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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 Signed-off-by: Pavel Tikhomirov -- v3: Split from main commit. Add ASSERT_EXCLUSIVE_WRITER. --- kernel/exit.c | 3 ++- kernel/fork.c | 5 ++++- kernel/pid.c | 2 +- 3 files changed, 7 insertions(+), 3 deletions(-) diff --git a/kernel/exit.c b/kernel/exit.c index 8a87021211ae..8e5e523dcc79 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -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; } diff --git a/kernel/fork.c b/kernel/fork.c index e832da9d15a4..9ce2d12ec701 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -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; diff --git a/kernel/pid.c b/kernel/pid.c index 3b96571d0fe6..76c2744493e2 100644 --- a/kernel/pid.c +++ b/kernel/pid.c @@ -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)) -- 2.53.0