The patch titled
pids: init_struct_pid.tasks should never see the swapper process
has been added to the -mm tree. Its filename is
pids-init_struct_pidtasks-should-never-see-the-swapper-process.patch
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------------------------------------------------------
Subject: pids: init_struct_pid.tasks should never see the swapper process
From: Oleg Nesterov <oleg@xxxxxxxxxx>
"statically initialize struct pid for swapper" commit 820e45db says:
Statically initialize a struct pid for the swapper process (pid_t == 0)
and attach it to init_task. This is needed so task_pid(), task_pgrp()
and task_session() interfaces work on the swapper process also.
OK, but:
- it doesn't make sense to add init_task.pids[].node into
init_struct_pid.tasks[], and in fact this just wrong.
idle threads are special, they shouldn't be visible on any
global list. In particular do_each_pid_task(init_struct_pid)
shouldn't see swapper.
This is the actual reason why kill(0, SIGKILL) from /sbin/init
(which starts with 0,0 special pids) crashes the kernel. The
signal sent to pgid/sid == 0 must never see idle threads, even
if the previous patch fixed the crash itself.
- we have other idle threads running on the non-boot CPUs, see
the next patch.
Change INIT_STRUCT_PID/INIT_PID_LINK to create the empty/unhashed
hlist_head/hlist_node. Like any other idle thread swapper can never exit,
so detach_pid()->__hlist_del() is not possible, but we could change
INIT_PID_LINK() to set pprev = &next if needed.
All we need is the valid swapper->pids[].pid == &init_struct_pid.
Reported-by: Mathias Krause <mathias.krause@xxxxxxxxxxx>
Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Cedric Le Goater <clg@xxxxxxxxxx>
Cc: Dave Hansen <haveblue@xxxxxxxxxx>
Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Herbert Poetzl <herbert@xxxxxxxxxxxx>
Cc: Mathias Krause <Mathias.Krause@xxxxxxxxxxx>
Cc: Roland McGrath <roland@xxxxxxxxxx>
Cc: Serge Hallyn <serue@xxxxxxxxxx>
Cc: Sukadev Bhattiprolu <sukadev@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/init_task.h | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff -puN include/linux/init_task.h~pids-init_struct_pidtasks-should-never-see-the-swapper-process include/linux/init_task.h
--- a/include/linux/init_task.h~pids-init_struct_pidtasks-should-never-see-the-swapper-process
+++ a/include/linux/init_task.h
@@ -45,9 +45,9 @@ extern struct group_info init_groups;
#define INIT_STRUCT_PID { \
.count = ATOMIC_INIT(1), \
.tasks = { \
- { .first = &init_task.pids[PIDTYPE_PID].node }, \
- { .first = &init_task.pids[PIDTYPE_PGID].node }, \
- { .first = &init_task.pids[PIDTYPE_SID].node }, \
+ { .first = NULL }, \
+ { .first = NULL }, \
+ { .first = NULL }, \
}, \
.level = 0, \
.numbers = { { \
@@ -61,7 +61,7 @@ extern struct group_info init_groups;
{ \
.node = { \
.next = NULL, \
- .pprev = &init_struct_pid.tasks[type].first, \
+ .pprev = NULL, \
}, \
.pid = &init_struct_pid, \
}
_
Patches currently in -mm which might be from oleg@xxxxxxxxxx are
linux-next.patch
cpu-timers-optimize-run_posix_cpu_timers.patch
oom-select_bad_process-check-pf_kthread-instead-of-mm-to-skip-kthreads.patch
oom-select_bad_process-pf_exiting-check-should-take-mm-into-account.patch
oom-introduce-find_lock_task_mm-to-fix-mm-false-positives.patch
oom-oom_forkbomb_penalty-move-thread_group_cputime-out-of-task_lock.patch
oom-hold-tasklist_lock-when-dumping-tasks.patch
oom-give-current-access-to-memory-reserves-if-it-has-been-killed.patch
oom-avoid-sending-exiting-tasks-a-sigkill.patch
oom-clean-up-oom_kill_task.patch
oom-clean-up-oom_badness.patch
oom-select_bad_process-never-choose-tasks-with-badness-==-0.patch
kmod-add-init-function-to-usermodehelper.patch
exec-replace-call_usermodehelper_pipe-with-use-of-umh-init-function-and-resolve-limit.patch
umh-creds-convert-call_usermodehelper_keys-to-use-subprocess_info-init.patch
umh-creds-kill-subprocess_info-cred-logic.patch
call_usermodehelper-no-need-to-unblock-signals.patch
wait_for_helper-sigchld-from-user-space-can-lead-to-use-after-free.patch
call_usermodehelper-simplify-fix-umh_no_wait-case.patch
call_usermodehelper-umh_wait_exec-ignores-kernel_thread-failure.patch
coredump-factor-out-the-not-ispipe-file-checks.patch
coredump-cleanup-ispipe-code.patch
coredump-factor-out-put_cred-calls.patch
coredump-shift-down_writemmap_sem-into-coredump_wait.patch
exit-exit_notify-can-trust-signal-notify_count-0.patch
exit-change-zap_other_threads-to-count-sub-threads.patch
exit-avoid-sig-count-in-de_thread-__exit_signal-synchronization.patch
exit-avoid-sig-count-in-__exit_signal-to-detect-the-group-dead-case.patch
posix-cpu-timers-avoid-task-signal-=-null-checks.patch
ia64-ptrace_attach_sync_user_rbs-avoid-task-signal-=-null-checks.patch
fork-exit-move-tty_kref_put-outside-of-__cleanup_signal.patch
signals-make-task_struct-signal-immutable-refcountable.patch
signals-clear-signal-tty-when-the-last-thread-exits.patch
signals-clear-signal-tty-when-the-last-thread-exits-fix.patch
signals-kill-the-awful-task_rq_unlock_wait-hack.patch
exit-__exit_signal-use-thread_group_leader-consistently.patch
kill-the-obsolete-thread_group_cputime_free-and-taskstats_tgid_init-helpers.patch
exit-move-taskstats_tgid_free-from-__exit_signal-to-free_signal_struct.patch
check_unshare_flags-kill-the-bogus-clone_sighand-sig-count-check.patch
proc-get_nr_threads-doesnt-need-siglock-any-longer.patch
proc_sched_show_task-use-get_nr_threads.patch
keyctl_session_to_parent-use-thread_group_empty-to-check-singlethreadness.patch
proc-turn-signal_struct-count-into-int-nr_threads.patch
proc-turn-signal_struct-count-into-int-nr_threads-checkpatch-fixes.patch
proc-cleanup-remove-unused-assignments.patch
init_task-should-initialize-thread_group-list.patch
pids-init_struct_pidtasks-should-never-see-the-swapper-process.patch
pids-fix-fork_idle-to-setup-pids-correctly.patch
init_sighand-use-sig_dfl-instead-of-null.patch
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