bybrooklyn/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-04-18 06:44:00 -04:00
Code Issues Packages Projects Releases Wiki Activity

pid_namespace: avoid optimization of accesses to ->child_reaper

Browse Source 
To avoid potential problems related to cpu/compiler optimizations around
->child_reaper, let's use WRITE_ONCE (additional to task_list lock)
everywhere we write it and use READ_ONCE where we read it without
explicit lock. Note: It also pairs with existing READ_ONCE with no lock
in nsfs_fh_to_dentry().

Also let's add ASSERT_EXCLUSIVE_WRITER before write to identify to KCSAN
that we don't expect any concurrent ->child_reaper modifications, and
those must be detected.

--

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Link: https://patch.msgid.link/20260318122157.280595-2-ptikhomirov@virtuozzo.com
v3: Split from main commit. Add ASSERT_EXCLUSIVE_WRITER.
v5: Add one more READ_ONCE for access without lock in free_pid().
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Pavel Tikhomirov
2026-03-18 13:21:49 +01:00
committed by Christian Brauner
parent 1f318b96cc
commit d9c857aee2
3 changed files with 8 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

3
kernel/exit.c
View File

@@ -608,7 +608,8 @@ static struct task_struct *find_child_reaper(struct task_struct *father,
reaper = find_alive_thread(father);
if (reaper) {
pid_ns->child_reaper = reaper;
ASSERT_EXCLUSIVE_WRITER(pid_ns->child_reaper);
WRITE_ONCE(pid_ns->child_reaper, reaper);
return reaper;
}

5
kernel/fork.c
View File

@@ -2423,7 +2423,10 @@ __latent_entropy struct task_struct *copy_process(
init_task_pid(p, PIDTYPE_SID, task_session(current));
if (is_child_reaper(pid)) {
ns_of_pid(pid)->child_reaper = p;
struct pid_namespace *ns = ns_of_pid(pid);
ASSERT_EXCLUSIVE_WRITER(ns->child_reaper);
WRITE_ONCE(ns->child_reaper, p);
p->signal->flags |= SIGNAL_UNKILLABLE;
}
p->signal->shared_pending.signal = delayed.signal;

4
kernel/pid.c
View File

@@ -128,7 +128,7 @@ void free_pid(struct pid *pid)
* is the reaper wake up the reaper. The reaper
* may be sleeping in zap_pid_ns_processes().
*/
wake_up_process(ns->child_reaper);
wake_up_process(READ_ONCE(ns->child_reaper));
break;
case PIDNS_ADDING:
/* Handle a fork failure of the first process */
@@ -219,7 +219,7 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *arg_set_tid,
* Also fail if a PID != 1 is requested and
* no PID 1 exists.
*/
if (tid != 1 && !tmp->child_reaper)
if (tid != 1 && !READ_ONCE(tmp->child_reaper))
goto out_abort;
retval = -EPERM;
if (!checkpoint_restore_ns_capable(tmp->user_ns))