ceph: don't allow copy_file_range when stripe_count != 1
diff mbox series

Message ID 20191031114939.24462-1-lhenriques@suse.com
State New
Headers show
Series
  • ceph: don't allow copy_file_range when stripe_count != 1
Related show

Commit Message

Luis Henriques Oct. 31, 2019, 11:49 a.m. UTC
copy_file_range tries to use the OSD 'copy-from' operation, which simply
performs a full object copy.  Unfortunately, the implementation of this
system call assumes that stripe_count is always set to 1 and doesn't take
into account that the data may be striped across an object set.  If the
file layout has stripe_count different from 1, then the destination file
data will be corrupted.

For example:

Consider a 8 MiB file with 4 MiB object size, stripe_count of 2 and
stripe_size of 2 MiB; the first half of the file will be filled with 'A's
and the second half will be filled with 'B's:

               0      4M     8M       Obj1     Obj2
               +------+------+       +----+   +----+
        file:  | AAAA | BBBB |       | AA |   | AA |
               +------+------+       |----|   |----|
                                     | BB |   | BB |
                                     +----+   +----+

If we copy_file_range this file into a new file (which needs to have the
same file layout!), then it will start by copying the object starting at
file offset 0 (Obj1).  And then it will copy the object starting at file
offset 4M -- which is Obj1 again.

Unfortunately, the solution for this is to not allow remote object copies
to be performed when the file layout stripe_count is not 1 and simply
fallback to the default (VFS) copy_file_range implementation.

Signed-off-by: Luis Henriques <lhenriques@suse.com>
---
Hi Jeff,

I hope my understanding of the whole file striping in CephFS is correct;
I had to go re-read the whole thing to refresh my memory.

Anyway, I guess that this is not really the only solution to this
problem, but it's definitely the simplest one.  copy_file_range is
already way more complex that I had ever anticipated.  I would rather
keep this simple solution instead of adding more complexity and cover
more corner cases.  But yeah, we may want to revisit this in the
future...

[OOT: files layout is probably one of the biggest headaches to sort out
 the day we want to implement something like FIEMAP on CephFS ;-) ]

Cheers,
--
Luis

 fs/ceph/file.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

Comments

Jeff Layton Oct. 31, 2019, 3:28 p.m. UTC | #1
On Thu, 2019-10-31 at 11:49 +0000, Luis Henriques wrote:
> copy_file_range tries to use the OSD 'copy-from' operation, which simply
> performs a full object copy.  Unfortunately, the implementation of this
> system call assumes that stripe_count is always set to 1 and doesn't take
> into account that the data may be striped across an object set.  If the
> file layout has stripe_count different from 1, then the destination file
> data will be corrupted.
> 
> For example:
> 
> Consider a 8 MiB file with 4 MiB object size, stripe_count of 2 and
> stripe_size of 2 MiB; the first half of the file will be filled with 'A's
> and the second half will be filled with 'B's:
> 
>                0      4M     8M       Obj1     Obj2
>                +------+------+       +----+   +----+
>         file:  | AAAA | BBBB |       | AA |   | AA |
>                +------+------+       |----|   |----|
>                                      | BB |   | BB |
>                                      +----+   +----+
> 
> If we copy_file_range this file into a new file (which needs to have the
> same file layout!), then it will start by copying the object starting at
> file offset 0 (Obj1).  And then it will copy the object starting at file
> offset 4M -- which is Obj1 again.
> 
> Unfortunately, the solution for this is to not allow remote object copies
> to be performed when the file layout stripe_count is not 1 and simply
> fallback to the default (VFS) copy_file_range implementation.
> 
> Signed-off-by: Luis Henriques <lhenriques@suse.com>
> ---
> Hi Jeff,
> 
> I hope my understanding of the whole file striping in CephFS is correct;
> I had to go re-read the whole thing to refresh my memory.
> 
> Anyway, I guess that this is not really the only solution to this
> problem, but it's definitely the simplest one.  copy_file_range is
> already way more complex that I had ever anticipated.  I would rather
> keep this simple solution instead of adding more complexity and cover
> more corner cases.  But yeah, we may want to revisit this in the
> future...
> 
> [OOT: files layout is probably one of the biggest headaches to sort out
>  the day we want to implement something like FIEMAP on CephFS ;-) ]
> 
> Cheers,
> --
> Luis
> 
>  fs/ceph/file.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ceph/file.c b/fs/ceph/file.c
> index d277f71abe0b..3b0e6f9eb6a6 100644
> --- a/fs/ceph/file.c
> +++ b/fs/ceph/file.c
> @@ -1957,9 +1957,12 @@ static ssize_t __ceph_copy_file_range(struct file *src_file, loff_t src_off,
>  		return -EOPNOTSUPP;
>  
>  	if ((src_ci->i_layout.stripe_unit != dst_ci->i_layout.stripe_unit) ||
> -	    (src_ci->i_layout.stripe_count != dst_ci->i_layout.stripe_count) ||
> -	    (src_ci->i_layout.object_size != dst_ci->i_layout.object_size))
> +	    (src_ci->i_layout.stripe_count != 1) ||
> +	    (dst_ci->i_layout.stripe_count != 1) ||
> +	    (src_ci->i_layout.object_size != dst_ci->i_layout.object_size)) {
> +		dout("Invalid src/dst files layout\n");
>  		return -EOPNOTSUPP;
> +	}
>  
>  	if (len < src_ci->i_layout.object_size)
>  		return -EOPNOTSUPP; /* no remote copy will be done */

I'm fine with restricting CFR to very simple cases, at least initially.
We can always expand it later once the need becomes clear.

That said, we should probably add a comment explaining why we're
excluding cases where the stripe count != 1 here. It doesn't need to
contain the whole commit log message you wrote, but anyone that does
want to improve this later might appreciate some breadcrumbs.

Maybe something like:

/*
 * Striped file layouts require that we copy partial objects,
 * but the OSD copy-from operation only supports full-object copies.
 * Limit this to non-striped file layouts for now.
 */

If that sounds ok, I'll add that in and merge this later today.

Thanks,
Luis Henriques Oct. 31, 2019, 3:44 p.m. UTC | #2
On Thu, Oct 31, 2019 at 11:28:55AM -0400, Jeff Layton wrote:
> On Thu, 2019-10-31 at 11:49 +0000, Luis Henriques wrote:
> > copy_file_range tries to use the OSD 'copy-from' operation, which simply
> > performs a full object copy.  Unfortunately, the implementation of this
> > system call assumes that stripe_count is always set to 1 and doesn't take
> > into account that the data may be striped across an object set.  If the
> > file layout has stripe_count different from 1, then the destination file
> > data will be corrupted.
> > 
> > For example:
> > 
> > Consider a 8 MiB file with 4 MiB object size, stripe_count of 2 and
> > stripe_size of 2 MiB; the first half of the file will be filled with 'A's
> > and the second half will be filled with 'B's:
> > 
> >                0      4M     8M       Obj1     Obj2
> >                +------+------+       +----+   +----+
> >         file:  | AAAA | BBBB |       | AA |   | AA |
> >                +------+------+       |----|   |----|
> >                                      | BB |   | BB |
> >                                      +----+   +----+
> > 
> > If we copy_file_range this file into a new file (which needs to have the
> > same file layout!), then it will start by copying the object starting at
> > file offset 0 (Obj1).  And then it will copy the object starting at file
> > offset 4M -- which is Obj1 again.
> > 
> > Unfortunately, the solution for this is to not allow remote object copies
> > to be performed when the file layout stripe_count is not 1 and simply
> > fallback to the default (VFS) copy_file_range implementation.
> > 
> > Signed-off-by: Luis Henriques <lhenriques@suse.com>
> > ---
> > Hi Jeff,
> > 
> > I hope my understanding of the whole file striping in CephFS is correct;
> > I had to go re-read the whole thing to refresh my memory.
> > 
> > Anyway, I guess that this is not really the only solution to this
> > problem, but it's definitely the simplest one.  copy_file_range is
> > already way more complex that I had ever anticipated.  I would rather
> > keep this simple solution instead of adding more complexity and cover
> > more corner cases.  But yeah, we may want to revisit this in the
> > future...
> > 
> > [OOT: files layout is probably one of the biggest headaches to sort out
> >  the day we want to implement something like FIEMAP on CephFS ;-) ]
> > 
> > Cheers,
> > --
> > Luis
> > 
> >  fs/ceph/file.c | 7 +++++--
> >  1 file changed, 5 insertions(+), 2 deletions(-)
> > 
> > diff --git a/fs/ceph/file.c b/fs/ceph/file.c
> > index d277f71abe0b..3b0e6f9eb6a6 100644
> > --- a/fs/ceph/file.c
> > +++ b/fs/ceph/file.c
> > @@ -1957,9 +1957,12 @@ static ssize_t __ceph_copy_file_range(struct file *src_file, loff_t src_off,
> >  		return -EOPNOTSUPP;
> >  
> >  	if ((src_ci->i_layout.stripe_unit != dst_ci->i_layout.stripe_unit) ||
> > -	    (src_ci->i_layout.stripe_count != dst_ci->i_layout.stripe_count) ||
> > -	    (src_ci->i_layout.object_size != dst_ci->i_layout.object_size))
> > +	    (src_ci->i_layout.stripe_count != 1) ||
> > +	    (dst_ci->i_layout.stripe_count != 1) ||
> > +	    (src_ci->i_layout.object_size != dst_ci->i_layout.object_size)) {
> > +		dout("Invalid src/dst files layout\n");
> >  		return -EOPNOTSUPP;
> > +	}
> >  
> >  	if (len < src_ci->i_layout.object_size)
> >  		return -EOPNOTSUPP; /* no remote copy will be done */
> 
> I'm fine with restricting CFR to very simple cases, at least initially.
> We can always expand it later once the need becomes clear.
> 
> That said, we should probably add a comment explaining why we're
> excluding cases where the stripe count != 1 here. It doesn't need to
> contain the whole commit log message you wrote, but anyone that does
> want to improve this later might appreciate some breadcrumbs.
> 
> Maybe something like:
> 
> /*
>  * Striped file layouts require that we copy partial objects,
>  * but the OSD copy-from operation only supports full-object copies.
>  * Limit this to non-striped file layouts for now.
>  */
> 
> If that sounds ok, I'll add that in and merge this later today.

Thanks, that looks good to me, feel free to add that comment.

Cheers,
--
Luís
Jeff Layton Oct. 31, 2019, 4:59 p.m. UTC | #3
On Thu, 2019-10-31 at 15:44 +0000, Luis Henriques wrote:
> On Thu, Oct 31, 2019 at 11:28:55AM -0400, Jeff Layton wrote:
> > On Thu, 2019-10-31 at 11:49 +0000, Luis Henriques wrote:
> > > copy_file_range tries to use the OSD 'copy-from' operation, which simply
> > > performs a full object copy.  Unfortunately, the implementation of this
> > > system call assumes that stripe_count is always set to 1 and doesn't take
> > > into account that the data may be striped across an object set.  If the
> > > file layout has stripe_count different from 1, then the destination file
> > > data will be corrupted.
> > > 
> > > For example:
> > > 
> > > Consider a 8 MiB file with 4 MiB object size, stripe_count of 2 and
> > > stripe_size of 2 MiB; the first half of the file will be filled with 'A's
> > > and the second half will be filled with 'B's:
> > > 
> > >                0      4M     8M       Obj1     Obj2
> > >                +------+------+       +----+   +----+
> > >         file:  | AAAA | BBBB |       | AA |   | AA |
> > >                +------+------+       |----|   |----|
> > >                                      | BB |   | BB |
> > >                                      +----+   +----+
> > > 
> > > If we copy_file_range this file into a new file (which needs to have the
> > > same file layout!), then it will start by copying the object starting at
> > > file offset 0 (Obj1).  And then it will copy the object starting at file
> > > offset 4M -- which is Obj1 again.
> > > 
> > > Unfortunately, the solution for this is to not allow remote object copies
> > > to be performed when the file layout stripe_count is not 1 and simply
> > > fallback to the default (VFS) copy_file_range implementation.
> > > 
> > > Signed-off-by: Luis Henriques <lhenriques@suse.com>
> > > ---
> > > Hi Jeff,
> > > 
> > > I hope my understanding of the whole file striping in CephFS is correct;
> > > I had to go re-read the whole thing to refresh my memory.
> > > 
> > > Anyway, I guess that this is not really the only solution to this
> > > problem, but it's definitely the simplest one.  copy_file_range is
> > > already way more complex that I had ever anticipated.  I would rather
> > > keep this simple solution instead of adding more complexity and cover
> > > more corner cases.  But yeah, we may want to revisit this in the
> > > future...
> > > 
> > > [OOT: files layout is probably one of the biggest headaches to sort out
> > >  the day we want to implement something like FIEMAP on CephFS ;-) ]
> > > 
> > > Cheers,
> > > --
> > > Luis
> > > 
> > >  fs/ceph/file.c | 7 +++++--
> > >  1 file changed, 5 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/fs/ceph/file.c b/fs/ceph/file.c
> > > index d277f71abe0b..3b0e6f9eb6a6 100644
> > > --- a/fs/ceph/file.c
> > > +++ b/fs/ceph/file.c
> > > @@ -1957,9 +1957,12 @@ static ssize_t __ceph_copy_file_range(struct file *src_file, loff_t src_off,
> > >  		return -EOPNOTSUPP;
> > >  
> > >  	if ((src_ci->i_layout.stripe_unit != dst_ci->i_layout.stripe_unit) ||
> > > -	    (src_ci->i_layout.stripe_count != dst_ci->i_layout.stripe_count) ||
> > > -	    (src_ci->i_layout.object_size != dst_ci->i_layout.object_size))
> > > +	    (src_ci->i_layout.stripe_count != 1) ||
> > > +	    (dst_ci->i_layout.stripe_count != 1) ||
> > > +	    (src_ci->i_layout.object_size != dst_ci->i_layout.object_size)) {
> > > +		dout("Invalid src/dst files layout\n");
> > >  		return -EOPNOTSUPP;
> > > +	}
> > >  
> > >  	if (len < src_ci->i_layout.object_size)
> > >  		return -EOPNOTSUPP; /* no remote copy will be done */
> > 
> > I'm fine with restricting CFR to very simple cases, at least initially.
> > We can always expand it later once the need becomes clear.
> > 
> > That said, we should probably add a comment explaining why we're
> > excluding cases where the stripe count != 1 here. It doesn't need to
> > contain the whole commit log message you wrote, but anyone that does
> > want to improve this later might appreciate some breadcrumbs.
> > 
> > Maybe something like:
> > 
> > /*
> >  * Striped file layouts require that we copy partial objects,
> >  * but the OSD copy-from operation only supports full-object copies.
> >  * Limit this to non-striped file layouts for now.
> >  */
> > 
> > If that sounds ok, I'll add that in and merge this later today.
> 
> Thanks, that looks good to me, feel free to add that comment.
> 

Merged, and I also marked this for stable, since it's a potential data corruption bug.

Thanks,

Patch
diff mbox series

diff --git a/fs/ceph/file.c b/fs/ceph/file.c
index d277f71abe0b..3b0e6f9eb6a6 100644
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -1957,9 +1957,12 @@  static ssize_t __ceph_copy_file_range(struct file *src_file, loff_t src_off,
 		return -EOPNOTSUPP;
 
 	if ((src_ci->i_layout.stripe_unit != dst_ci->i_layout.stripe_unit) ||
-	    (src_ci->i_layout.stripe_count != dst_ci->i_layout.stripe_count) ||
-	    (src_ci->i_layout.object_size != dst_ci->i_layout.object_size))
+	    (src_ci->i_layout.stripe_count != 1) ||
+	    (dst_ci->i_layout.stripe_count != 1) ||
+	    (src_ci->i_layout.object_size != dst_ci->i_layout.object_size)) {
+		dout("Invalid src/dst files layout\n");
 		return -EOPNOTSUPP;
+	}
 
 	if (len < src_ci->i_layout.object_size)
 		return -EOPNOTSUPP; /* no remote copy will be done */