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Message-ID: <CA+FuTSeTu-LUBvewPiM5FFGuEiAvmp-ukdjFn4UvYwTZViCqbg@mail.gmail.com> Date: Fri, 30 Oct 2020 19:31:08 -0400 From: Willem de Bruijn <willemdebruijn.kernel@...il.com> To: Xiaochen Shen <xiaochen.shen@...el.com> Cc: Thomas Gleixner <tglx@...utronix.de>, mingo@...hat.com, bp@...en8.de, HPA <hpa@...or.com>, tony.luck@...el.com, Fenghua Yu <fenghua.yu@...el.com>, Reinette Chatre <reinette.chatre@...el.com>, x86@...nel.org, linux-kernel <linux-kernel@...r.kernel.org>, pei.p.jia@...el.com Subject: Re: [PATCH 1/3] x86/resctrl: Remove superfluous kernfs_get() calls to prevent refcount leak On Fri, Oct 30, 2020 at 2:45 PM Xiaochen Shen <xiaochen.shen@...el.com> 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@...r.kernel.org > 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") > Reported-by: Willem de Bruijn <willemb@...gle.com> > Signed-off-by: Xiaochen Shen <xiaochen.shen@...el.com> > Reviewed-by: Reinette Chatre <reinette.chatre@...el.com> Tested-by: Willem de Bruijn <willemb@...gle.com> This addresses both kernfs_node_cache slab leaks I previously observed. Thanks for fixing these! for i in {1..100000}; do mount -t resctrl resctrl /sys/fs/resctrl; umount /sys/fs/resctrl; done for i in {1..100000}; do mkdir /sys/fs/resctrl/task1; rmdir /sys/fs/resctrl/task1; done
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