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Date: Sat, 21 Nov 2020 09:55:04 +0800 From: Xiaochen Shen <xiaochen.shen@...el.com> To: Borislav Petkov <bp@...en8.de> 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, Xiaochen Shen <xiaochen.shen@...el.com> Subject: Re: [PATCH 1/3] x86/resctrl: Remove superfluous kernfs_get() calls to prevent refcount leak 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@intel.com The link of the patch series with 3 patches: https://lkml.kernel.org/r/1604084530-31048-1-git-send-email-xiaochen.shen@intel.com 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@...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? Yes. Thank you. -- Best regards, Xiaochen
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