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posix-cpu-timers: fix race between handle_posix_cpu_timers() and posix_cpu_timer_del()
commitf90fff1e15
upstream. If an exiting non-autoreaping task has already passed exit_notify() and calls handle_posix_cpu_timers() from IRQ, it can be reaped by its parent or debugger right after unlock_task_sighand(). If a concurrent posix_cpu_timer_del() runs at that moment, it won't be able to detect timer->it.cpu.firing != 0: cpu_timer_task_rcu() and/or lock_task_sighand() will fail. Add the tsk->exit_state check into run_posix_cpu_timers() to fix this. This fix is not needed if CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y, because exit_task_work() is called before exit_notify(). But the check still makes sense, task_work_add(&tsk->posix_cputimers_work.work) will fail anyway in this case. Cc: stable@vger.kernel.org Reported-by: Benoît Sevens <bsevens@google.com> Fixes:0bdd2ed413
("sched: run_posix_cpu_timers: Don't check ->exit_state, use lock_task_sighand()") Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -1400,6 +1400,15 @@ void run_posix_cpu_timers(void)
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lockdep_assert_irqs_disabled();
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/*
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* Ensure that release_task(tsk) can't happen while
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* handle_posix_cpu_timers() is running. Otherwise, a concurrent
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* posix_cpu_timer_del() may fail to lock_task_sighand(tsk) and
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* miss timer->it.cpu.firing != 0.
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*/
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if (tsk->exit_state)
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return;
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/*
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* If the actual expiry is deferred to task work context and the
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* work is already scheduled there is no point to do anything here.
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