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Merge branch 'for-4.11-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup

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Pull cgroup fixes from Tejun Heo:
 "This contains fixes for two long standing subtle bugs:

   - kthread_bind() on a new kthread binds it to specific CPUs and
     prevents userland from messing with the affinity or cgroup
     membership. Unfortunately, for cgroup membership, there's a window
     between kthread creation and kthread_bind*() invocation where the
     kthread can be moved into a non-root cgroup by userland.

     Depending on what controllers are in effect, this can assign the
     kthread unexpected attributes. For example, in the reported case,
     workqueue workers ended up in a non-root cpuset cgroups and had
     their CPU affinities overridden. This broke workqueue invariants
     and led to workqueue stalls.

     Fixed by closing the window between kthread creation and
     kthread_bind() as suggested by Oleg.

   - There was a bug in cgroup mount path which could allow two
     competing mount attempts to attach the same cgroup_root to two
     different superblocks.

     This was caused by mishandling return value from kernfs_pin_sb().

     Fixed"

* 'for-4.11-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
  cgroup: avoid attaching a cgroup root to two different superblocks
  cgroup, kthread: close race window where new kthreads can be migrated to non-root cgroups
This commit is contained in:
Linus Torvalds
2017-04-11 23:38:16 -07:00
parent af94bdfa79 bfb0b80db5
commit 06ea4c38bc
5 changed files with 34 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
kernel/cgroup/cgroup-v1.c
View File

@@ -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))

9
kernel/cgroup/cgroup.c
View File

@@ -2425,11 +2425,12 @@ ssize_t __cgroup_procs_write(struct kernfs_open_file *of, char *buf,
tsk = tsk->group_leader;
/*
* Workqueue threads may acquire PF_NO_SETAFFINITY and become
* trapped in a cpuset, or RT worker may be born in a cgroup
* with no rt_runtime allocated. Just say no.
* kthreads may acquire PF_NO_SETAFFINITY during initialization.
* If userland migrates such a kthread to a non-root cgroup, it can
* become trapped in a cpuset, or RT kthread may be born in a
* cgroup with no rt_runtime allocated. Just say no.
*/
if (tsk == kthreadd_task || (tsk->flags & PF_NO_SETAFFINITY)) {
if (tsk->no_cgroup_migration || (tsk->flags & PF_NO_SETAFFINITY)) {
ret = -EINVAL;
goto out_unlock_rcu;
}

3
kernel/kthread.c
View File

@@ -20,6 +20,7 @@
#include <linux/freezer.h>
#include <linux/ptrace.h>
#include <linux/uaccess.h>
#include <linux/cgroup.h>
#include <trace/events/sched.h>
static DEFINE_SPINLOCK(kthread_create_lock);
@@ -225,6 +226,7 @@ static int kthread(void *_create)
ret = -EINTR;
if (!test_bit(KTHREAD_SHOULD_STOP, &self->flags)) {
cgroup_kthread_ready();
__kthread_parkme(self);
ret = threadfn(data);
}
@@ -538,6 +540,7 @@ int kthreadd(void *unused)
set_mems_allowed(node_states[N_MEMORY]);
current->flags |= PF_NOFREEZE;
cgroup_init_kthreadd();
for (;;) {
set_current_state(TASK_INTERRUPTIBLE);