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https://github.com/torvalds/linux
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d2e3ee9b29
- Fix the comment, is_single_threaded(p) actually means that nobody shares ->mm with p. I think this helper should be renamed, and it should not have arguments. With or without this patch it must not be used unless p == current, otherwise we can't safely use p->signal or p->mm. - "if (atomic_read(&p->signal->count) != 1)" is not right when we have a zombie group leader, use signal->live instead. - Add PF_KTHREAD check to skip kernel threads which may borrow p->mm, otherwise we can return the wrong "false". - Use for_each_process() instead of do_each_thread(), all threads must use the same ->mm. - Use down_write(mm->mmap_sem) + rcu_read_lock() instead of tasklist_lock to iterate over the process list. If there is another CLONE_VM process it can't pass exit_mm() which takes the same mm->mmap_sem. We can miss a freshly forked CLONE_VM task, but this doesn't matter because we must see its parent and return false. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Cc: David Howells <dhowells@redhat.com> Cc: James Morris <jmorris@namei.org> Cc: Roland McGrath <roland@redhat.com> Cc: Stephen Smalley <sds@tycho.nsa.gov> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: James Morris <jmorris@namei.org>
56 lines
1.2 KiB
C
56 lines
1.2 KiB
C
/* Function to determine if a thread group is single threaded or not
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*
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* Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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* - Derived from security/selinux/hooks.c
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public Licence
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* as published by the Free Software Foundation; either version
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* 2 of the Licence, or (at your option) any later version.
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*/
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#include <linux/sched.h>
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/*
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* Returns true if the task does not share ->mm with another thread/process.
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*/
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bool is_single_threaded(struct task_struct *task)
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{
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struct mm_struct *mm = task->mm;
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struct task_struct *p, *t;
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bool ret;
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might_sleep();
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if (atomic_read(&task->signal->live) != 1)
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return false;
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if (atomic_read(&mm->mm_users) == 1)
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return true;
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ret = false;
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down_write(&mm->mmap_sem);
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rcu_read_lock();
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for_each_process(p) {
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if (unlikely(p->flags & PF_KTHREAD))
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continue;
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if (unlikely(p == task->group_leader))
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continue;
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t = p;
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do {
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if (unlikely(t->mm == mm))
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goto found;
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if (likely(t->mm))
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break;
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} while_each_thread(p, t);
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}
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ret = true;
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found:
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rcu_read_unlock();
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up_write(&mm->mmap_sem);
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return ret;
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}
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