1 // SPDX-License-Identifier: GPL-2.0-or-later
3  * printk_safe.c - Safe printk for printk-deadlock-prone contexts
21  * the strings into a per-CPU buffer. The content of the buffer
26  * per-CPU variable.
28  * The implementation allows to flush the strings also from another CPU.
33 #define SAFE_LOG_BUF_LEN ((1 << CONFIG_PRINTK_SAFE_LOG_BUF_SHIFT) -	\
34 				sizeof(atomic_t) -			\
35 				sizeof(atomic_t) -			\
56 		irq_work_queue(&s->work);  in queue_flush_work()
60  * Add a message to per-CPU context-dependent buffer. NMI and printk-safe
61  * have dedicated buffers, because otherwise printk-safe preempted by
62  * NMI-printk would have overwritten the NMI messages.
65  * from other CPU, concurrently with printk_safe_log_store(). Should this
66  * happen, printk_safe_log_store() will notice the buffer->len mismatch
77 	len = atomic_read(&s->len);  in printk_safe_log_store()
80 	if (len >= sizeof(s->buffer) - 1) {  in printk_safe_log_store()
81 		atomic_inc(&s->message_lost);  in printk_safe_log_store()
94 	add = vscnprintf(s->buffer + len, sizeof(s->buffer) - len, fmt, ap);  in printk_safe_log_store()
102 	 * makes sure that the data were written before updating s->len.  in printk_safe_log_store()
104 	if (atomic_cmpxchg(&s->len, len, len + add) != len)  in printk_safe_log_store()
135 			printk_safe_flush_line(start, c - start + 1);  in printk_safe_flush_buffer()
148 			printk_safe_flush_line(start, c - start);  in printk_safe_flush_buffer()
162 		printk_safe_flush_line(start, end - start);  in printk_safe_flush_buffer()
171 	int lost = atomic_xchg(&s->message_lost, 0);  in report_message_lost()
178  * Flush data from the associated per-CPU buffer. The function
202 	len = atomic_read(&s->len);  in __printk_safe_flush()
210 	if ((i && i >= len) || len > sizeof(s->buffer)) {  in __printk_safe_flush()
222 	i += printk_safe_flush_buffer(s->buffer + i, len - i);  in __printk_safe_flush()
228 	 * updating s->len.  in __printk_safe_flush()
230 	if (atomic_cmpxchg(&s->len, len, 0) != len)  in __printk_safe_flush()
239  * printk_safe_flush - flush all per-cpu nmi buffers.
247 	int cpu;  in printk_safe_flush()  local
249 	for_each_possible_cpu(cpu) {  in printk_safe_flush()
251 		__printk_safe_flush(&per_cpu(nmi_print_seq, cpu).work);  in printk_safe_flush()
253 		__printk_safe_flush(&per_cpu(safe_print_seq, cpu).work);  in printk_safe_flush()
258  * printk_safe_flush_on_panic - flush all per-cpu nmi buffers when the system
265  * Note that it could try harder when there is only one CPU online.
286  * Safe printk() for NMI context. It uses a per-CPU buffer to
289  * CPU, so we need to be careful.
315  * and use the per-CPU buffers only as a fallback when the lock
339  * Lock-less printk(), to avoid deadlocks should the printk() recurse
340  * into itself. It uses a per-CPU buffer to store the message, just like
398 	int cpu;  in printk_safe_init()  local
400 	for_each_possible_cpu(cpu) {  in printk_safe_init()
403 		s = &per_cpu(safe_print_seq, cpu);  in printk_safe_init()
404 		init_irq_work(&s->work, __printk_safe_flush);  in printk_safe_init()
407 		s = &per_cpu(nmi_print_seq, cpu);  in printk_safe_init()
408 		init_irq_work(&s->work, __printk_safe_flush);  in printk_safe_init()