From mboxrd@z Thu Jan 1 00:00:00 1970 From: Roman Gushchin Subject: Re: [V2][PATCH] cgroup: fix memory leak caused by missing cgroup_bpf_offline Date: Thu, 21 Oct 2021 18:30:24 -0700 Message-ID: References: <20211018075623.26884-1-quanyang.wang@windriver.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.com; h=date : from : to : cc : subject : message-id : references : content-type : in-reply-to : mime-version; s=facebook; bh=ZAI4ALD3IOPkn/ZDv37bBcofWD94RVNJhCNAaLserkY=; b=BrffFq0QvdYXJy+HxkHv0ZIPDi9j6kg74RNMLpiG70tGCk/HmQCUQwYzwOjKeFrDgl3V ZIVpOyZ7BmjjGar/4aVr73medsuvqwoqBxQLIQyrKwbt3NqPEv57uKLzyKtSqzDRlHS0 Rv+VCrOq/rYYjXU6G83miRIITzyhX8p8FXY= Content-Disposition: inline In-Reply-To: <20211018075623.26884-1-quanyang.wang-CWA4WttNNZF54TAoqtyWWQ@public.gmane.org> List-ID: Content-Transfer-Encoding: 7bit To: quanyang.wang-CWA4WttNNZF54TAoqtyWWQ@public.gmane.org Cc: Tejun Heo , Zefan Li , Johannes Weiner , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Jens Axboe , Ming Lei , mkoutny-IBi9RG/b67k@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, bpf-u79uwXL29TY76Z2rM5mHXA@public.gmane.org On Mon, Oct 18, 2021 at 03:56:23PM +0800, quanyang.wang-CWA4WttNNZF54TAoqtyWWQ@public.gmane.org wrote: > From: Quanyang Wang > > When enabling CONFIG_CGROUP_BPF, kmemleak can be observed by running > the command as below: > > $mount -t cgroup -o none,name=foo cgroup cgroup/ > $umount cgroup/ > > unreferenced object 0xc3585c40 (size 64): > comm "mount", pid 425, jiffies 4294959825 (age 31.990s) > hex dump (first 32 bytes): > 01 00 00 80 84 8c 28 c0 00 00 00 00 00 00 00 00 ......(......... > 00 00 00 00 00 00 00 00 6c 43 a0 c3 00 00 00 00 ........lC...... > backtrace: > [] cgroup_bpf_inherit+0x44/0x24c > [<1f03679c>] cgroup_setup_root+0x174/0x37c > [] cgroup1_get_tree+0x2c0/0x4a0 > [] vfs_get_tree+0x24/0x108 > [] path_mount+0x384/0x988 > [] do_mount+0x64/0x9c > [<208c9cfe>] sys_mount+0xfc/0x1f4 > [<06dd06e0>] ret_fast_syscall+0x0/0x48 > [] 0xbeb4daa8 > > This is because that since the commit 2b0d3d3e4fcf ("percpu_ref: reduce > memory footprint of percpu_ref in fast path") root_cgrp->bpf.refcnt.data > is allocated by the function percpu_ref_init in cgroup_bpf_inherit which > is called by cgroup_setup_root when mounting, but not freed along with > root_cgrp when umounting. Adding cgroup_bpf_offline which calls > percpu_ref_kill to cgroup_kill_sb can free root_cgrp->bpf.refcnt.data in > umount path. > > This patch also fixes the commit 4bfc0bb2c60e ("bpf: decouple the lifetime > of cgroup_bpf from cgroup itself"). A cgroup_bpf_offline is needed to do a > cleanup that frees the resources which are allocated by cgroup_bpf_inherit > in cgroup_setup_root. > > And inside cgroup_bpf_offline, cgroup_get() is at the beginning and > cgroup_put is at the end of cgroup_bpf_release which is called by > cgroup_bpf_offline. So cgroup_bpf_offline can keep the balance of > cgroup's refcount. > > Fixes: 2b0d3d3e4fcf ("percpu_ref: reduce memory footprint of percpu_ref in fast path") > Fixes: 4bfc0bb2c60e ("bpf: decouple the lifetime of cgroup_bpf from cgroup itself") > Signed-off-by: Quanyang Wang > --- > V1 ---> V2: > 1. As per Daniel's suggestion, add description to commit msg about the > balance of cgroup's refcount in cgroup_bpf_offline. > 2. As per Michal's suggestion, add tag "Fixes: 4bfc0bb2c60e" and add > description about it. > 3. Fix indentation on the percpu_ref_is_dying line. Acked-by: Roman Gushchin The fix looks correct, two fixes tag are fine too, if only it won't confuse scripts picking up patches for stable backports. In fact, it's a very cold path, which is arguably never hit in the real life. On cgroup v2 it's not an issue. I'm not sure we need a stable backport at all, only if it creates a noise for some automation tests. Quanyang, out of curiosity, how did you find it? Anyway, thanks for catching and fixing it! Roman