Messages in this thread Patch in this message | | | Date | Mon, 10 May 2010 21:50:14 +0200 | From | Oleg Nesterov <> | Subject | [PATCH 2/4] pids: init_struct_pid.tasks should never see the swapper process |
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"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@secunet.com> Signed-off-by: Oleg Nesterov <oleg@redhat.com> ---
include/linux/init_task.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
--- 34-rc1/include/linux/init_task.h~2_INIT_PID_DONT_LINK_SWAPPER 2010-05-10 19:45:27.000000000 +0200 +++ 34-rc1/include/linux/init_task.h 2010-05-10 20:26:08.000000000 +0200 @@ -53,9 +53,9 @@ 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 }, \ }, \ .rcu = RCU_HEAD_INIT, \ .level = 0, \ @@ -70,7 +70,7 @@ extern struct group_info init_groups; { \ .node = { \ .next = NULL, \ - .pprev = &init_struct_pid.tasks[type].first, \ + .pprev = NULL, \ }, \ .pid = &init_struct_pid, \ }
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