From d9c857aee2ebcdf5e9d81718b78b7966b8eee876 Mon Sep 17 00:00:00 2001 From: Pavel Tikhomirov Date: Wed, 18 Mar 2026 13:21:49 +0100 Subject: pid_namespace: avoid optimization of accesses to ->child_reaper 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 Acked-by: Oleg Nesterov Signed-off-by: Pavel Tikhomirov 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 --- kernel/pid.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'kernel/pid.c') diff --git a/kernel/pid.c b/kernel/pid.c index 3b96571d0fe6..386e51fcebb3 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -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)) -- cgit v1.2.3