[3.8.y.z extended stable] Patch "ext4: fix premature freeing of partial clusters split across leaf blocks" has been added to staging queue

[Kamal Mostafa]

On Fri, 2014-04-18 at 17:32 -0400, Eric Whitney wrote:
> * tytso at mit.edu <tytso at mit.edu>:
> > On Fri, Apr 18, 2014 at 10:23:27AM -0700, Kamal Mostafa wrote:
> > > On Thu, 2014-04-17 at 16:30 -0700, Kamal Mostafa wrote:
> > > > This is a note to let you know that I have just added a patch titled
> > > > 
> > > >     ext4: fix premature freeing of partial clusters split across leaf blocks
> > > > 
> > > > to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
> > > 
> > > This patch won't cleanly apply to 3.8 without a prerequisite that has
> > > now been dropped from the queue (ext4: make punch hole code path work
> > > with bigalloc).
> > > 
> > > So this patch (ext4: fix premature freeing) will also be dropped from
> > > the 3.8-stable queue, unless one of the ext4 folks would like to provide
> > > a backport which applies to 3.8-stable's fs/ext4/extents.c[0], or advice
> > > about what that "if partial_cluster" line should look like when all is
> > > said and done.
> > 
> > I believe the problem which this patches is trying to address only
> > happens if punch_hole is enabled for bigalloc. (That is, it should
> > never happen if we are just truncating the file), so this should be
> > OK.
> > 
> > Eric, can you confirm?
> > 
> 
> Dropping this patch from Ubuntu's 3.8 stable queue is fine.  It fixes a bug
> introduced during the 3.10 release cycle that can be triggered by
> truncation as well as hole punching on bigalloc file systems (see d23142c627
> upstream).
> 
> By inspection, the relevant code in 3.8 contains an expression -
> ex >= EXT_FIRST_EXTENT(eh) - that should be equivalent in effect to the one
> added by my patch.  Removal of that expression by d23142c627 caused the bug.
> 
> The xfstests that exposed the bug during 3.14 regression, generic/311 and
> shared/298, did not exist at the time of the 3.8 or 3.10 releases.  I built
> a 3.8 kernel and ran those tests on it - they both passed as expected.
> 
> Please let me know if you have any more questions.
> 
> Eric


Thanks Eric, and thanks again Ted and Lukas.

 -Kamal