Re: [PATCH 1/3] x86/resctrl: Remove superfluous kernfs_get() calls to prevent refcount leak

[Xiaochen Shen]

Hi Boris,

Thank you very much for code review. More comments are inline.

But I am sorry that I sent this thread by mistake (--in-reply-to a wrong
Message-ID). Please ignore this thread and help review from following
threads:

The link of correct version of this patch [PATCH 1/3]:
https://lkml.kernel.org/r/1604085053-31639-1-git-send-email-xiaochen.shen@xxxxxxxxx

The link of the patch series with 3 patches:
https://lkml.kernel.org/r/1604084530-31048-1-git-send-email-xiaochen.shen@xxxxxxxxx

I am so sorry for the inconvenience.


On 11/21/2020 0:13, Borislav Petkov wrote:
> On Sat, Oct 31, 2020 at 03:03:58AM +0800, Xiaochen Shen wrote:
> > Willem reported growing of kernfs_node_cache entries in slabtop when
> > repeatedly creating and removing resctrl subdirectories as well as when
> > repeatedly mounting and unmounting resctrl filesystem.
> >
> > On resource group (control as well as monitoring) creation via a mkdir
> > an extra kernfs_node reference is obtained to ensure that the rdtgroup
> > structure remains accessible for the rdtgroup_kn_unlock() calls where it
> > is removed on deletion. The kernfs_node reference count is dropped by
> > kernfs_put() in rdtgroup_kn_unlock().
> >
> > With the above explaining the need for one kernfs_get()/kernfs_put()
> > pair in resctrl there are more places where a kernfs_node reference is
> > obtained without a corresponding release. The excessive amount of
> > reference count on kernfs nodes will never be dropped to 0 and the
> > kernfs nodes will never be freed in the call paths of rmdir and umount.
> > It leads to reference count leak and kernfs_node_cache memory leak.
> >
> > Remove the superfluous kernfs_get() calls and expand the existing
> > comments surrounding the remaining kernfs_get()/kernfs_put() pair that
> > remains in use.
> >
> > Superfluous kernfs_get() calls are removed from two areas:
> >
> >    (1) In call paths of mount and mkdir, when kernfs nodes for "info",
> >    "mon_groups" and "mon_data" directories and sub-directories are
> >    created, the reference count of newly created kernfs node is set to 1.
> >    But after kernfs_create_dir() returns, superfluous kernfs_get() are
> >    called to take an additional reference.
> >
> >    (2) kernfs_get() calls in rmdir call paths.
> >
> > Cc: stable@xxxxxxxxxxxxxxx
> > Fixes: 17eafd076291 ("x86/intel_rdt: Split resource group removal in two")
> > Fixes: 4af4a88e0c92 ("x86/intel_rdt/cqm: Add mount,umount support")
> > Fixes: f3cbeacaa06e ("x86/intel_rdt/cqm: Add rmdir support")
> > Fixes: d89b7379015f ("x86/intel_rdt/cqm: Add mon_data")
> > Fixes: c7d9aac61311 ("x86/intel_rdt/cqm: Add mkdir support for RDT monitoring")
> > Fixes: 5dc1d5c6bac2 ("x86/intel_rdt: Simplify info and base file lists")
> > Fixes: 60cf5e101fd4 ("x86/intel_rdt: Add mkdir to resctrl file system")
> > Fixes: 4e978d06dedb ("x86/intel_rdt: Add "info" files to resctrl file system")
> Are those 8(!) Fixes tags supposed to list *all* commits which add those
> wrong kernfs_get() calls?

Yes. Thank you.

--
Best regards,
Xiaochen