From a90e984c8a660dd58894a68cc5d9d5cd457d5796 Mon Sep 17 00:00:00 2001 From: Oleg Nesterov <oleg@redhat.com> Date: Wed, 10 Dec 2014 15:45:21 -0800 Subject: [PATCH] sched_show_task: fix unsafe usage of ->real_parent rcu_read_lock() can not protect p->real_parent if release_task(p) was already called, change sched_show_task() to check pis_alive() like other users do. Note: we need some helpers to cleanup the code like this. And it seems that that the usage of cpu_curr(cpu) in dump_cpu_task() is not safe too. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Cc: Aaron Tomlin <atomlin@redhat.com> Cc: Alexey Dobriyan <adobriyan@gmail.com> Cc: "Eric W. Biederman" <ebiederm@xmission.com>, Cc: Sterling Alexander <stalexan@redhat.com> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Roland McGrath <roland@hack.frob.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> --- kernel/sched/core.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index bb398c0c5f085..b5797b78add65 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4527,8 +4527,10 @@ void sched_show_task(struct task_struct *p) #ifdef CONFIG_DEBUG_STACK_USAGE free = stack_not_used(p); #endif + ppid = 0; rcu_read_lock(); - ppid = task_pid_nr(rcu_dereference(p->real_parent)); + if (pid_alive(p)) + ppid = task_pid_nr(rcu_dereference(p->real_parent)); rcu_read_unlock(); printk(KERN_CONT "%5lu %5d %6d 0x%08lx\n", free, task_pid_nr(p), ppid, -- GitLab