printk: nbcon: Use thread callback if in task context for legacy
When printing via console_lock, the write_atomic() callback is used for nbcon consoles. However, if it is known that the current context is a task context, the write_thread() callback can be used instead. Using write_thread() instead of write_atomic() helps to reduce large disabled preemption regions when the device_lock does not disable preemption. This is mainly a preparatory change to allow avoiding write_atomic() completely during normal operation if boot consoles are registered. As a side-effect, it also allows consolidating the printing code for legacy printing and the kthread printer. Signed-off-by: John Ogness <john.ogness@linutronix.de> Reviewed-by: Petr Mladek <pmladek@suse.com> Link: https://lore.kernel.org/r/20240904120536.115780-9-john.ogness@linutronix.de Signed-off-by: Petr Mladek <pmladek@suse.com>
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@ -90,7 +90,7 @@ void nbcon_free(struct console *con);
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enum nbcon_prio nbcon_get_default_prio(void);
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void nbcon_atomic_flush_pending(void);
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bool nbcon_legacy_emit_next_record(struct console *con, bool *handover,
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int cookie);
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int cookie, bool use_atomic);
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bool nbcon_kthread_create(struct console *con);
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void nbcon_kthread_stop(struct console *con);
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void nbcon_kthreads_wake(void);
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@ -174,7 +174,7 @@ static inline void nbcon_free(struct console *con) { }
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static inline enum nbcon_prio nbcon_get_default_prio(void) { return NBCON_PRIO_NONE; }
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static inline void nbcon_atomic_flush_pending(void) { }
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static inline bool nbcon_legacy_emit_next_record(struct console *con, bool *handover,
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int cookie) { return false; }
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int cookie, bool use_atomic) { return false; }
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static inline void nbcon_kthread_wake(struct console *con) { }
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static inline bool console_is_usable(struct console *con, short flags,
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@ -1043,9 +1043,10 @@ update_con:
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}
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/*
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* nbcon_atomic_emit_one - Print one record for an nbcon console using the
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* write_atomic() callback
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* nbcon_emit_one - Print one record for an nbcon console using the
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* specified callback
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* @wctxt: An initialized write context struct to use for this context
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* @use_atomic: True if the write_atomic() callback is to be used
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*
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* Return: True, when a record has been printed and there are still
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* pending records. The caller might want to continue flushing.
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@ -1058,12 +1059,25 @@ update_con:
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* This is an internal helper to handle the locking of the console before
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* calling nbcon_emit_next_record().
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*/
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static bool nbcon_atomic_emit_one(struct nbcon_write_context *wctxt)
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static bool nbcon_emit_one(struct nbcon_write_context *wctxt, bool use_atomic)
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{
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struct nbcon_context *ctxt = &ACCESS_PRIVATE(wctxt, ctxt);
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struct console *con = ctxt->console;
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unsigned long flags;
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bool ret = false;
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if (!use_atomic) {
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con->device_lock(con, &flags);
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/*
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* Ensure this stays on the CPU to make handover and
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* takeover possible.
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*/
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cant_migrate();
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}
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if (!nbcon_context_try_acquire(ctxt))
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return false;
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goto out;
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/*
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* nbcon_emit_next_record() returns false when the console was
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@ -1073,12 +1087,16 @@ static bool nbcon_atomic_emit_one(struct nbcon_write_context *wctxt)
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* The higher priority printing context takes over responsibility
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* to print the pending records.
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*/
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if (!nbcon_emit_next_record(wctxt, true))
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return false;
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if (!nbcon_emit_next_record(wctxt, use_atomic))
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goto out;
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nbcon_context_release(ctxt);
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return ctxt->backlog;
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ret = ctxt->backlog;
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out:
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if (!use_atomic)
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con->device_unlock(con, flags);
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return ret;
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}
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/**
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@ -1163,30 +1181,8 @@ wait_for_event:
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con_flags = console_srcu_read_flags(con);
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if (console_is_usable(con, con_flags, false)) {
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unsigned long lock_flags;
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con->device_lock(con, &lock_flags);
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/*
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* Ensure this stays on the CPU to make handover and
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* takeover possible.
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*/
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cant_migrate();
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if (nbcon_context_try_acquire(ctxt)) {
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/*
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* If the emit fails, this context is no
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* longer the owner.
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*/
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if (nbcon_emit_next_record(&wctxt, false)) {
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nbcon_context_release(ctxt);
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backlog = ctxt->backlog;
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}
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}
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con->device_unlock(con, lock_flags);
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}
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if (console_is_usable(con, con_flags, false))
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backlog = nbcon_emit_one(&wctxt, false);
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console_srcu_read_unlock(cookie);
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@ -1367,6 +1363,13 @@ enum nbcon_prio nbcon_get_default_prio(void)
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* both the console_lock and the SRCU read lock. Otherwise it
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* is set to false.
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* @cookie: The cookie from the SRCU read lock.
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* @use_atomic: Set true when called in an atomic or unknown context.
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* It affects which nbcon callback will be used: write_atomic()
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* or write_thread().
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*
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* When false, the write_thread() callback is used and would be
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* called in a preemtible context unless disabled by the
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* device_lock. The legacy handover is not allowed in this mode.
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*
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* Context: Any context except NMI.
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* Return: True, when a record has been printed and there are still
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@ -1382,26 +1385,36 @@ enum nbcon_prio nbcon_get_default_prio(void)
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* Essentially it is the nbcon version of console_emit_next_record().
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*/
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bool nbcon_legacy_emit_next_record(struct console *con, bool *handover,
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int cookie)
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int cookie, bool use_atomic)
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{
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struct nbcon_write_context wctxt = { };
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struct nbcon_context *ctxt = &ACCESS_PRIVATE(&wctxt, ctxt);
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unsigned long flags;
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bool progress;
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/* Use the same procedure as console_emit_next_record(). */
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printk_safe_enter_irqsave(flags);
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console_lock_spinning_enable();
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stop_critical_timings();
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ctxt->console = con;
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ctxt->prio = nbcon_get_default_prio();
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progress = nbcon_atomic_emit_one(&wctxt);
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if (use_atomic) {
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/*
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* In an atomic or unknown context, use the same procedure as
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* in console_emit_next_record(). It allows to handover.
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*/
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printk_safe_enter_irqsave(flags);
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console_lock_spinning_enable();
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stop_critical_timings();
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}
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progress = nbcon_emit_one(&wctxt, use_atomic);
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if (use_atomic) {
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start_critical_timings();
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*handover = console_lock_spinning_disable_and_check(cookie);
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printk_safe_exit_irqrestore(flags);
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} else {
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/* Non-atomic does not perform legacy spinning handovers. */
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*handover = false;
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}
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return progress;
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}
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@ -3077,12 +3077,13 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove
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u64 printk_seq;
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bool progress;
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if (!console_is_usable(con, flags, true))
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if (!console_is_usable(con, flags, !do_cond_resched))
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continue;
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any_usable = true;
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if (flags & CON_NBCON) {
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progress = nbcon_legacy_emit_next_record(con, handover, cookie);
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progress = nbcon_legacy_emit_next_record(con, handover, cookie,
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!do_cond_resched);
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printk_seq = nbcon_seq_read(con);
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} else {
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progress = console_emit_next_record(con, handover, cookie);
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