Hello, One of our CRIU tests hangs with this patch. Steps to reproduce: curl -o cgroupns.c https://gist.githubusercontent.com/avagin/f87c8a8bd2a0de9afcc74976327786bc/raw/5843701ef3679f50dd2427cf57a80871082eb28c/gistfile1.txt gcc cgroupns.c -o cgroupns ./cgroupns ./cgroupns [root@fc24 ~]# strace -s 256 -fe clone,unshare,setns,mount ./cgroupns mount("none", "/tmp/cgroupns.test/zdtmtst", "cgroup", 0, "none,name=zdtmtst") = 0 unshare(CLONE_NEWCGROUP) = 0 clone(child_stack=NULL, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fe5da0b89d0) = 529 strace: Process 529 attached [pid 529] setns(3, CLONE_NEWCGROUP) = 0 [pid 529] +++ exited with 0 +++ --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=529, si_uid=0, si_status=0, si_utime=0, si_stime=0} --- +++ exited with 0 +++ [root@fc24 ~]# strace -s 256 -fe clone,unshare,setns,mount ./cgroupns mount("none", "/tmp/cgroupns.test/zdtmtst", "cgroup", 0, "none,name=zdtmtst") = ? ERESTARTNOINTR (To be restarted) mount("none", "/tmp/cgroupns.test/zdtmtst", "cgroup", 0, "none,name=zdtmtst") = ? ERESTARTNOINTR (To be restarted) mount("none", "/tmp/cgroupns.test/zdtmtst", "cgroup", 0, "none,name=zdtmtst") = ? ERESTARTNOINTR (To be restarted) mount("none", "/tmp/cgroupns.test/zdtmtst", "cgroup", 0, "none,name=zdtmtst") = ? ERESTARTNOINTR (To be restarted) mount("none", "/tmp/cgroupns.test/zdtmtst", "cgroup", 0, "none,name=zdtmtst") = ? ERESTARTNOINTR (To be restarted) mount("none", "/tmp/cgroupns.test/zdtmtst", "cgroup", 0, "none,name=zdtmtst") = ? ERESTARTNOINTR (To be restarted) .... Thanks, Andrei On Fri, Apr 07, 2017 at 04:51:55PM +0800, Li Zefan wrote: > Run this: > > touch file0 > for ((; ;)) > { > mount -t cpuset xxx file0 > } > > And this concurrently: > > touch file1 > for ((; ;)) > { > mount -t cpuset xxx file1 > } > > We'll trigger a warning like this: > > ------------[ cut here ]------------ > WARNING: CPU: 1 PID: 4675 at lib/percpu-refcount.c:317 percpu_ref_kill_and_confirm+0x92/0xb0 > percpu_ref_kill_and_confirm called more than once on css_release! > CPU: 1 PID: 4675 Comm: mount Not tainted 4.11.0-rc5+ #5 > Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007 > Call Trace: > dump_stack+0x63/0x84 > __warn+0xd1/0xf0 > warn_slowpath_fmt+0x5f/0x80 > percpu_ref_kill_and_confirm+0x92/0xb0 > cgroup_kill_sb+0x95/0xb0 > deactivate_locked_super+0x43/0x70 > deactivate_super+0x46/0x60 > ... > ---[ end trace a79f61c2a2633700 ]--- > > Here's a race: > > Thread A Thread B > > cgroup1_mount() > # alloc a new cgroup root > cgroup_setup_root() > cgroup1_mount() > # no sb yet, returns NULL > kernfs_pin_sb() > > # but succeeds in getting the refcnt, > # so re-use cgroup root > percpu_ref_tryget_live() > # alloc sb with cgroup root > cgroup_do_mount() > > cgroup_kill_sb() > # alloc another sb with same root > cgroup_do_mount() > > cgroup_kill_sb() > > We end up using the same cgroup root for two different superblocks, > so percpu_ref_kill() will be called twice on the same root when the > two superblocks are destroyed. > > We should fix to make sure the superblock pinning is really successful. > > Cc: stable@xxxxxxxxxxxxxxx # 3.16+ > Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> > Signed-off-by: Zefan Li <lizefan@xxxxxxxxxx> > --- > kernel/cgroup/cgroup-v1.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c > index 1dc22f6..12e19f0 100644 > --- a/kernel/cgroup/cgroup-v1.c > +++ b/kernel/cgroup/cgroup-v1.c > @@ -1146,7 +1146,7 @@ struct dentry *cgroup1_mount(struct file_system_type *fs_type, int flags, > * path is super cold. Let's just sleep a bit and retry. > */ > pinned_sb = kernfs_pin_sb(root->kf_root, NULL); > - if (IS_ERR(pinned_sb) || > + if (IS_ERR_OR_NULL(pinned_sb) || > !percpu_ref_tryget_live(&root->cgrp.self.refcnt)) { > mutex_unlock(&cgroup_mutex); > if (!IS_ERR_OR_NULL(pinned_sb)) -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
