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Revert "cgroup: fix race between fork and cgroup.kill"

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This reverts commit 28e51dd4f2 which is
commit b69bb476dee99d564d65d418e9a20acca6f32c3f upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: I679df65c191344d69cdde76cba10b66ba2bf8e1e
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
This commit is contained in:
Greg Kroah-Hartman
2025-03-12 06:05:24 +00:00
parent f082ff3de7
commit 5c2815ea50
3 changed files with 11 additions and 16 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
include/linux/cgroup-defs.h
View File

@@ -71,6 +71,9 @@ enum {
/* Cgroup is frozen. */
CGRP_FROZEN,
/* Control group has to be killed. */
CGRP_KILL,
};
/* cgroup_root->flags */
@@ -421,9 +424,6 @@ struct cgroup {
int nr_threaded_children; /* # of live threaded child cgroups */
/* sequence number for cgroup.kill, serialized by css_set_lock. */
unsigned int kill_seq;
struct kernfs_node *kn; /* cgroup kernfs entry */
struct cgroup_file procs_file; /* handle for "cgroup.procs" */
struct cgroup_file events_file; /* handle for "cgroup.events" */

1
include/linux/sched/task.h
View File

@@ -38,7 +38,6 @@ struct kernel_clone_args {
void *fn_arg;
struct cgroup *cgrp;
struct css_set *cset;
unsigned int kill_seq;
};
/*

20
kernel/cgroup/cgroup.c
View File

@@ -3961,7 +3961,7 @@ static void __cgroup_kill(struct cgroup *cgrp)
lockdep_assert_held(&cgroup_mutex);
spin_lock_irq(&css_set_lock);
cgrp->kill_seq++;
set_bit(CGRP_KILL, &cgrp->flags);
spin_unlock_irq(&css_set_lock);
css_task_iter_start(&cgrp->self, CSS_TASK_ITER_PROCS | CSS_TASK_ITER_THREADED, &it);
@@ -3977,6 +3977,10 @@ static void __cgroup_kill(struct cgroup *cgrp)
send_sig(SIGKILL, task, 0);
}
css_task_iter_end(&it);
spin_lock_irq(&css_set_lock);
clear_bit(CGRP_KILL, &cgrp->flags);
spin_unlock_irq(&css_set_lock);
}
static void cgroup_kill(struct cgroup *cgrp)
@@ -6421,10 +6425,6 @@ static int cgroup_css_set_fork(struct kernel_clone_args *kargs)
spin_lock_irq(&css_set_lock);
cset = task_css_set(current);
get_css_set(cset);
if (kargs->cgrp)
kargs->kill_seq = kargs->cgrp->kill_seq;
else
kargs->kill_seq = cset->dfl_cgrp->kill_seq;
spin_unlock_irq(&css_set_lock);
if (!(kargs->flags & CLONE_INTO_CGROUP)) {
@@ -6608,7 +6608,6 @@ void cgroup_post_fork(struct task_struct *child,
struct kernel_clone_args *kargs)
__releases(&cgroup_threadgroup_rwsem) __releases(&cgroup_mutex)
{
unsigned int cgrp_kill_seq = 0;
unsigned long cgrp_flags = 0;
bool kill = false;
struct cgroup_subsys *ss;
@@ -6622,13 +6621,10 @@ void cgroup_post_fork(struct task_struct *child,
/* init tasks are special, only link regular threads */
if (likely(child->pid)) {
if (kargs->cgrp) {
if (kargs->cgrp)
cgrp_flags = kargs->cgrp->flags;
cgrp_kill_seq = kargs->cgrp->kill_seq;
} else {
else
cgrp_flags = cset->dfl_cgrp->flags;
cgrp_kill_seq = cset->dfl_cgrp->kill_seq;
}
WARN_ON_ONCE(!list_empty(&child->cg_list));
cset->nr_tasks++;
@@ -6663,7 +6659,7 @@ void cgroup_post_fork(struct task_struct *child,
* child down right after we finished preparing it for
* userspace.
*/
kill = kargs->kill_seq != cgrp_kill_seq;
kill = test_bit(CGRP_KILL, &cgrp_flags);
}
spin_unlock_irq(&css_set_lock);