Revert "printk: add functions to prefer direct printing"

This reverts commit bc708ae997029e7c10de85b5512b2d0433ec3363.

The testing of 5.19 release candidates revealed missing synchronization
between early and regular console functionality.

It would be possible to start the console kthreads later as a workaround.
But it is clear that console lock serialized console drivers between
each other. It opens a big area of possible problems that were not
considered by people involved in the development and review.

printk() is crucial for debugging kernel issues and console output is
very important part of it. The number of consoles is huge and a proper
review would take some time. As a result it need to be reverted for 5.19.

Link: https://lore.kernel.org/r/YrBdjVwBOVgLfHyb@alley
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20220623145157.21938-7-pmladek@suse.com

diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 2884cd638d64b6466583cf7a6b14de011b540442..bbfd004449b5b81cb6ec1bad174415f5b12410a8 100644 (file)
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -578,7 +578,6 @@ void __handle_sysrq(int key, bool check_mask)
 
        rcu_sysrq_start();
        rcu_read_lock();
-       printk_prefer_direct_enter();
        /*
         * Raise the apparent loglevel to maximum so that the sysrq header
         * is shown to provide the user with positive feedback.  We do not
@@ -620,7 +619,6 @@ void __handle_sysrq(int key, bool check_mask)
                pr_cont("\n");
                console_loglevel = orig_log_level;
        }
-       printk_prefer_direct_exit();
        rcu_read_unlock();
        rcu_sysrq_end();
 

diff --git a/include/linux/printk.h b/include/linux/printk.h
index cd26aab0ab2a094d7fbb276cfa95f8486e9363b5..091fba7283e142af2c740e6b8cf36f080491dd9d 100644 (file)
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -170,9 +170,6 @@ extern void __printk_safe_exit(void);
 #define printk_deferred_enter __printk_safe_enter
 #define printk_deferred_exit __printk_safe_exit
 
-extern void printk_prefer_direct_enter(void);
-extern void printk_prefer_direct_exit(void);
-
 extern bool pr_flush(int timeout_ms, bool reset_on_progress);
 
 /*
@@ -225,14 +222,6 @@ static inline void printk_deferred_exit(void)
 {
 }
 
-static inline void printk_prefer_direct_enter(void)
-{
-}
-
-static inline void printk_prefer_direct_exit(void)
-{
-}
-
 static inline bool pr_flush(int timeout_ms, bool reset_on_progress)
 {
        return true;

diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index 02a65d55434092581ae852d19abdc58fb57f9fb3..52501e5f765547e0fa83824c5777ad7d45cce077 100644 (file)
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -127,8 +127,6 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
         * complain:
         */
        if (sysctl_hung_task_warnings) {
-               printk_prefer_direct_enter();
-
                if (sysctl_hung_task_warnings > 0)
                        sysctl_hung_task_warnings--;
                pr_err("INFO: task %s:%d blocked for more than %ld seconds.\n",
@@ -144,8 +142,6 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
 
                if (sysctl_hung_task_all_cpu_backtrace)
                        hung_task_show_all_bt = true;
-
-               printk_prefer_direct_exit();
        }
 
        touch_nmi_watchdog();
@@ -208,17 +204,12 @@ static void check_hung_uninterruptible_tasks(unsigned long timeout)
        }
  unlock:
        rcu_read_unlock();
-       if (hung_task_show_lock) {
-               printk_prefer_direct_enter();
+       if (hung_task_show_lock)
                debug_show_all_locks();
-               printk_prefer_direct_exit();
-       }
 
        if (hung_task_show_all_bt) {
                hung_task_show_all_bt = false;
-               printk_prefer_direct_enter();
                trigger_all_cpu_backtrace();
-               printk_prefer_direct_exit();
        }
 
        if (hung_task_call_panic)

diff --git a/kernel/panic.c b/kernel/panic.c
index 6737b23322753a2c89954a98ef4e6038fc09b3a1..8355b19676f845667b2fb2924e8d99eec5384c40 100644 (file)
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -579,8 +579,6 @@ void __warn(const char *file, int line, void *caller, unsigned taint,
 {
        disable_trace_on_warning();
 
-       printk_prefer_direct_enter();
-
        if (file)
                pr_warn("WARNING: CPU: %d PID: %d at %s:%d %pS\n",
                        raw_smp_processor_id(), current->pid, file, line,
@@ -610,8 +608,6 @@ void __warn(const char *file, int line, void *caller, unsigned taint,
 
        /* Just a warning, don't kill lockdep. */
        add_taint(taint, LOCKDEP_STILL_OK);
-
-       printk_prefer_direct_exit();
 }
 
 #ifndef __WARN_FLAGS

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 5a6273e56b4e9458b1581a3e3248e302fda9d81b..b49c6ff6dca01ba9f5acf0834654da65634b61e3 100644 (file)
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -362,34 +362,6 @@ static int console_msg_format = MSG_FORMAT_DEFAULT;
 static DEFINE_MUTEX(syslog_lock);
 
 #ifdef CONFIG_PRINTK
-static atomic_t printk_prefer_direct = ATOMIC_INIT(0);
-
-/**
- * printk_prefer_direct_enter - cause printk() calls to attempt direct
- *                              printing to all enabled consoles
- *
- * Since it is not possible to call into the console printing code from any
- * context, there is no guarantee that direct printing will occur.
- *
- * This globally effects all printk() callers.
- *
- * Context: Any context.
- */
-void printk_prefer_direct_enter(void)
-{
-       atomic_inc(&printk_prefer_direct);
-}
-
-/**
- * printk_prefer_direct_exit - restore printk() behavior
- *
- * Context: Any context.
- */
-void printk_prefer_direct_exit(void)
-{
-       WARN_ON(atomic_dec_if_positive(&printk_prefer_direct) < 0);
-}
-
 DECLARE_WAIT_QUEUE_HEAD(log_wait);
 /* All 3 protected by @syslog_lock. */
 /* the next printk record to read by syslog(READ) or /proc/kmsg */

diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
index 4995c078cff98d69af3add847adf1616bff717f7..a001e1e7a99269c9968059a00cff25ea496dbc99 100644 (file)
--- a/kernel/rcu/tree_stall.h
+++ b/kernel/rcu/tree_stall.h
@@ -647,7 +647,6 @@ static void print_cpu_stall(unsigned long gps)
         * See Documentation/RCU/stallwarn.rst for info on how to debug
         * RCU CPU stall warnings.
         */
-       printk_prefer_direct_enter();
        trace_rcu_stall_warning(rcu_state.name, TPS("SelfDetected"));
        pr_err("INFO: %s self-detected stall on CPU\n", rcu_state.name);
        raw_spin_lock_irqsave_rcu_node(rdp->mynode, flags);
@@ -685,7 +684,6 @@ static void print_cpu_stall(unsigned long gps)
         */
        set_tsk_need_resched(current);
        set_preempt_need_resched();
-       printk_prefer_direct_exit();
 }
 
 static void check_cpu_stall(struct rcu_data *rdp)

diff --git a/kernel/reboot.c b/kernel/reboot.c
index 4177645e74d6af001695d4443fc5d288e67a7ca3..6bcc5d6a6572b7decf4b731d9f130374555bf7d5 100644 (file)
--- a/kernel/reboot.c
+++ b/kernel/reboot.c
@@ -447,11 +447,9 @@ static int __orderly_reboot(void)
        ret = run_cmd(reboot_cmd);
 
        if (ret) {
-               printk_prefer_direct_enter();
                pr_warn("Failed to start orderly reboot: forcing the issue\n");
                emergency_sync();
                kernel_restart(NULL);
-               printk_prefer_direct_exit();
        }
 
        return ret;
@@ -464,7 +462,6 @@ static int __orderly_poweroff(bool force)
        ret = run_cmd(poweroff_cmd);
 
        if (ret && force) {
-               printk_prefer_direct_enter();
                pr_warn("Failed to start orderly shutdown: forcing the issue\n");
 
                /*
@@ -474,7 +471,6 @@ static int __orderly_poweroff(bool force)
                 */
                emergency_sync();
                kernel_power_off();
-               printk_prefer_direct_exit();
        }
 
        return ret;
@@ -532,8 +528,6 @@ EXPORT_SYMBOL_GPL(orderly_reboot);
  */
 static void hw_failure_emergency_poweroff_func(struct work_struct *work)
 {
-       printk_prefer_direct_enter();
-
        /*
         * We have reached here after the emergency shutdown waiting period has
         * expired. This means orderly_poweroff has not been able to shut off
@@ -550,8 +544,6 @@ static void hw_failure_emergency_poweroff_func(struct work_struct *work)
         */
        pr_emerg("Hardware protection shutdown failed. Trying emergency restart\n");
        emergency_restart();
-
-       printk_prefer_direct_exit();
 }
 
 static DECLARE_DELAYED_WORK(hw_failure_emergency_poweroff_work,
@@ -590,13 +582,11 @@ void hw_protection_shutdown(const char *reason, int ms_until_forced)
 {
        static atomic_t allow_proceed = ATOMIC_INIT(1);
 
-       printk_prefer_direct_enter();
-
        pr_emerg("HARDWARE PROTECTION shutdown (%s)\n", reason);
 
        /* Shutdown should be initiated only once. */
        if (!atomic_dec_and_test(&allow_proceed))
-               goto out;
+               return;
 
        /*
         * Queue a backup emergency shutdown in the event of
@@ -604,8 +594,6 @@ void hw_protection_shutdown(const char *reason, int ms_until_forced)
         */
        hw_failure_emergency_poweroff(ms_until_forced);
        orderly_poweroff(true);
-out:
-       printk_prefer_direct_exit();
 }
 EXPORT_SYMBOL_GPL(hw_protection_shutdown);
 

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 40024e03d42203833f7bfebfd9c754c26e77a255..9166220457bcbbf12852a591d617b442da3b2c37 100644 (file)
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -424,8 +424,6 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
                /* Start period for the next softlockup warning. */
                update_report_ts();
 
-               printk_prefer_direct_enter();
-
                pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
                        smp_processor_id(), duration,
                        current->comm, task_pid_nr(current));
@@ -444,8 +442,6 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
                add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK);
                if (softlockup_panic)
                        panic("softlockup: hung tasks");
-
-               printk_prefer_direct_exit();
        }
 
        return HRTIMER_RESTART;

diff --git a/kernel/watchdog_hld.c b/kernel/watchdog_hld.c
index 701f35f0e2d4499325202c6c7b7b592e590fc330..247bf0b1582ca1cf352f006aa1fd5f689f8f5859 100644 (file)
--- a/kernel/watchdog_hld.c
+++ b/kernel/watchdog_hld.c
@@ -135,8 +135,6 @@ static void watchdog_overflow_callback(struct perf_event *event,
                if (__this_cpu_read(hard_watchdog_warn) == true)
                        return;
 
-               printk_prefer_direct_enter();
-
                pr_emerg("Watchdog detected hard LOCKUP on cpu %d\n",
                         this_cpu);
                print_modules();
@@ -157,8 +155,6 @@ static void watchdog_overflow_callback(struct perf_event *event,
                if (hardlockup_panic)
                        nmi_panic(regs, "Hard LOCKUP");
 
-               printk_prefer_direct_exit();
-
                __this_cpu_write(hard_watchdog_warn, true);
                return;
        }