diff options
Diffstat (limited to 'debian/patches-rt/0048-printk-Avoid-false-positive-lockdep-report-for-legac.patch')
| -rw-r--r-- | debian/patches-rt/0048-printk-Avoid-false-positive-lockdep-report-for-legac.patch | 86 |
1 files changed, 86 insertions, 0 deletions
diff --git a/debian/patches-rt/0048-printk-Avoid-false-positive-lockdep-report-for-legac.patch b/debian/patches-rt/0048-printk-Avoid-false-positive-lockdep-report-for-legac.patch new file mode 100644 index 000000000..510b3c080 --- /dev/null +++ b/debian/patches-rt/0048-printk-Avoid-false-positive-lockdep-report-for-legac.patch @@ -0,0 +1,86 @@ +From: John Ogness <john.ogness@linutronix.de> +Date: Mon, 11 Dec 2023 09:34:16 +0000 +Subject: [PATCH 48/48] printk: Avoid false positive lockdep report for legacy + printing +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.8/older/patches-6.8.2-rt11.tar.xz + +Legacy console printing from printk() caller context may invoke +the console driver from atomic context. This leads to a lockdep +splat because the console driver will acquire a sleeping lock +and the caller may already hold a spinning lock. This is noticed +by lockdep on !PREEMPT_RT configurations because it will lead to +a problem on PREEMPT_RT. + +However, on PREEMPT_RT the printing path from atomic context is +always avoided and the console driver is always invoked from a +dedicated thread. Thus the lockdep splat on !PREEMPT_RT is a +false positive. + +For !PREEMPT_RT override the lock-context before invoking the +console driver to avoid the false positive. + +Do not override the lock-context for PREEMPT_RT in order to +allow lockdep to catch any real locking context issues related +to the write callback usage. + +Signed-off-by: John Ogness <john.ogness@linutronix.de> +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +--- + kernel/printk/printk.c | 31 ++++++++++++++++++++++++++++++- + 1 file changed, 30 insertions(+), 1 deletion(-) + +--- a/kernel/printk/printk.c ++++ b/kernel/printk/printk.c +@@ -2985,6 +2985,33 @@ bool printk_get_next_message(struct prin + } + + /* ++ * Legacy console printing from printk() caller context does not respect ++ * raw_spinlock/spinlock nesting. For !PREEMPT_RT the lockdep warning is a ++ * false positive. For PREEMPT_RT the false positive condition does not ++ * occur. ++ * ++ * This map is used to establish LD_WAIT_SLEEP context for the console write ++ * callbacks when legacy printing to avoid false positive lockdep complaints, ++ * thus allowing lockdep to continue to function for real issues. ++ */ ++#ifdef CONFIG_PREEMPT_RT ++static inline void printk_legacy_lock_map_acquire_try(void) { } ++static inline void printk_legacy_lock_map_release(void) { } ++#else ++static DEFINE_WAIT_OVERRIDE_MAP(printk_legacy_map, LD_WAIT_SLEEP); ++ ++static inline void printk_legacy_lock_map_acquire_try(void) ++{ ++ lock_map_acquire_try(&printk_legacy_map); ++} ++ ++static inline void printk_legacy_lock_map_release(void) ++{ ++ lock_map_release(&printk_legacy_map); ++} ++#endif /* CONFIG_PREEMPT_RT */ ++ ++/* + * Used as the printk buffers for non-panic, serialized console printing. + * This is for legacy (!CON_NBCON) as well as all boot (CON_BOOT) consoles. + * Its usage requires the console_lock held. +@@ -3039,7 +3066,7 @@ static bool console_emit_next_record(str + /* + * With forced threading 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); +@@ -3061,7 +3088,9 @@ static bool console_emit_next_record(str + /* Do not trace print latency. */ + stop_critical_timings(); + ++ printk_legacy_lock_map_acquire_try(); + con->write(con, outbuf, pmsg.outbuf_len); ++ printk_legacy_lock_map_release(); + + start_critical_timings(); + |