diff options
Diffstat (limited to 'debian/patches-rt/0002-signal-Don-t-disable-preemption-in-ptrace_stop-on-PR.patch')
| -rw-r--r-- | debian/patches-rt/0002-signal-Don-t-disable-preemption-in-ptrace_stop-on-PR.patch | 66 |
1 files changed, 66 insertions, 0 deletions
diff --git a/debian/patches-rt/0002-signal-Don-t-disable-preemption-in-ptrace_stop-on-PR.patch b/debian/patches-rt/0002-signal-Don-t-disable-preemption-in-ptrace_stop-on-PR.patch new file mode 100644 index 000000000..05ec116ad --- /dev/null +++ b/debian/patches-rt/0002-signal-Don-t-disable-preemption-in-ptrace_stop-on-PR.patch @@ -0,0 +1,66 @@ +From d5541b6ef4eccee650abfe3095b9e7365773494c Mon Sep 17 00:00:00 2001 +From: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +Date: Wed, 22 Jun 2022 11:36:17 +0200 +Subject: [PATCH 02/62] signal: Don't disable preemption in ptrace_stop() on + PREEMPT_RT. +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.1/older/patches-6.1.69-rt21.tar.xz + +Commit + 53da1d9456fe7 ("fix ptrace slowness") + +is just band aid around the problem. +The invocation of do_notify_parent_cldstop() wakes the parent and makes +it runnable. The scheduler then wants to replace this still running task +with the parent. With the read_lock() acquired this is not possible +because preemption is disabled and so this is deferred until read_unlock(). +This scheduling point is undesired and is avoided by disabling preemption +around the unlock operation enabled again before the schedule() invocation +without a preemption point. +This is only undesired because the parent sleeps a cycle in +wait_task_inactive() until the traced task leaves the run-queue in +schedule(). It is not a correctness issue, it is just band aid to avoid the +visbile delay which sums up over multiple invocations. +The task can still be preempted if an interrupt occurs between +preempt_enable_no_resched() and freezable_schedule() because on the IRQ-exit +path of the interrupt scheduling _will_ happen. This is ignored since it does +not happen very often. + +On PREEMPT_RT keeping preemption disabled during the invocation of +cgroup_enter_frozen() becomes a problem because the function acquires +css_set_lock which is a sleeping lock on PREEMPT_RT and must not be +acquired with disabled preemption. + +Don't disable preemption on PREEMPT_RT. Remove the TODO regarding adding +read_unlock_no_resched() as there is no need for it and will cause harm. + +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +Link: https://lkml.kernel.org/r/20220720154435.232749-2-bigeasy@linutronix.de +--- + kernel/signal.c | 8 ++++---- + 1 file changed, 4 insertions(+), 4 deletions(-) + +diff --git a/kernel/signal.c b/kernel/signal.c +index 5d45f5da2b36..58e919c7c936 100644 +--- a/kernel/signal.c ++++ b/kernel/signal.c +@@ -2302,13 +2302,13 @@ static int ptrace_stop(int exit_code, int why, unsigned long message, + /* + * Don't want to allow preemption here, because + * sys_ptrace() needs this task to be inactive. +- * +- * XXX: implement read_unlock_no_resched(). + */ +- preempt_disable(); ++ if (!IS_ENABLED(CONFIG_PREEMPT_RT)) ++ preempt_disable(); + read_unlock(&tasklist_lock); + cgroup_enter_frozen(); +- preempt_enable_no_resched(); ++ if (!IS_ENABLED(CONFIG_PREEMPT_RT)) ++ preempt_enable_no_resched(); + schedule(); + cgroup_leave_frozen(true); + +-- +2.43.0 + |