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pid: document the PIDNS_ADDING checks in alloc_pid() and copy_process()

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Both copy_process() and alloc_pid() do the same PIDNS_ADDING check.  The
reasons for these checks, and the fact that both are necessary, are not
immediately obvious.  Add the comments.

Link: https://lkml.kernel.org/r/aaGIRElc78U4Er42@redhat.com
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Adrian Reber <areber@redhat.com>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Cc: Alexander Mikhalitsyn <alexander@mihalicyn.com>
Cc: Andrei Vagin <avagin@gmail.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Kees Cook <kees@kernel.org>
Cc: Kirill Tkhai <tkhai@ya.ru>
Cc: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Oleg Nesterov
2026-02-27 13:04:20 +01:00
committed by Andrew Morton
parent 040261b118
commit 8fba1920ac
2 changed files with 10 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files

6
kernel/fork.c
View File

@@ -2393,7 +2393,11 @@ __latent_entropy struct task_struct *copy_process(
rseq_fork(p, clone_flags);
/* Don't start children in a dying pid namespace */
/*
* If zap_pid_ns_processes() was called after alloc_pid(), the new
* child missed SIGKILL. If current is not in the same namespace,
* we can't rely on fatal_signal_pending() below.
*/
if (unlikely(!(ns_of_pid(pid)->pid_allocated & PIDNS_ADDING))) {
retval = -ENOMEM;
goto bad_fork_core_free;

5
kernel/pid.c
View File

@@ -314,6 +314,11 @@ struct pid *alloc_pid(struct pid_namespace *ns, pid_t *arg_set_tid,
*
* This can't be done earlier because we need to preserve other
* error conditions.
*
* We need this even if copy_process() does the same check. If two
* or more tasks from parent namespace try to inject a child into a
* dead namespace, one of free_pid() calls from the copy_process()
* error path may try to wakeup the possibly freed ns->child_reaper.
*/
retval = -ENOMEM;
if (unlikely(!(ns->pid_allocated & PIDNS_ADDING)))