From mboxrd@z Thu Jan 1 00:00:00 1970 From: Quanyang Wang Subject: Re: [V2][PATCH] cgroup: fix memory leak caused by missing cgroup_bpf_offline Date: Fri, 22 Oct 2021 19:55:50 +0800 Message-ID: <35e9e89f-d92f-06f9-b919-ef956d99d7df@windriver.com> References: <20211018075623.26884-1-quanyang.wang@windriver.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=windriver.com; h=subject : to : cc : references : from : message-id : date : in-reply-to : content-type : content-transfer-encoding : mime-version; s=PPS06212021; bh=wsab649gLJGi//T9euidn7LFas7vqxiCVMXZVelw0Hk=; b=Y0pe9BFIgvOEXDVaPg6DF3ET1J6Tv1QRgyfhSyv6TvzZFvzyCg60erPSmc1EdU7H6mj6 +mcfOUv3iCsAQt52dVx8TKm3iO2S9ye45PE5P+pCvufdgRT2yqzL4EZgHIo5Ic27WmWk dnMfxk/0pPgOwVn3T9A5wu6ev85ytjuKCBm/NCwZBKase8FwziUGQ2YtgCY8621Z7vnX Ghy22ubYvFxMlYSsmCj0wg+XlqSBg+tL7wWQg6iCSak+Enh9hLZo/nX0o2Xaw5h8psYa Y5QnL6ayl8Pf0L0W6sGITFOyff4K8EX6AzXXsmNllGky8xu44hWOyVM8WKb1wZcuCsTo YA== In-Reply-To: Content-Language: en-US List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Roman Gushchin Cc: Tejun Heo , Zefan Li , Johannes Weiner , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Jens Axboe , Ming Lei , mkoutny@suse.com, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org Hi Roman, On 10/22/21 9:30 AM, Roman Gushchin wrote: > On Mon, Oct 18, 2021 at 03:56:23PM +0800, quanyang.wang@windriver.com 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? I ran ltp testsuite to find this. ./runltp -f controllers -s cgroup Thanks, Quanyang > > Anyway, thanks for catching and fixing it! > > Roman >