Merge tag 'printk-for-6.2' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux

Pull printk updates from Petr Mladek:

 - Add NMI-safe SRCU reader API. It uses atomic_inc() instead of
   this_cpu_inc() on strong load-store architectures.

 - Introduce new console_list_lock to synchronize a manipulation of the
   list of registered consoles and their flags.

   This is a first step in removing the big-kernel-lock-like behavior of
   console_lock(). This semaphore still serializes console->write()
   calbacks against:

      - each other. It primary prevents potential races between early
        and proper console drivers using the same device.

      - suspend()/resume() callbacks and init() operations in some
        drivers.

      - various other operations in the tty/vt and framebufer
        susbsystems. It is likely that console_lock() serializes even
        operations that are not directly conflicting with the
        console->write() callbacks here. This is the most complicated
        big-kernel-lock aspect of the console_lock() that will be hard
        to untangle.

 - Introduce new console_srcu lock that is used to safely iterate and
   access the registered console drivers under SRCU read lock.

   This is a prerequisite for introducing atomic console drivers and
   console kthreads. It will reduce the complexity of serialization
   against normal consoles and console_lock(). Also it should remove the
   risk of deadlock during critical situations, like Oops or panic, when
   only atomic consoles are registered.

 - Check whether the console is registered instead of enabled on many
   locations. It was a historical leftover.

 - Cleanly force a preferred console in xenfb code instead of a dirty
   hack.

 - A lot of code and comment clean ups and improvements.

* tag 'printk-for-6.2' of git://git.kernel.org/pub/scm/linux/kernel/git/printk/linux: (47 commits)
  printk: htmldocs: add missing description
  tty: serial: sh-sci: use setup() callback for early console
  printk: relieve console_lock of list synchronization duties
  tty: serial: kgdboc: use console_list_lock to trap exit
  tty: serial: kgdboc: synchronize tty_find_polling_driver() and register_console()
  tty: serial: kgdboc: use console_list_lock for list traversal
  tty: serial: kgdboc: use srcu console list iterator
  proc: consoles: use console_list_lock for list iteration
  tty: tty_io: use console_list_lock for list synchronization
  printk, xen: fbfront: create/use safe function for forcing preferred
  netconsole: avoid CON_ENABLED misuse to track registration
  usb: early: xhci-dbc: use console_is_registered()
  tty: serial: xilinx_uartps: use console_is_registered()
  tty: serial: samsung_tty: use console_is_registered()
  tty: serial: pic32_uart: use console_is_registered()
  tty: serial: earlycon: use console_is_registered()
  tty: hvc: use console_is_registered()
  efi: earlycon: use console_is_registered()
  tty: nfcon: use console_is_registered()
  serial_core: replace uart_console_enabled() with uart_console_registered()
  ...

5 files changed, 26 insertions, 24 deletions

diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
index 05106e6fbd0e..ab62074174c3 100644
--- a/kernel/rcu/Kconfig
+++ b/kernel/rcu/Kconfig
@@ -54,21 +54,17 @@ config RCU_EXPERT
 	  Say N if you are unsure.
 
 config SRCU
-	bool
-	help
-	  This option selects the sleepable version of RCU. This version
-	  permits arbitrary sleeping or blocking within RCU read-side critical
-	  sections.
+	def_bool y
 
 config TINY_SRCU
 	bool
-	default y if SRCU && TINY_RCU
+	default y if TINY_RCU
 	help
 	  This option selects the single-CPU non-preemptible version of SRCU.
 
 config TREE_SRCU
 	bool
-	default y if SRCU && !TINY_RCU
+	default y if !TINY_RCU
 	help
 	  This option selects the full-fledged version of SRCU.
 
@@ -77,7 +73,6 @@ config NEED_SRCU_NMI_SAFE
 
 config TASKS_RCU_GENERIC
 	def_bool TASKS_RCU || TASKS_RUDE_RCU || TASKS_TRACE_RCU
-	select SRCU
 	help
 	  This option enables generic infrastructure code supporting
 	  task-based RCU implementations.  Not for manual selection.
diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug
index 1b0c41d490f0..232e29fe3e5e 100644
--- a/kernel/rcu/Kconfig.debug
+++ b/kernel/rcu/Kconfig.debug
@@ -27,7 +27,6 @@ config RCU_SCALE_TEST
 	tristate "performance tests for RCU"
 	depends on DEBUG_KERNEL
 	select TORTURE_TEST
-	select SRCU
 	default n
 	help
 	  This option provides a kernel module that runs performance
@@ -43,7 +42,6 @@ config RCU_TORTURE_TEST
 	tristate "torture tests for RCU"
 	depends on DEBUG_KERNEL
 	select TORTURE_TEST
-	select SRCU
 	default n
 	help
 	  This option provides a kernel module that runs torture tests
@@ -59,7 +57,6 @@ config RCU_REF_SCALE_TEST
 	tristate "Scalability tests for read-side synchronization (RCU and others)"
 	depends on DEBUG_KERNEL
 	select TORTURE_TEST
-	select SRCU
 	default n
 	help
 	  This option provides a kernel module that runs performance tests
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 65704cbc9df7..c5aa934de59b 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -286,7 +286,7 @@ void rcu_test_sync_prims(void);
  */
 extern void resched_cpu(int cpu);
 
-#if defined(CONFIG_SRCU) || !defined(CONFIG_TINY_RCU)
+#if !defined(CONFIG_TINY_RCU)
 
 #include <linux/rcu_node_tree.h>
 
@@ -375,6 +375,10 @@ extern void rcu_init_geometry(void);
 	     (cpu) <= rnp->grphi; \
 	     (cpu) = rcu_find_next_bit((rnp), (cpu) + 1 - (rnp->grplo), (mask)))
 
+#endif /* !defined(CONFIG_TINY_RCU) */
+
+#if !defined(CONFIG_TINY_RCU) || defined(CONFIG_TASKS_RCU_GENERIC)
+
 /*
  * Wrappers for the rcu_node::lock acquire and release.
  *
@@ -437,7 +441,7 @@ do {									\
 #define raw_lockdep_assert_held_rcu_node(p)				\
 	lockdep_assert_held(&ACCESS_PRIVATE(p, lock))
 
-#endif /* #if defined(CONFIG_SRCU) || !defined(CONFIG_TINY_RCU) */
+#endif // #if !defined(CONFIG_TINY_RCU) || defined(CONFIG_TASKS_RCU_GENERIC)
 
 #ifdef CONFIG_TINY_RCU
 /* Tiny RCU doesn't expedite, as its purpose in life is instead to be tiny. */
diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c
index 33adafdad261..b12fb0cec44d 100644
--- a/kernel/rcu/srcutiny.c
+++ b/kernel/rcu/srcutiny.c
@@ -197,6 +197,16 @@ void synchronize_srcu(struct srcu_struct *ssp)
 {
 	struct rcu_synchronize rs;
 
+	RCU_LOCKDEP_WARN(lockdep_is_held(ssp) ||
+			lock_is_held(&rcu_bh_lock_map) ||
+			lock_is_held(&rcu_lock_map) ||
+			lock_is_held(&rcu_sched_lock_map),
+			"Illegal synchronize_srcu() in same-type SRCU (or in RCU) read-side critical section");
+
+	if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
+		return;
+
+	might_sleep();
 	init_rcu_head_on_stack(&rs.head);
 	init_completion(&rs.completion);
 	call_srcu(ssp, &rs.head, wakeme_after_rcu);
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 738842c4886b..f5e6a2f95a2a 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -224,7 +224,7 @@ void rcu_test_sync_prims(void)
 	synchronize_rcu_expedited();
 }
 
-#if !defined(CONFIG_TINY_RCU) || defined(CONFIG_SRCU)
+#if !defined(CONFIG_TINY_RCU)
 
 /*
  * Switch to run-time mode once RCU has fully initialized.
@@ -239,7 +239,7 @@ static int __init rcu_set_runtime_mode(void)
 }
 core_initcall(rcu_set_runtime_mode);
 
-#endif /* #if !defined(CONFIG_TINY_RCU) || defined(CONFIG_SRCU) */
+#endif /* #if !defined(CONFIG_TINY_RCU) */
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 static struct lock_class_key rcu_lock_key;
@@ -559,10 +559,8 @@ static void early_boot_test_call_rcu(void)
 	struct early_boot_kfree_rcu *rhp;
 
 	call_rcu(&head, test_callback);
-	if (IS_ENABLED(CONFIG_SRCU)) {
-		early_srcu_cookie = start_poll_synchronize_srcu(&early_srcu);
-		call_srcu(&early_srcu, &shead, test_callback);
-	}
+	early_srcu_cookie = start_poll_synchronize_srcu(&early_srcu);
+	call_srcu(&early_srcu, &shead, test_callback);
 	rhp = kmalloc(sizeof(*rhp), GFP_KERNEL);
 	if (!WARN_ON_ONCE(!rhp))
 		kfree_rcu(rhp, rh);
@@ -585,11 +583,9 @@ static int rcu_verify_early_boot_tests(void)
 	if (rcu_self_test) {
 		early_boot_test_counter++;
 		rcu_barrier();
-		if (IS_ENABLED(CONFIG_SRCU)) {
-			early_boot_test_counter++;
-			srcu_barrier(&early_srcu);
-			WARN_ON_ONCE(!poll_state_synchronize_srcu(&early_srcu, early_srcu_cookie));
-		}
+		early_boot_test_counter++;
+		srcu_barrier(&early_srcu);
+		WARN_ON_ONCE(!poll_state_synchronize_srcu(&early_srcu, early_srcu_cookie));
 	}
 	if (rcu_self_test_counter != early_boot_test_counter) {
 		WARN_ON(1);