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-rw-r--r--debian/patches-rt/0134-printk-Avoid-false-positive-lockdep-report-for-legac.patch64
1 files changed, 64 insertions, 0 deletions
diff --git a/debian/patches-rt/0134-printk-Avoid-false-positive-lockdep-report-for-legac.patch b/debian/patches-rt/0134-printk-Avoid-false-positive-lockdep-report-for-legac.patch
new file mode 100644
index 0000000000..225e8db694
--- /dev/null
+++ b/debian/patches-rt/0134-printk-Avoid-false-positive-lockdep-report-for-legac.patch
@@ -0,0 +1,64 @@
+From: John Ogness <john.ogness@linutronix.de>
+Date: Mon, 11 Dec 2023 09:34:16 +0000
+Subject: [PATCH 134/134] printk: Avoid false positive lockdep report for
+ legacy driver.
+Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.6/older/patches-6.6.7-rt18.tar.xz
+
+printk may invoke the legacy console driver from atomic context. This leads to
+a lockdep splat because the console driver will acquire a sleeping lock and the
+caller may also hold a spinning lock. This is noticed by lockdep on !PREEMPT_RT
+configurations because it will also lead to a problem on PREEMPT_RT.
+
+On PREEMPT_RT the atomic path is always avoided and the console driver is
+always invoked from a dedicated thread. Thus the lockdep splat is a false
+positive.
+
+Override the lock-context before invoking the console driver.
+
+Signed-off-by: John Ogness <john.ogness@linutronix.de>
+Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
+---
+ kernel/printk/printk.c | 9 ++++++++-
+ 1 file changed, 8 insertions(+), 1 deletion(-)
+
+--- a/kernel/printk/printk.c
++++ b/kernel/printk/printk.c
+@@ -2817,6 +2817,8 @@ static void __console_unlock(void)
+ up_console_sem();
+ }
+
++static DEFINE_WAIT_OVERRIDE_MAP(printk_legacy_map, LD_WAIT_SLEEP);
++
+ #ifdef CONFIG_PRINTK
+
+ /*
+@@ -2985,7 +2987,7 @@ static bool console_emit_next_record(str
+ /*
+ * On PREEMPT_RT this function is either in a thread or
+ * panic context. So there is no need for concern about
+- * printk reentrance or handovers.
++ * printk reentrance, handovers, or lockdep complaints.
+ */
+
+ con->write(con, outbuf, pmsg.outbuf_len);
+@@ -3007,7 +3009,9 @@ static bool console_emit_next_record(str
+ /* Do not trace print latency. */
+ stop_critical_timings();
+
++ lock_map_acquire_try(&printk_legacy_map);
+ con->write(con, outbuf, pmsg.outbuf_len);
++ lock_map_release(&printk_legacy_map);
+
+ start_critical_timings();
+
+@@ -3084,7 +3088,10 @@ static bool console_flush_all(bool do_co
+ any_usable = true;
+
+ if (flags & CON_NBCON) {
++
++ lock_map_acquire_try(&printk_legacy_map);
+ progress = nbcon_atomic_emit_next_record(con, handover, cookie);
++ lock_map_release(&printk_legacy_map);
+
+ printk_seq = nbcon_seq_read(con);
+ } else {