64 lines
2.2 KiB
Diff
64 lines
2.2 KiB
Diff
From: John Ogness <john.ogness@linutronix.de>
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Date: Mon, 11 Dec 2023 09:34:16 +0000
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Subject: [PATCH 134/134] printk: Avoid false positive lockdep report for
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legacy driver.
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Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz
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printk may invoke the legacy console driver from atomic context. This leads to
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a lockdep splat because the console driver will acquire a sleeping lock and the
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caller may also hold a spinning lock. This is noticed by lockdep on !PREEMPT_RT
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configurations because it will also lead to a problem on PREEMPT_RT.
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On PREEMPT_RT the atomic path is always avoided and the console driver is
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always invoked from a dedicated thread. Thus the lockdep splat is a false
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positive.
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Override the lock-context before invoking the console driver.
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Signed-off-by: John Ogness <john.ogness@linutronix.de>
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Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
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---
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kernel/printk/printk.c | 9 ++++++++-
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1 file changed, 8 insertions(+), 1 deletion(-)
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--- a/kernel/printk/printk.c
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+++ b/kernel/printk/printk.c
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@@ -2817,6 +2817,8 @@ static void __console_unlock(void)
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up_console_sem();
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}
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+static DEFINE_WAIT_OVERRIDE_MAP(printk_legacy_map, LD_WAIT_SLEEP);
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+
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#ifdef CONFIG_PRINTK
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/*
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@@ -2985,7 +2987,7 @@ static bool console_emit_next_record(str
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/*
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* On PREEMPT_RT this function is either in a thread or
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* panic context. So there is no need for concern about
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- * printk reentrance or handovers.
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+ * printk reentrance, handovers, or lockdep complaints.
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*/
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con->write(con, outbuf, pmsg.outbuf_len);
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@@ -3007,7 +3009,9 @@ static bool console_emit_next_record(str
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/* Do not trace print latency. */
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stop_critical_timings();
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+ lock_map_acquire_try(&printk_legacy_map);
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con->write(con, outbuf, pmsg.outbuf_len);
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+ lock_map_release(&printk_legacy_map);
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start_critical_timings();
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@@ -3084,7 +3088,10 @@ static bool console_flush_all(bool do_co
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any_usable = true;
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if (flags & CON_NBCON) {
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+
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+ lock_map_acquire_try(&printk_legacy_map);
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progress = nbcon_atomic_emit_next_record(con, handover, cookie);
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+ lock_map_release(&printk_legacy_map);
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printk_seq = nbcon_seq_read(con);
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} else {
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