[PATCH 01/19] printk/nbcon: Use an enum to specify the required callback in console_is_usable()

Marcos Paulo de Souza
2025-12-27T22:37:49Z

The current usage of console_is_usable() is clumsy. The parameter
@use_atomic is boolean and thus not self-explanatory. The function is
called twice in situations when there are no-strict requirements.

Replace it with enum nbcon_write_cb which provides a more descriptive
values for all 3 situations: atomic, thread or any.

Note that console_is_usable() checks only NBCON_USE_ATOMIC because
.write_thread() callback is mandatory. But the other two values still
make sense because they describe the intention of the caller.

Suggested-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
---
arch/um/kernel/kmsg_dump.c | 3 ++-
include/linux/console.h | 20 +++++++++++++++++---
kernel/debug/kdb/kdb_io.c | 2 +-
kernel/printk/nbcon.c | 8 ++++----
kernel/printk/printk.c | 16 ++++++++--------
5 files changed, 32 insertions(+), 17 deletions(-)

diff --git a/arch/um/kernel/kmsg_dump.c b/arch/um/kernel/kmsg_dump.c
index fc0f543d1d8e..8ae38308b67c 100644
--- a/arch/um/kernel/kmsg_dump.c
+++ b/arch/um/kernel/kmsg_dump.c
@@ -31,7 +31,8 @@ static void kmsg_dumper_stdout(struct kmsg_dumper *dumper,
* expected to output the crash information.
*/
if (strcmp(con->name, "ttynull") != 0 &&
- console_is_usable(con, console_srcu_read_flags(con), true)) {
+ console_is_usable(con, console_srcu_read_flags(con),
+ NBCON_USE_ATOMIC)) {
break;
}
}
diff --git a/include/linux/console.h b/include/linux/console.h
index fc9f5c5c1b04..35c03fc4ed51 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h
@@ -202,6 +202,19 @@ enum cons_flags {
CON_NBCON_ATOMIC_UNSAFE = BIT(9),
};

+/**
+ * enum nbcon_write_cb - Defines which nbcon write() callback must be used based
+ * on the caller context.
+ * @NBCON_USE_ATOMIC: Use con->write_atomic().
+ * @NBCON_USE_THREAD: Use con->write_thread().
+ * @NBCON_USE_ANY: The caller does not have any strict requirements.
+ */
+enum nbcon_write_cb {
+ NBCON_USE_ATOMIC,
+ NBCON_USE_THREAD,
+ NBCON_USE_ANY,
+};
+
/**
* struct nbcon_state - console state for nbcon consoles
* @atom: Compound of the state fields for atomic operations
@@ -622,7 +635,8 @@ extern void nbcon_kdb_release(struct nbcon_write_context *wctxt);
* which can also play a role in deciding if @con can be used to print
* records.
*/
-static inline bool console_is_usable(struct console *con, short flags, bool use_atomic)
+static inline bool console_is_usable(struct console *con, short flags,
+ enum nbcon_write_cb nwc)
{
if (!(flags & CON_ENABLED))
return false;
@@ -631,7 +645,7 @@ static inline bool console_is_usable(struct console *con, short flags, bool use_
return false;

if (flags & CON_NBCON) {
- if (use_atomic) {
+ if (nwc & NBCON_USE_ATOMIC) {
/* The write_atomic() callback is optional. */
if (!con->write_atomic)
return false;
@@ -679,7 +693,7 @@ static inline bool nbcon_kdb_try_acquire(struct console *con,
struct nbcon_write_context *wctxt) { return false; }
static inline void nbcon_kdb_release(struct nbcon_write_context *wctxt) { }
static inline bool console_is_usable(struct console *con, short flags,
- bool use_atomic) { return false; }
+ enum nbcon_write_cb nwc) { return false; }
#endif

extern int console_set_on_cmdline;
diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c
index 61c1690058ed..6ffb962392a4 100644
--- a/kernel/debug/kdb/kdb_io.c
+++ b/kernel/debug/kdb/kdb_io.c
@@ -591,7 +591,7 @@ static void kdb_msg_write(const char *msg, int msg_len)
for_each_console_srcu(c) {
short flags = console_srcu_read_flags(c);

- if (!console_is_usable(c, flags, true))
+ if (!console_is_usable(c, flags, NBCON_USE_ATOMIC))
continue;
if (c == dbg_io_ops->cons)
continue;
diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
index be5a04367e60..13865ef85990 100644
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -1184,7 +1184,7 @@ static bool nbcon_kthread_should_wakeup(struct console *con, struct nbcon_contex
cookie = console_srcu_read_lock();

flags = console_srcu_read_flags(con);
- if (console_is_usable(con, flags, false)) {
+ if (console_is_usable(con, flags, NBCON_USE_THREAD)) {
/* Bring the sequence in @ctxt up to date */
ctxt->seq = nbcon_seq_read(con);

@@ -1251,7 +1251,7 @@ static int nbcon_kthread_func(void *__console)

con_flags = console_srcu_read_flags(con);

- if (console_is_usable(con, con_flags, false))
+ if (console_is_usable(con, con_flags, NBCON_USE_THREAD))
backlog = nbcon_emit_one(&wctxt, false);

console_srcu_read_unlock(cookie);
@@ -1650,7 +1650,7 @@ static void __nbcon_atomic_flush_pending(u64 stop_seq)
if (!(flags & CON_NBCON))
continue;

- if (!console_is_usable(con, flags, true))
+ if (!console_is_usable(con, flags, NBCON_USE_ATOMIC))
continue;

if (nbcon_seq_read(con) >= stop_seq)
@@ -1904,7 +1904,7 @@ void nbcon_device_release(struct console *con)
*/
cookie = console_srcu_read_lock();
printk_get_console_flush_type(&ft);
- if (console_is_usable(con, console_srcu_read_flags(con), true) &&
+ if (console_is_usable(con, console_srcu_read_flags(con), NBCON_USE_ATOMIC) &&
!ft.nbcon_offload &&
prb_read_valid(prb, nbcon_seq_read(con), NULL)) {
/*
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 7394f1b6033b..5f4b84f9562e 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3203,7 +3203,9 @@ static bool console_flush_one_record(bool do_cond_resched, u64 *next_seq, bool *
if ((flags & CON_NBCON) && (ft.nbcon_atomic || ft.nbcon_offload))
continue;

- if (!console_is_usable(con, flags, !do_cond_resched))
+ if (!console_is_usable(con, flags,
+ do_cond_resched ? NBCON_USE_THREAD
+ : NBCON_USE_ATOMIC))
continue;
any_usable = true;

@@ -3392,7 +3394,7 @@ void console_unblank(void)
*/
cookie = console_srcu_read_lock();
for_each_console_srcu(c) {
- if (!console_is_usable(c, console_srcu_read_flags(c), true))
+ if (!console_is_usable(c, console_srcu_read_flags(c), NBCON_USE_ATOMIC))
continue;

if (c->unblank) {
@@ -3432,7 +3434,7 @@ void console_unblank(void)

cookie = console_srcu_read_lock();
for_each_console_srcu(c) {
- if (!console_is_usable(c, console_srcu_read_flags(c), true))
+ if (!console_is_usable(c, console_srcu_read_flags(c), NBCON_USE_ATOMIC))
continue;

if (c->unblank)
@@ -3633,7 +3635,7 @@ static bool legacy_kthread_should_wakeup(void)
if ((flags & CON_NBCON) && (ft.nbcon_atomic || ft.nbcon_offload))
continue;

- if (!console_is_usable(con, flags, false))
+ if (!console_is_usable(con, flags, NBCON_USE_THREAD))
continue;

if (flags & CON_NBCON) {
@@ -4204,7 +4206,7 @@ static int unregister_console_locked(struct console *console)

if (!console_is_registered_locked(console))
res = -ENODEV;
- else if (console_is_usable(console, console->flags, true))
+ else if (console_is_usable(console, console->flags, NBCON_USE_ATOMIC))
__pr_flush(console, 1000, true);

/* Disable it unconditionally */
@@ -4485,10 +4487,8 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
* that they make forward progress, so only increment
* @diff for usable consoles.
*/
- if (!console_is_usable(c, flags, true) &&
- !console_is_usable(c, flags, false)) {
+ if (!console_is_usable(c, flags, NBCON_USE_ANY))
continue;
- }

if (flags & CON_NBCON) {
printk_seq = nbcon_seq_read(c);

--
2.52.0