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rcu-tasks: Don't delete holdouts within trc_inspect_reader()
As Yanfei pointed out, although invoking trc_del_holdout() is safe from the viewpoint of the integrity of the holdout list itself, the put_task_struct() invoked by trc_del_holdout() can result in use-after-free errors due to later accesses to this task_struct structure by the RCU Tasks Trace grace-period kthread. This commit therefore removes this call to trc_del_holdout() from trc_inspect_reader() in favor of the grace-period thread's existing call to trc_del_holdout(), thus eliminating that particular class of use-after-free errors. Reported-by: "Xu, Yanfei" <yanfei.xu@windriver.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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@ -953,10 +953,9 @@ static bool trc_inspect_reader(struct task_struct *t, void *arg)
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in_qs = likely(!t->trc_reader_nesting);
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in_qs = likely(!t->trc_reader_nesting);
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}
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}
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// Mark as checked. Because this is called from the grace-period
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// Mark as checked so that the grace-period kthread will
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// kthread, also remove the task from the holdout list.
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// remove it from the holdout list.
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t->trc_reader_checked = true;
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t->trc_reader_checked = true;
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trc_del_holdout(t);
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if (in_qs)
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if (in_qs)
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return true; // Already in quiescent state, done!!!
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return true; // Already in quiescent state, done!!!
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