Re: [PATCH 6/7] ext4: endless truncate due to nonlocked dio readers V2

  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:

quoted

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 <redacted>
---
 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@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

-- 
Jan Kara [off-list ref]
SUSE Labs, CR