diff mbox series

[3/3] btrfs: Perform locking/unlocking in btrfs_remap_file_range()

Message ID 20190225190744.21664-3-rgoldwyn@suse.de (mailing list archive)
State New, archived
Headers show
Series [1/3] btrfs: Initialize btrfs_io_ctl instead of memsetting it | expand

Commit Message

Goldwyn Rodrigues Feb. 25, 2019, 7:07 p.m. UTC 
From: Goldwyn Rodrigues <rgoldwyn@suse.com>

Moves code to make it more readable, so as locking and unlocking is
done in the same function.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
---
 fs/btrfs/ioctl.c | 53 +++++++++++++++++++++--------------------------------
 1 file changed, 21 insertions(+), 32 deletions(-)

Comments

Filipe Manana Feb. 26, 2019, 12:08 p.m. UTC | #1 
On Mon, Feb 25, 2019 at 7:08 PM Goldwyn Rodrigues <rgoldwyn@suse.de> wrote:
>
> From: Goldwyn Rodrigues <rgoldwyn@suse.com>
>
> Moves code to make it more readable, so as locking and unlocking is
> done in the same function.
>
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
> ---
>  fs/btrfs/ioctl.c | 53 +++++++++++++++++++++--------------------------------
>  1 file changed, 21 insertions(+), 32 deletions(-)
>
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 9c8e1734429c..f0ae1af91ff3 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -3975,22 +3975,6 @@ static int btrfs_remap_file_range_prep(struct file *file_in, loff_t pos_in,
>         u64 wb_len;
>         int ret;
>
> -       if (!(remap_flags & REMAP_FILE_DEDUP)) {
> -               struct btrfs_root *root_out = BTRFS_I(inode_out)->root;
> -
> -               if (btrfs_root_readonly(root_out))xfs_reflink_remap_prep
> -                       return -EROFS;
> -
> -               if (file_in->f_path.mnt != file_out->f_path.mnt ||
> -                   inode_in->i_sb != inode_out->i_sb)
> -                       return -EXDEV;
> -       }

Why move these checks?
The goal of the _prep function (both btrfs and vfs)  is to have the
checks for all needed conditions in one place.

As for the lock/unlock, it follows the same pattern from xfs
(xfs_reflink_remap_prep and xfs_file_remap_range).
No complaints about changing this, I'm just neutral about it.

> -
> -       if (same_inode)
> -               inode_lock(inode_in);
> -       else
> -               btrfs_double_inode_lock(inode_in, inode_out);
> -
>         /*
>          * Now that the inodes are locked, we need to start writeback ourselves
>          * and can not rely on the writeback from the VFS's generic helper
> @@ -4022,26 +4006,14 @@ static int btrfs_remap_file_range_prep(struct file *file_in, loff_t pos_in,
>         ret = btrfs_wait_ordered_range(inode_in, ALIGN_DOWN(pos_in, bs),
>                                        wb_len);
>         if (ret < 0)
> -               goto out_unlock;
> +               return ret;
>         ret = btrfs_wait_ordered_range(inode_out, ALIGN_DOWN(pos_out, bs),
>                                        wb_len);
>         if (ret < 0)
> -               goto out_unlock;
> +               return ret;
>
> -       ret = generic_remap_file_range_prep(file_in, pos_in, file_out, pos_out,
> +       return generic_remap_file_range_prep(file_in, pos_in, file_out, pos_out,
>                                             len, remap_flags);
> -       if (ret < 0 || *len == 0)
> -               goto out_unlock;
> -
> -       return 0;
> -
> - out_unlock:
> -       if (same_inode)
> -               inode_unlock(inode_in);
> -       else
> -               btrfs_double_inode_unlock(inode_in, inode_out);
> -
> -       return ret;
>  }
>
>  loff_t btrfs_remap_file_range(struct file *src_file, loff_t off,
> @@ -4056,16 +4028,33 @@ loff_t btrfs_remap_file_range(struct file *src_file, loff_t off,
>         if (remap_flags & ~(REMAP_FILE_DEDUP | REMAP_FILE_ADVISORY))
>                 return -EINVAL;
>
> +       if (!(remap_flags & REMAP_FILE_DEDUP)) {
> +               struct btrfs_root *root_out = BTRFS_I(dst_inode)->root;
> +
> +               if (btrfs_root_readonly(root_out))
> +                       return -EROFS;
> +
> +               if (src_file->f_path.mnt != dst_file->f_path.mnt ||
> +                   src_inode->i_sb != dst_inode->i_sb)
> +                       return -EXDEV;
> +       }
> +
> +       if (same_inode)
> +               inode_lock(src_inode);
> +       else
> +               btrfs_double_inode_lock(src_inode, dst_inode);
> +
>         ret = btrfs_remap_file_range_prep(src_file, off, dst_file, destoff,
>                                           &len, remap_flags);
>         if (ret < 0 || len == 0)
> -               return ret;
> +               goto out_unlock;
>
>         if (remap_flags & REMAP_FILE_DEDUP)
>                 ret = btrfs_extent_same(src_inode, off, len, dst_inode, destoff);
>         else
>                 ret = btrfs_clone_files(dst_file, src_file, off, len, destoff);
>
> +out_unlock:
>         if (same_inode)
>                 inode_unlock(src_inode);
>         else
> --
> 2.16.4
>
Goldwyn Rodrigues Feb. 26, 2019, 12:57 p.m. UTC | #2 
On 12:08 26/02, Filipe Manana wrote:
> On Mon, Feb 25, 2019 at 7:08 PM Goldwyn Rodrigues <rgoldwyn@suse.de> wrote:
> >
> > From: Goldwyn Rodrigues <rgoldwyn@suse.com>
> >
> > Moves code to make it more readable, so as locking and unlocking is
> > done in the same function.
> >
> > Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
> > ---
> >  fs/btrfs/ioctl.c | 53 +++++++++++++++++++++--------------------------------
> >  1 file changed, 21 insertions(+), 32 deletions(-)
> >
> > diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> > index 9c8e1734429c..f0ae1af91ff3 100644
> > --- a/fs/btrfs/ioctl.c
> > +++ b/fs/btrfs/ioctl.c
> > @@ -3975,22 +3975,6 @@ static int btrfs_remap_file_range_prep(struct file *file_in, loff_t pos_in,
> >         u64 wb_len;
> >         int ret;
> >
> > -       if (!(remap_flags & REMAP_FILE_DEDUP)) {
> > -               struct btrfs_root *root_out = BTRFS_I(inode_out)->root;
> > -
> > -               if (btrfs_root_readonly(root_out))xfs_reflink_remap_prep
> > -                       return -EROFS;
> > -
> > -               if (file_in->f_path.mnt != file_out->f_path.mnt ||
> > -                   inode_in->i_sb != inode_out->i_sb)
> > -                       return -EXDEV;
> > -       }
> 
> Why move these checks?
> The goal of the _prep function (both btrfs and vfs)  is to have the
> checks for all needed conditions in one place.

In the original flow, these checks were done without locks.
But I suppose they can be done with locks held as well.

> 
> As for the lock/unlock, it follows the same pattern from xfs
> (xfs_reflink_remap_prep and xfs_file_remap_range).
> No complaints about changing this, I'm just neutral about it.
> 

I just read the xfs code and yes it is similar. Locking and unlocking
in separate functions makes it difficult to read, especially
when it can be done in the same function.

> > -
> > -       if (same_inode)
> > -               inode_lock(inode_in);
> > -       else
> > -               btrfs_double_inode_lock(inode_in, inode_out);
> > -
> >         /*
> >          * Now that the inodes are locked, we need to start writeback ourselves
> >          * and can not rely on the writeback from the VFS's generic helper
> > @@ -4022,26 +4006,14 @@ static int btrfs_remap_file_range_prep(struct file *file_in, loff_t pos_in,
> >         ret = btrfs_wait_ordered_range(inode_in, ALIGN_DOWN(pos_in, bs),
> >                                        wb_len);
> >         if (ret < 0)
> > -               goto out_unlock;
> > +               return ret;
> >         ret = btrfs_wait_ordered_range(inode_out, ALIGN_DOWN(pos_out, bs),
> >                                        wb_len);
> >         if (ret < 0)
> > -               goto out_unlock;
> > +               return ret;
> >
> > -       ret = generic_remap_file_range_prep(file_in, pos_in, file_out, pos_out,
> > +       return generic_remap_file_range_prep(file_in, pos_in, file_out, pos_out,
> >                                             len, remap_flags);
> > -       if (ret < 0 || *len == 0)
> > -               goto out_unlock;
> > -
> > -       return 0;
> > -
> > - out_unlock:
> > -       if (same_inode)
> > -               inode_unlock(inode_in);
> > -       else
> > -               btrfs_double_inode_unlock(inode_in, inode_out);
> > -
> > -       return ret;
> >  }
> >
> >  loff_t btrfs_remap_file_range(struct file *src_file, loff_t off,
> > @@ -4056,16 +4028,33 @@ loff_t btrfs_remap_file_range(struct file *src_file, loff_t off,
> >         if (remap_flags & ~(REMAP_FILE_DEDUP | REMAP_FILE_ADVISORY))
> >                 return -EINVAL;
> >
> > +       if (!(remap_flags & REMAP_FILE_DEDUP)) {
> > +               struct btrfs_root *root_out = BTRFS_I(dst_inode)->root;
> > +
> > +               if (btrfs_root_readonly(root_out))
> > +                       return -EROFS;
> > +
> > +               if (src_file->f_path.mnt != dst_file->f_path.mnt ||
> > +                   src_inode->i_sb != dst_inode->i_sb)
> > +                       return -EXDEV;
> > +       }
> > +
> > +       if (same_inode)
> > +               inode_lock(src_inode);
> > +       else
> > +               btrfs_double_inode_lock(src_inode, dst_inode);
> > +
> >         ret = btrfs_remap_file_range_prep(src_file, off, dst_file, destoff,
> >                                           &len, remap_flags);
> >         if (ret < 0 || len == 0)
> > -               return ret;
> > +               goto out_unlock;
> >
> >         if (remap_flags & REMAP_FILE_DEDUP)
> >                 ret = btrfs_extent_same(src_inode, off, len, dst_inode, destoff);
> >         else
> >                 ret = btrfs_clone_files(dst_file, src_file, off, len, destoff);
> >
> > +out_unlock:
> >         if (same_inode)
> >                 inode_unlock(src_inode);
> >         else
> > --
> > 2.16.4
> >
> 
> 
> -- 
> Filipe David Manana,
> 
> “Whether you think you can, or you think you can't — you're right.”
>
David Sterba Feb. 27, 2019, 2:52 p.m. UTC | #3 
On Tue, Feb 26, 2019 at 06:57:17AM -0600, Goldwyn Rodrigues wrote:
> On 12:08 26/02, Filipe Manana wrote:
> > On Mon, Feb 25, 2019 at 7:08 PM Goldwyn Rodrigues <rgoldwyn@suse.de> wrote:
> > >
> > > From: Goldwyn Rodrigues <rgoldwyn@suse.com>
> > >
> > > Moves code to make it more readable, so as locking and unlocking is
> > > done in the same function.
> > >
> > > Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
> > > ---
> > >  fs/btrfs/ioctl.c | 53 +++++++++++++++++++++--------------------------------
> > >  1 file changed, 21 insertions(+), 32 deletions(-)
> > >
> > > diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> > > index 9c8e1734429c..f0ae1af91ff3 100644
> > > --- a/fs/btrfs/ioctl.c
> > > +++ b/fs/btrfs/ioctl.c
> > > @@ -3975,22 +3975,6 @@ static int btrfs_remap_file_range_prep(struct file *file_in, loff_t pos_in,
> > >         u64 wb_len;
> > >         int ret;
> > >
> > > -       if (!(remap_flags & REMAP_FILE_DEDUP)) {
> > > -               struct btrfs_root *root_out = BTRFS_I(inode_out)->root;
> > > -
> > > -               if (btrfs_root_readonly(root_out))xfs_reflink_remap_prep
> > > -                       return -EROFS;
> > > -
> > > -               if (file_in->f_path.mnt != file_out->f_path.mnt ||
> > > -                   inode_in->i_sb != inode_out->i_sb)
> > > -                       return -EXDEV;
> > > -       }
> > 
> > Why move these checks?
> > The goal of the _prep function (both btrfs and vfs)  is to have the
> > checks for all needed conditions in one place.
> 
> In the original flow, these checks were done without locks.
> But I suppose they can be done with locks held as well.

The locking does not affect the above checks, so no problem here.

> > 
> > As for the lock/unlock, it follows the same pattern from xfs
> > (xfs_reflink_remap_prep and xfs_file_remap_range).
> > No complaints about changing this, I'm just neutral about it.
> > 
> 
> I just read the xfs code and yes it is similar. Locking and unlocking
> in separate functions makes it difficult to read, especially
> when it can be done in the same function.
> 
> > > -
> > > -       if (same_inode)
> > > -               inode_lock(inode_in);
> > > -       else
> > > -               btrfs_double_inode_lock(inode_in, inode_out);
> > > -

But removing the checks from here can't be done because there's inode
compatibility flag check done right here (in current code, since commit
500710d3b872) but it's not in this diff.

Otherwise there's a race with chatter, once fixed by
b5c40d598f5408bd0ca22dfffa82f03cd9433f23 "Btrfs: fix clone vs chattr
NODATASUM race".
David Sterba Feb. 27, 2019, 3:06 p.m. UTC | #4 
On Wed, Feb 27, 2019 at 03:52:42PM +0100, David Sterba wrote:
> > > > -               struct btrfs_root *root_out = BTRFS_I(inode_out)->root;
> > > > -
> > > > -               if (btrfs_root_readonly(root_out))xfs_reflink_remap_prep
> > > > -                       return -EROFS;
> > > > -
> > > > -               if (file_in->f_path.mnt != file_out->f_path.mnt ||
> > > > -                   inode_in->i_sb != inode_out->i_sb)
> > > > -                       return -EXDEV;
> > > > -       }
> > > 
> > > Why move these checks?
> > > The goal of the _prep function (both btrfs and vfs)  is to have the
> > > checks for all needed conditions in one place.
> > 
> > In the original flow, these checks were done without locks.
> > But I suppose they can be done with locks held as well.
> 
> The locking does not affect the above checks, so no problem here.
> 
> > > 
> > > As for the lock/unlock, it follows the same pattern from xfs
> > > (xfs_reflink_remap_prep and xfs_file_remap_range).
> > > No complaints about changing this, I'm just neutral about it.
> > > 
> > 
> > I just read the xfs code and yes it is similar. Locking and unlocking
> > in separate functions makes it difficult to read, especially
> > when it can be done in the same function.
> > 
> > > > -
> > > > -       if (same_inode)
> > > > -               inode_lock(inode_in);
> > > > -       else
> > > > -               btrfs_double_inode_lock(inode_in, inode_out);
> > > > -
> 
> But removing the checks from here can't be done because there's inode
> compatibility flag check done right here (in current code, since commit
> 500710d3b872) but it's not in this diff.
> 
> Otherwise there's a race with chatter, once fixed by
> b5c40d598f5408bd0ca22dfffa82f03cd9433f23 "Btrfs: fix clone vs chattr
> NODATASUM race".

So the unchecked access to inode flags does not happen, I did not have a
clear picture of the change. The locks are only moved outside of _prep
to the caller.

The lock/unlock look better in the same function, they're close toe each
other on the same page, so ok from me.
David Sterba March 25, 2019, 7:22 p.m. UTC | #5 
On Wed, Feb 27, 2019 at 04:06:24PM +0100, David Sterba wrote:
> So the unchecked access to inode flags does not happen, I did not have a
> clear picture of the change. The locks are only moved outside of _prep
> to the caller.
> 
> The lock/unlock look better in the same function, they're close toe each
> other on the same page, so ok from me.

I've applied the patch and only left the locking changes, as discussed.
diff mbox series

Patch

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 9c8e1734429c..f0ae1af91ff3 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3975,22 +3975,6 @@  static int btrfs_remap_file_range_prep(struct file *file_in, loff_t pos_in,
 	u64 wb_len;
 	int ret;
 
-	if (!(remap_flags & REMAP_FILE_DEDUP)) {
-		struct btrfs_root *root_out = BTRFS_I(inode_out)->root;
-
-		if (btrfs_root_readonly(root_out))
-			return -EROFS;
-
-		if (file_in->f_path.mnt != file_out->f_path.mnt ||
-		    inode_in->i_sb != inode_out->i_sb)
-			return -EXDEV;
-	}
-
-	if (same_inode)
-		inode_lock(inode_in);
-	else
-		btrfs_double_inode_lock(inode_in, inode_out);
-
 	/*
 	 * Now that the inodes are locked, we need to start writeback ourselves
 	 * and can not rely on the writeback from the VFS's generic helper
@@ -4022,26 +4006,14 @@  static int btrfs_remap_file_range_prep(struct file *file_in, loff_t pos_in,
 	ret = btrfs_wait_ordered_range(inode_in, ALIGN_DOWN(pos_in, bs),
 				       wb_len);
 	if (ret < 0)
-		goto out_unlock;
+		return ret;
 	ret = btrfs_wait_ordered_range(inode_out, ALIGN_DOWN(pos_out, bs),
 				       wb_len);
 	if (ret < 0)
-		goto out_unlock;
+		return ret;
 
-	ret = generic_remap_file_range_prep(file_in, pos_in, file_out, pos_out,
+	return generic_remap_file_range_prep(file_in, pos_in, file_out, pos_out,
 					    len, remap_flags);
-	if (ret < 0 || *len == 0)
-		goto out_unlock;
-
-	return 0;
-
- out_unlock:
-	if (same_inode)
-		inode_unlock(inode_in);
-	else
-		btrfs_double_inode_unlock(inode_in, inode_out);
-
-	return ret;
 }
 
 loff_t btrfs_remap_file_range(struct file *src_file, loff_t off,
@@ -4056,16 +4028,33 @@  loff_t btrfs_remap_file_range(struct file *src_file, loff_t off,
 	if (remap_flags & ~(REMAP_FILE_DEDUP | REMAP_FILE_ADVISORY))
 		return -EINVAL;
 
+	if (!(remap_flags & REMAP_FILE_DEDUP)) {
+		struct btrfs_root *root_out = BTRFS_I(dst_inode)->root;
+
+		if (btrfs_root_readonly(root_out))
+			return -EROFS;
+
+		if (src_file->f_path.mnt != dst_file->f_path.mnt ||
+		    src_inode->i_sb != dst_inode->i_sb)
+			return -EXDEV;
+	}
+
+	if (same_inode)
+		inode_lock(src_inode);
+	else
+		btrfs_double_inode_lock(src_inode, dst_inode);
+
 	ret = btrfs_remap_file_range_prep(src_file, off, dst_file, destoff,
 					  &len, remap_flags);
 	if (ret < 0 || len == 0)
-		return ret;
+		goto out_unlock;
 
 	if (remap_flags & REMAP_FILE_DEDUP)
 		ret = btrfs_extent_same(src_inode, off, len, dst_inode, destoff);
 	else
 		ret = btrfs_clone_files(dst_file, src_file, off, len, destoff);
 
+out_unlock:
 	if (same_inode)
 		inode_unlock(src_inode);
 	else