54 lines
2.0 KiB
Diff
54 lines
2.0 KiB
Diff
From b9cc1762c1cb78dc3ea579526c2810aaa5095b76 Mon Sep 17 00:00:00 2001
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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Date: Thu, 3 Aug 2023 12:09:32 +0200
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Subject: [PATCH 009/196] signal: Don't disable preemption in ptrace_stop() on
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PREEMPT_RT.
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On PREEMPT_RT keeping preemption disabled during the invocation of
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cgroup_enter_frozen() is a problem because the function acquires css_set_lock
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which is a sleeping lock on PREEMPT_RT and must not be acquired with disabled
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preemption.
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The preempt-disabled section is only for performance optimisation
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reasons and can be avoided.
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Extend the comment and don't disable preemption before scheduling on
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PREEMPT_RT.
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Acked-by: Oleg Nesterov <oleg@redhat.com>
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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Link: https://lore.kernel.org/r/20230803100932.325870-3-bigeasy@linutronix.de
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---
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kernel/signal.c | 13 +++++++++++--
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1 file changed, 11 insertions(+), 2 deletions(-)
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diff --git a/kernel/signal.c b/kernel/signal.c
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index 051ed8114cd4..b71026341056 100644
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--- a/kernel/signal.c
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+++ b/kernel/signal.c
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@@ -2344,11 +2344,20 @@ static int ptrace_stop(int exit_code, int why, unsigned long message,
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* The preempt-disable section ensures that there will be no preemption
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* between unlock and schedule() and so improving the performance since
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* the ptracer has no reason to sleep.
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+ *
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+ * On PREEMPT_RT locking tasklist_lock does not disable preemption.
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+ * Therefore the task can be preempted (after
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+ * do_notify_parent_cldstop()) before unlocking tasklist_lock so there
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+ * is no benefit in doing this. The optimisation is harmful on
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+ * PEEMPT_RT because the spinlock_t (in cgroup_enter_frozen()) must not
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+ * be acquired with disabled preemption.
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*/
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- preempt_disable();
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+ if (!IS_ENABLED(CONFIG_PREEMPT_RT))
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+ preempt_disable();
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read_unlock(&tasklist_lock);
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cgroup_enter_frozen();
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- preempt_enable_no_resched();
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+ if (!IS_ENABLED(CONFIG_PREEMPT_RT))
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+ preempt_enable_no_resched();
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schedule();
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cgroup_leave_frozen(true);
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--
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2.43.2
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