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Date: Fri, 20 Nov 2020 17:13:51 +0100 From: Borislav Petkov <bp@...en8.de> To: Xiaochen Shen <xiaochen.shen@...el.com> Cc: tglx@...utronix.de, mingo@...hat.com, hpa@...or.com, tony.luck@...el.com, fenghua.yu@...el.com, reinette.chatre@...el.com, willemb@...gle.com, x86@...nel.org, 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 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@...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") Are those 8(!) Fixes tags supposed to list *all* commits which add those wrong kernfs_get() calls? -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette
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