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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>
This commit is contained in:
Oleg Nesterov 2014-12-10 15:45:21 -08:00 committed by Linus Torvalds
parent abdba6e9ea
commit a90e984c8a
1 changed files with 3 additions and 1 deletions
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4
kernel/sched/core.c
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@ -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,