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printk: Add per-console suspended state
Currently the global @console_suspended is used to determine if consoles are in a suspended state. Its primary purpose is to allow usage of the console_lock when suspended without causing console printing. It is synchronized by the console_lock. Rather than relying on the console_lock to determine suspended state, make it an official per-console state that is set within console->flags. This allows the state to be queried via SRCU. Remove @console_suspended. Console printing will still be avoided when suspended because console_is_usable() returns false when the new suspended flag is set for that console. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org> Reviewed-by: Petr Mladek <pmladek@suse.com> Signed-off-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20230717194607.145135-7-john.ogness@linutronix.de
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@ -154,6 +154,8 @@ static inline int con_debug_leave(void)
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* receiving the printk spam for obvious reasons.
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* @CON_EXTENDED: The console supports the extended output format of
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* /dev/kmesg which requires a larger output buffer.
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* @CON_SUSPENDED: Indicates if a console is suspended. If true, the
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* printing callbacks must not be called.
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*/
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enum cons_flags {
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CON_PRINTBUFFER = BIT(0),
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@ -163,6 +165,7 @@ enum cons_flags {
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CON_ANYTIME = BIT(4),
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CON_BRL = BIT(5),
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CON_EXTENDED = BIT(6),
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CON_SUSPENDED = BIT(7),
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};
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/**
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@ -86,7 +86,7 @@ EXPORT_SYMBOL(oops_in_progress);
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static DEFINE_MUTEX(console_mutex);
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/*
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* console_sem protects updates to console->seq and console_suspended,
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* console_sem protects updates to console->seq
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* and also provides serialization for console printing.
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*/
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static DEFINE_SEMAPHORE(console_sem);
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@ -359,7 +359,7 @@ static bool panic_in_progress(void)
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* paths in the console code where we end up in places I want
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* locked without the console semaphore held).
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*/
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static int console_locked, console_suspended;
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static int console_locked;
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/*
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* Array of consoles built from command line options (console=)
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@ -2549,22 +2549,46 @@ MODULE_PARM_DESC(console_no_auto_verbose, "Disable console loglevel raise to hig
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*/
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void suspend_console(void)
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{
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struct console *con;
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if (!console_suspend_enabled)
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return;
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pr_info("Suspending console(s) (use no_console_suspend to debug)\n");
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pr_flush(1000, true);
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console_lock();
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console_suspended = 1;
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up_console_sem();
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console_list_lock();
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for_each_console(con)
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console_srcu_write_flags(con, con->flags | CON_SUSPENDED);
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console_list_unlock();
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/*
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* Ensure that all SRCU list walks have completed. All printing
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* contexts must be able to see that they are suspended so that it
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* is guaranteed that all printing has stopped when this function
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* completes.
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*/
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synchronize_srcu(&console_srcu);
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}
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void resume_console(void)
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{
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struct console *con;
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if (!console_suspend_enabled)
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return;
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down_console_sem();
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console_suspended = 0;
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console_unlock();
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console_list_lock();
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for_each_console(con)
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console_srcu_write_flags(con, con->flags & ~CON_SUSPENDED);
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console_list_unlock();
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/*
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* Ensure that all SRCU list walks have completed. All printing
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* contexts must be able to see they are no longer suspended so
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* that they are guaranteed to wake up and resume printing.
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*/
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synchronize_srcu(&console_srcu);
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pr_flush(1000, true);
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}
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@ -2623,8 +2647,6 @@ void console_lock(void)
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msleep(1000);
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down_console_sem();
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if (console_suspended)
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return;
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console_locked = 1;
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console_may_schedule = 1;
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}
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@ -2645,10 +2667,6 @@ int console_trylock(void)
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return 0;
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if (down_trylock_console_sem())
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return 0;
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if (console_suspended) {
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up_console_sem();
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return 0;
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}
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console_locked = 1;
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console_may_schedule = 0;
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return 1;
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@ -2674,6 +2692,9 @@ static inline bool console_is_usable(struct console *con)
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if (!(flags & CON_ENABLED))
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return false;
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if ((flags & CON_SUSPENDED))
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return false;
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if (!con->write)
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return false;
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@ -2992,11 +3013,6 @@ void console_unlock(void)
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bool flushed;
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u64 next_seq;
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if (console_suspended) {
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up_console_sem();
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return;
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}
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/*
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* Console drivers are called with interrupts disabled, so
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* @console_may_schedule should be cleared before; however, we may
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@ -3726,8 +3742,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
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/*
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* Hold the console_lock to guarantee safe access to
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* console->seq and to prevent changes to @console_suspended
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* until all consoles have been processed.
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* console->seq.
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*/
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console_lock();
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@ -3735,6 +3750,11 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
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for_each_console_srcu(c) {
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if (con && con != c)
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continue;
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/*
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* If consoles are not usable, it cannot be expected
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* that they make forward progress, so only increment
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* @diff for usable consoles.
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*/
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if (!console_is_usable(c))
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continue;
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printk_seq = c->seq;
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@ -3743,18 +3763,12 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
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}
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console_srcu_read_unlock(cookie);
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/*
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* If consoles are suspended, it cannot be expected that they
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* make forward progress, so timeout immediately. @diff is
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* still used to return a valid flush status.
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*/
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if (console_suspended)
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remaining = 0;
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else if (diff != last_diff && reset_on_progress)
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if (diff != last_diff && reset_on_progress)
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remaining = timeout_ms;
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console_unlock();
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/* Note: @diff is 0 if there are no usable consoles. */
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if (diff == 0 || remaining == 0)
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break;
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@ -3788,7 +3802,7 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
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* printer has been seen to make some forward progress.
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*
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* Context: Process context. May sleep while acquiring console lock.
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* Return: true if all enabled printers are caught up.
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* Return: true if all usable printers are caught up.
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*/
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static bool pr_flush(int timeout_ms, bool reset_on_progress)
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{
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