL;
> > if (ret < 0 && ret != -EIOCBQUEUED) {
> >
> > - /*
> > - * If the error comes from submitting stage,
> > - * btrfs_get_blocsk_direct() has free'd data space,
> > - * and metadata space will be handled by
> > - * finish_ordered_fn, don't do that again to make
> > - * sure bytes_may_use is correct.
> > - */
> > - if (!test_and_clear_bit(BTRFS_INODE_DIO_READY,
> > - &BTRFS_I(inode)->runtime_flags))
> > - btrfs_delalloc_release_space(inode, count);
> > + if (dio_data.reserve)
> > + btrfs_delalloc_release_space(inode,
> > + dio_data.reserve);
> >
> > } else if (ret >= 0 && (size_t)ret < count)
> >
> > btrfs_delalloc_release_space(inode,
> >
> > count - (size_t)ret);
--
chandan
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