[PATCH] simplify/fix first_tid()
first_tid: /* If nr exceeds the number of threads there is nothing todo */ if (nr) { if (nr >= get_nr_threads(leader)) goto done; } This is not reliable: sub-threads can exit after this check, so the 'for' loop below can overlap and proc_task_readdir() can return an already filldir'ed dirents. for (; pos && pid_alive(pos); pos = next_thread(pos)) { if (--nr > 0) continue; Off-by-one error, will return 'leader' when nr == 1. This patch tries to fix these problems and simplify the code. Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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@ -2227,38 +2227,34 @@ int proc_pid_readdir(struct file * filp, void * dirent, filldir_t filldir)
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static struct task_struct *first_tid(struct task_struct *leader,
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int tid, int nr)
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{
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struct task_struct *pos = NULL;
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struct task_struct *pos;
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rcu_read_lock();
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/* Attempt to start with the pid of a thread */
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if (tid && (nr > 0)) {
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pos = find_task_by_pid(tid);
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if (pos && (pos->group_leader != leader))
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pos = NULL;
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if (pos)
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nr = 0;
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if (pos && (pos->group_leader == leader))
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goto found;
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}
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/* If nr exceeds the number of threads there is nothing todo */
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if (nr) {
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if (nr >= get_nr_threads(leader))
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goto done;
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}
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/* If we haven't found our starting place yet start with the
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* leader and walk nr threads forward.
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*/
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if (!pos && (nr >= 0))
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pos = leader;
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for (; pos && pid_alive(pos); pos = next_thread(pos)) {
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if (--nr > 0)
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continue;
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get_task_struct(pos);
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goto done;
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}
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pos = NULL;
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done:
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if (nr && nr >= get_nr_threads(leader))
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goto out;
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/* If we haven't found our starting place yet start
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* with the leader and walk nr threads forward.
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*/
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for (pos = leader; nr > 0; --nr) {
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pos = next_thread(pos);
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if (pos == leader) {
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pos = NULL;
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goto out;
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}
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}
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found:
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get_task_struct(pos);
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out:
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rcu_read_unlock();
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return pos;
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}
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