Commit 5dde3b73 authored by John Ogness's avatar John Ogness Committed by Petr Mladek
Browse files

printk: nbcon: Add unsafe flushing on panic 



Add nbcon_atomic_flush_unsafe() to flush all nbcon consoles
using the write_atomic() callback and allowing unsafe hostile
takeovers. Call this at the end of panic() as a final attempt
to flush any pending messages.

Note that legacy consoles use unsafe methods for flushing
from the beginning of panic (see bust_spinlocks()). Therefore,
systems using both legacy and nbcon consoles may still fail to
see panic messages due to unsafe legacy console usage.

Signed-off-by: default avatarJohn Ogness <john.ogness@linutronix.de>
Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20240820063001.36405-27-john.ogness@linutronix.de


Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
parent d2e85ca7

include/linux/printk.h

+5 −0
Original line number Diff line number Diff line
@@ -202,6 +202,7 @@ void printk_trigger_flush(void); 
void console_try_replay_all(void);

extern bool nbcon_device_try_acquire(struct console *con);

extern void nbcon_device_release(struct console *con);

void nbcon_atomic_flush_unsafe(void);

#else

static inline __printf(1, 0)

int vprintk(const char *s, va_list args)
@@ -294,6 +295,10 @@ static inline void nbcon_device_release(struct console *con) 
{

}



static inline void nbcon_atomic_flush_unsafe(void)

{

}



#endif



bool this_cpu_in_panic(void);

kernel/panic.c

+1 −0
Original line number Diff line number Diff line
@@ -463,6 +463,7 @@ void panic(const char *fmt, ...) 
	 * Explicitly flush the kernel log buffer one last time.

	 */

	console_flush_on_panic(CONSOLE_FLUSH_PENDING);

	nbcon_atomic_flush_unsafe();



	local_irq_enable();

	for (i = 0; ; i += PANIC_TIMER_STEP) {

kernel/printk/nbcon.c

+25 −7
Original line number Diff line number Diff line
@@ -1083,6 +1083,7 @@ bool nbcon_legacy_emit_next_record(struct console *con, bool *handover, 
 *					write_atomic() callback

 * @con:			The nbcon console to flush

 * @stop_seq:			Flush up until this record

 * @allow_unsafe_takeover:	True, to allow unsafe hostile takeovers

 *

 * Return:	0 if @con was flushed up to @stop_seq Otherwise, error code on

 *		failure.
@@ -1101,7 +1102,8 @@ bool nbcon_legacy_emit_next_record(struct console *con, bool *handover, 
 * returned, it cannot be expected that the unfinalized record will become

 * available.

 */

static int __nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq)

static int __nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq,

					    bool allow_unsafe_takeover)

{

	struct nbcon_write_context wctxt = { };

	struct nbcon_context *ctxt = &ACCESS_PRIVATE(&wctxt, ctxt);
@@ -1110,6 +1112,7 @@ static int __nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq) 
	ctxt->console			= con;

	ctxt->spinwait_max_us		= 2000;

	ctxt->prio			= nbcon_get_default_prio();

	ctxt->allow_unsafe_takeover	= allow_unsafe_takeover;



	if (!nbcon_context_try_acquire(ctxt))

		return -EPERM;
@@ -1140,13 +1143,15 @@ static int __nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq) 
 *					write_atomic() callback

 * @con:			The nbcon console to flush

 * @stop_seq:			Flush up until this record

 * @allow_unsafe_takeover:	True, to allow unsafe hostile takeovers

 *

 * This will stop flushing before @stop_seq if another context has ownership.

 * That context is then responsible for the flushing. Likewise, if new records

 * are added while this context was flushing and there is no other context

 * to handle the printing, this context must also flush those records.

 */

static void nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq)

static void nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq,

					   bool allow_unsafe_takeover)

{

	unsigned long flags;

	int err;
@@ -1160,7 +1165,7 @@ static void nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq) 
	 */

	local_irq_save(flags);



	err = __nbcon_atomic_flush_pending_con(con, stop_seq);

	err = __nbcon_atomic_flush_pending_con(con, stop_seq, allow_unsafe_takeover);



	local_irq_restore(flags);
@@ -1190,8 +1195,9 @@ static void nbcon_atomic_flush_pending_con(struct console *con, u64 stop_seq) 
 * __nbcon_atomic_flush_pending - Flush all nbcon consoles using their

 *					write_atomic() callback

 * @stop_seq:			Flush up until this record

 * @allow_unsafe_takeover:	True, to allow unsafe hostile takeovers

 */

static void __nbcon_atomic_flush_pending(u64 stop_seq)

static void __nbcon_atomic_flush_pending(u64 stop_seq, bool allow_unsafe_takeover)

{

	struct console *con;

	int cookie;
@@ -1209,7 +1215,7 @@ static void __nbcon_atomic_flush_pending(u64 stop_seq) 
		if (nbcon_seq_read(con) >= stop_seq)

			continue;



		nbcon_atomic_flush_pending_con(con, stop_seq);

		nbcon_atomic_flush_pending_con(con, stop_seq, allow_unsafe_takeover);

	}

	console_srcu_read_unlock(cookie);

}
@@ -1225,7 +1231,19 @@ static void __nbcon_atomic_flush_pending(u64 stop_seq) 
 */

void nbcon_atomic_flush_pending(void)

{

	__nbcon_atomic_flush_pending(prb_next_reserve_seq(prb));

	__nbcon_atomic_flush_pending(prb_next_reserve_seq(prb), false);

}



/**

 * nbcon_atomic_flush_unsafe - Flush all nbcon consoles using their

 *	write_atomic() callback and allowing unsafe hostile takeovers

 *

 * Flush the backlog up through the currently newest record. Unsafe hostile

 * takeovers will be performed, if necessary.

 */

void nbcon_atomic_flush_unsafe(void)

{

	__nbcon_atomic_flush_pending(prb_next_reserve_seq(prb), true);

}



/**
@@ -1342,7 +1360,7 @@ void nbcon_device_release(struct console *con) 
	if (console_is_usable(con, console_srcu_read_flags(con)) &&

	    prb_read_valid(prb, nbcon_seq_read(con), NULL)) {

		if (!have_boot_console) {

			__nbcon_atomic_flush_pending_con(con, prb_next_reserve_seq(prb));

			__nbcon_atomic_flush_pending_con(con, prb_next_reserve_seq(prb), false);

		} else if (!is_printk_legacy_deferred()) {

			if (console_trylock())

				console_unlock();