Hello,
On Thu 13-09-12 18:41:36, Zheng Liu wrote:
> Could you please provide more detailed workload to convince me? I
> am thinking about whether we really need to disable dioread_nolock
> feature in here. In our benchmarks, we don't see this problem.
I just did:
# Create file
dd if=/dev/zero of=/mnt/file bs=1M count=30
sync
# Start 10 DIO dio readers in parallel reading the file in a loop
for (( i = 0; i < 10; i++ )); do
while true; do
dd if=/mnt/file bs=4k iflag=direct of=/dev/null
done &
done
sleep 1
# Try to truncate the file - never finishes.
truncate -s 16 /mnt/file
It is pretty easy to hit this. Besides being a DOS attack vector (but I
won't be too concerned about this - there are plenty of ways how local
process can screw you) I can easily imagine some application to get bitten
by this.
Honza
>
> Regards,
> Zheng
>
> On Sun, Sep 09, 2012 at 09:27:13PM +0400, Dmitry Monakhov wrote:
> > If we have enough aggressive DIO readers, truncate and other dio
> > waiters will wait forever inside inode_dio_wait(). It is reasonable
> > to disable nonlock DIO read optimization during truncate.
> >
> > Signed-off-by: Dmitry Monakhov <dmonakhov@xxxxxxxxxx>
> > ---
> > fs/ext4/extents.c | 2 +-
> > fs/ext4/fsync.c | 2 +-
> > fs/ext4/inode.c | 2 +-
> > 3 files changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> > index 8252651..b5b801f 100644
> > --- a/fs/ext4/extents.c
> > +++ b/fs/ext4/extents.c
> > @@ -4853,7 +4853,7 @@ int ext4_ext_punch_hole(struct file *file, loff_t offset, loff_t length)
> > }
> >
> > /* finish any pending end_io work */
> > - inode_dio_wait(inode);
> > + ext4_inode_dio_wait(inode, 1);
> > ext4_flush_completed_IO(inode);
> >
> > credits = ext4_writepage_trans_blocks(inode);
> > diff --git a/fs/ext4/fsync.c b/fs/ext4/fsync.c
> > index 290c5cf..bdf6bfd 100644
> > --- a/fs/ext4/fsync.c
> > +++ b/fs/ext4/fsync.c
> > @@ -204,7 +204,7 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
> > if (inode->i_sb->s_flags & MS_RDONLY)
> > goto out;
> >
> > - inode_dio_wait(inode);
> > + ext4_inode_dio_wait(inode, 1);
> > ret = ext4_flush_completed_IO(inode);
> > if (ret < 0)
> > goto out;
> > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> > index 93e6b09..a850026 100644
> > --- a/fs/ext4/inode.c
> > +++ b/fs/ext4/inode.c
> > @@ -4335,7 +4335,7 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
> > truncate_setsize(inode, attr->ia_size);
> > /* Inode size will be reduced, wait for dio in flight */
> > if (orphan)
> > - inode_dio_wait(inode);
> > + ext4_inode_dio_wait(inode, 1);
> > }
> > ext4_truncate(inode);
> > }
> > --
> > 1.7.7.6
> >
> > --
> > To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
> > the body of a message to majordomo@xxxxxxxxxxxxxxx
> > More majordomo info at http://vger.kernel.org/majordomo-info.html
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
