52 lines
1.9 KiB
Diff
52 lines
1.9 KiB
Diff
From b504e1cd491c55390370059280d5fbaa045d5543 Mon Sep 17 00:00:00 2001
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From: Oleg Nesterov <oleg@redhat.com>
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Date: Fri, 13 Jun 2025 19:26:50 +0200
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Subject: posix-cpu-timers: fix race between handle_posix_cpu_timers() and
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posix_cpu_timer_del()
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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If an exiting non-autoreaping task has already passed exit_notify() and
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calls handle_posix_cpu_timers() from IRQ, it can be reaped by its parent
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or debugger right after unlock_task_sighand().
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If a concurrent posix_cpu_timer_del() runs at that moment, it won't be
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able to detect timer->it.cpu.firing != 0: cpu_timer_task_rcu() and/or
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lock_task_sighand() will fail.
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Add the tsk->exit_state check into run_posix_cpu_timers() to fix this.
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This fix is not needed if CONFIG_POSIX_CPU_TIMERS_TASK_WORK=y, because
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exit_task_work() is called before exit_notify(). But the check still
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makes sense, task_work_add(&tsk->posix_cputimers_work.work) will fail
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anyway in this case.
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Cc: stable@vger.kernel.org
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Reported-by: Benoît Sevens <bsevens@google.com>
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Fixes: 0bdd2ed4138e ("sched: run_posix_cpu_timers: Don't check ->exit_state, use lock_task_sighand()")
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Signed-off-by: Oleg Nesterov <oleg@redhat.com>
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Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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---
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kernel/time/posix-cpu-timers.c | 9 +++++++++
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1 file changed, 9 insertions(+)
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--- a/kernel/time/posix-cpu-timers.c
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+++ b/kernel/time/posix-cpu-timers.c
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@@ -1406,6 +1406,15 @@ 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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+ /*
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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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*/
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