Orange Pi5 kernel

^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   1) // SPDX-License-Identifier: GPL-2.0-or-later
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   2) /*
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   3)  * printk_safe.c - Safe printk for printk-deadlock-prone contexts
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   4)  */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   5) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   6) #include <linux/preempt.h>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   7) #include <linux/spinlock.h>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   8) #include <linux/debug_locks.h>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   9) #include <linux/kdb.h>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  10) #include <linux/smp.h>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  11) #include <linux/cpumask.h>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  12) #include <linux/irq_work.h>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  13) #include <linux/printk.h>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  14) #include <linux/kprobes.h>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  15) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  16) #include "internal.h"
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  17) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  18) /*
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  19)  * printk() could not take logbuf_lock in NMI context. Instead,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  20)  * it uses an alternative implementation that temporary stores
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  21)  * the strings into a per-CPU buffer. The content of the buffer
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  22)  * is later flushed into the main ring buffer via IRQ work.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  23)  *
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  24)  * The alternative implementation is chosen transparently
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  25)  * by examining current printk() context mask stored in @printk_context
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  26)  * per-CPU variable.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  27)  *
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  28)  * The implementation allows to flush the strings also from another CPU.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  29)  * There are situations when we want to make sure that all buffers
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  30)  * were handled or when IRQs are blocked.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  31)  */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  32) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  33) #define SAFE_LOG_BUF_LEN ((1 << CONFIG_PRINTK_SAFE_LOG_BUF_SHIFT) -	\
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  34) 				sizeof(atomic_t) -			\
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  35) 				sizeof(atomic_t) -			\
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  36) 				sizeof(struct irq_work))
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  37) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  38) struct printk_safe_seq_buf {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  39) 	atomic_t		len;	/* length of written data */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  40) 	atomic_t		message_lost;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  41) 	struct irq_work		work;	/* IRQ work that flushes the buffer */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  42) 	unsigned char		buffer[SAFE_LOG_BUF_LEN];
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  43) };
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  44) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  45) static DEFINE_PER_CPU(struct printk_safe_seq_buf, safe_print_seq);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  46) static DEFINE_PER_CPU(int, printk_context);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  47) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  48) static DEFINE_RAW_SPINLOCK(safe_read_lock);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  49) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  50) #ifdef CONFIG_PRINTK_NMI
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  51) static DEFINE_PER_CPU(struct printk_safe_seq_buf, nmi_print_seq);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  52) #endif
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  53) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  54) /* Get flushed in a more safe context. */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  55) static void queue_flush_work(struct printk_safe_seq_buf *s)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  56) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  57) 	if (printk_percpu_data_ready())
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  58) 		irq_work_queue(&s->work);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  59) }
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  60) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  61) /*
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  62)  * Add a message to per-CPU context-dependent buffer. NMI and printk-safe
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  63)  * have dedicated buffers, because otherwise printk-safe preempted by
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  64)  * NMI-printk would have overwritten the NMI messages.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  65)  *
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  66)  * The messages are flushed from irq work (or from panic()), possibly,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  67)  * from other CPU, concurrently with printk_safe_log_store(). Should this
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  68)  * happen, printk_safe_log_store() will notice the buffer->len mismatch
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  69)  * and repeat the write.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  70)  */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  71) static __printf(2, 0) int printk_safe_log_store(struct printk_safe_seq_buf *s,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  72) 						const char *fmt, va_list args)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  73) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  74) 	int add;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  75) 	size_t len;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  76) 	va_list ap;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  77) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  78) again:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  79) 	len = atomic_read(&s->len);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  80) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  81) 	/* The trailing '\0' is not counted into len. */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  82) 	if (len >= sizeof(s->buffer) - 1) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  83) 		atomic_inc(&s->message_lost);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  84) 		queue_flush_work(s);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  85) 		return 0;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  86) 	}
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  87) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  88) 	/*
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  89) 	 * Make sure that all old data have been read before the buffer
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  90) 	 * was reset. This is not needed when we just append data.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  91) 	 */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  92) 	if (!len)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  93) 		smp_rmb();
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  94) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  95) 	va_copy(ap, args);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  96) 	add = vscnprintf(s->buffer + len, sizeof(s->buffer) - len, fmt, ap);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  97) 	va_end(ap);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  98) 	if (!add)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  99) 		return 0;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 100) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 101) 	/*
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 102) 	 * Do it once again if the buffer has been flushed in the meantime.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 103) 	 * Note that atomic_cmpxchg() is an implicit memory barrier that
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 104) 	 * makes sure that the data were written before updating s->len.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 105) 	 */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 106) 	if (atomic_cmpxchg(&s->len, len, len + add) != len)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 107) 		goto again;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 108) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 109) 	queue_flush_work(s);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 110) 	return add;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 111) }
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 112) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 113) static inline void printk_safe_flush_line(const char *text, int len)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 114) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 115) 	/*
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 116) 	 * Avoid any console drivers calls from here, because we may be
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 117) 	 * in NMI or printk_safe context (when in panic). The messages
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 118) 	 * must go only into the ring buffer at this stage.  Consoles will
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 119) 	 * get explicitly called later when a crashdump is not generated.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 120) 	 */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 121) 	printk_deferred("%.*s", len, text);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 122) }
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 123) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 124) /* printk part of the temporary buffer line by line */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 125) static int printk_safe_flush_buffer(const char *start, size_t len)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 126) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 127) 	const char *c, *end;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 128) 	bool header;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 129) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 130) 	c = start;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 131) 	end = start + len;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 132) 	header = true;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 133) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 134) 	/* Print line by line. */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 135) 	while (c < end) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 136) 		if (*c == '\n') {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 137) 			printk_safe_flush_line(start, c - start + 1);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 138) 			start = ++c;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 139) 			header = true;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 140) 			continue;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 141) 		}
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 142) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 143) 		/* Handle continuous lines or missing new line. */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 144) 		if ((c + 1 < end) && printk_get_level(c)) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 145) 			if (header) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 146) 				c = printk_skip_level(c);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 147) 				continue;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 148) 			}
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 149) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 150) 			printk_safe_flush_line(start, c - start);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 151) 			start = c++;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 152) 			header = true;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 153) 			continue;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 154) 		}
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 155) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 156) 		header = false;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 157) 		c++;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 158) 	}
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 159) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 160) 	/* Check if there was a partial line. Ignore pure header. */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 161) 	if (start < end && !header) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 162) 		static const char newline[] = KERN_CONT "\n";
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 163) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 164) 		printk_safe_flush_line(start, end - start);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 165) 		printk_safe_flush_line(newline, strlen(newline));
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 166) 	}
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 167) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 168) 	return len;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 169) }
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 170) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 171) static void report_message_lost(struct printk_safe_seq_buf *s)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 172) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 173) 	int lost = atomic_xchg(&s->message_lost, 0);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 174) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 175) 	if (lost)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 176) 		printk_deferred("Lost %d message(s)!\n", lost);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 177) }
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 178) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 179) /*
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 180)  * Flush data from the associated per-CPU buffer. The function
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 181)  * can be called either via IRQ work or independently.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 182)  */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 183) static void __printk_safe_flush(struct irq_work *work)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 184) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 185) 	struct printk_safe_seq_buf *s =
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 186) 		container_of(work, struct printk_safe_seq_buf, work);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 187) 	unsigned long flags;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 188) 	size_t len;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 189) 	int i;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 190) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 191) 	/*
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 192) 	 * The lock has two functions. First, one reader has to flush all
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 193) 	 * available message to make the lockless synchronization with
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 194) 	 * writers easier. Second, we do not want to mix messages from
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 195) 	 * different CPUs. This is especially important when printing
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 196) 	 * a backtrace.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 197) 	 */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 198) 	raw_spin_lock_irqsave(&safe_read_lock, flags);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 199) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 200) 	i = 0;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 201) more:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 202) 	len = atomic_read(&s->len);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 203) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 204) 	/*
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 205) 	 * This is just a paranoid check that nobody has manipulated
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 206) 	 * the buffer an unexpected way. If we printed something then
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 207) 	 * @len must only increase. Also it should never overflow the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 208) 	 * buffer size.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 209) 	 */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 210) 	if ((i && i >= len) || len > sizeof(s->buffer)) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 211) 		const char *msg = "printk_safe_flush: internal error\n";
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 212) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 213) 		printk_safe_flush_line(msg, strlen(msg));
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 214) 		len = 0;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 215) 	}
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 216) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 217) 	if (!len)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 218) 		goto out; /* Someone else has already flushed the buffer. */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 219) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 220) 	/* Make sure that data has been written up to the @len */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 221) 	smp_rmb();
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 222) 	i += printk_safe_flush_buffer(s->buffer + i, len - i);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 223) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 224) 	/*
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 225) 	 * Check that nothing has got added in the meantime and truncate
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 226) 	 * the buffer. Note that atomic_cmpxchg() is an implicit memory
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 227) 	 * barrier that makes sure that the data were copied before
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 228) 	 * updating s->len.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 229) 	 */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 230) 	if (atomic_cmpxchg(&s->len, len, 0) != len)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 231) 		goto more;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 232) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 233) out:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 234) 	report_message_lost(s);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 235) 	raw_spin_unlock_irqrestore(&safe_read_lock, flags);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 236) }
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 237) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 238) /**
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 239)  * printk_safe_flush - flush all per-cpu nmi buffers.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 240)  *
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 241)  * The buffers are flushed automatically via IRQ work. This function
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 242)  * is useful only when someone wants to be sure that all buffers have
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 243)  * been flushed at some point.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 244)  */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 245) void printk_safe_flush(void)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 246) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 247) 	int cpu;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 248) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 249) 	for_each_possible_cpu(cpu) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 250) #ifdef CONFIG_PRINTK_NMI
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 251) 		__printk_safe_flush(&per_cpu(nmi_print_seq, cpu).work);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 252) #endif
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 253) 		__printk_safe_flush(&per_cpu(safe_print_seq, cpu).work);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 254) 	}
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 255) }
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 256) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 257) /**
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 258)  * printk_safe_flush_on_panic - flush all per-cpu nmi buffers when the system
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 259)  *	goes down.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 260)  *
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 261)  * Similar to printk_safe_flush() but it can be called even in NMI context when
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 262)  * the system goes down. It does the best effort to get NMI messages into
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 263)  * the main ring buffer.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 264)  *
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 265)  * Note that it could try harder when there is only one CPU online.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 266)  */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 267) void printk_safe_flush_on_panic(void)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 268) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 269) 	/*
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 270) 	 * Make sure that we could access the main ring buffer.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 271) 	 * Do not risk a double release when more CPUs are up.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 272) 	 */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 273) 	if (raw_spin_is_locked(&logbuf_lock)) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 274) 		if (num_online_cpus() > 1)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 275) 			return;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 276) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 277) 		debug_locks_off();
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 278) 		raw_spin_lock_init(&logbuf_lock);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 279) 	}
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 280) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 281) 	if (raw_spin_is_locked(&safe_read_lock)) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 282) 		if (num_online_cpus() > 1)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 283) 			return;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 284) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 285) 		debug_locks_off();
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 286) 		raw_spin_lock_init(&safe_read_lock);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 287) 	}
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 288) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 289) 	printk_safe_flush();
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 290) }
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 291) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 292) #ifdef CONFIG_PRINTK_NMI
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 293) /*
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 294)  * Safe printk() for NMI context. It uses a per-CPU buffer to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 295)  * store the message. NMIs are not nested, so there is always only
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 296)  * one writer running. But the buffer might get flushed from another
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 297)  * CPU, so we need to be careful.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 298)  */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 299) static __printf(1, 0) int vprintk_nmi(const char *fmt, va_list args)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 300) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 301) 	struct printk_safe_seq_buf *s = this_cpu_ptr(&nmi_print_seq);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 302) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 303) 	return printk_safe_log_store(s, fmt, args);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 304) }
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 305) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 306) void noinstr printk_nmi_enter(void)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 307) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 308) 	this_cpu_add(printk_context, PRINTK_NMI_CONTEXT_OFFSET);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 309) }
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 310) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 311) void noinstr printk_nmi_exit(void)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 312) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 313) 	this_cpu_sub(printk_context, PRINTK_NMI_CONTEXT_OFFSET);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 314) }
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 315) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 316) /*
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 317)  * Marks a code that might produce many messages in NMI context
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 318)  * and the risk of losing them is more critical than eventual
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 319)  * reordering.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 320)  *
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 321)  * It has effect only when called in NMI context. Then printk()
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 322)  * will try to store the messages into the main logbuf directly
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 323)  * and use the per-CPU buffers only as a fallback when the lock
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 324)  * is not available.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 325)  */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 326) void printk_nmi_direct_enter(void)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 327) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 328) 	if (this_cpu_read(printk_context) & PRINTK_NMI_CONTEXT_MASK)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 329) 		this_cpu_or(printk_context, PRINTK_NMI_DIRECT_CONTEXT_MASK);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 330) }
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 331) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 332) void printk_nmi_direct_exit(void)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 333) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 334) 	this_cpu_and(printk_context, ~PRINTK_NMI_DIRECT_CONTEXT_MASK);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 335) }
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 336) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 337) #else
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 338) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 339) static __printf(1, 0) int vprintk_nmi(const char *fmt, va_list args)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 340) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 341) 	return 0;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 342) }
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 343) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 344) #endif /* CONFIG_PRINTK_NMI */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 345) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 346) /*
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 347)  * Lock-less printk(), to avoid deadlocks should the printk() recurse
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 348)  * into itself. It uses a per-CPU buffer to store the message, just like
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 349)  * NMI.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 350)  */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 351) static __printf(1, 0) int vprintk_safe(const char *fmt, va_list args)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 352) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 353) 	struct printk_safe_seq_buf *s = this_cpu_ptr(&safe_print_seq);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 354) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 355) 	return printk_safe_log_store(s, fmt, args);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 356) }
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 357) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 358) /* Can be preempted by NMI. */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 359) void __printk_safe_enter(void)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 360) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 361) 	this_cpu_inc(printk_context);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 362) }
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 363) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 364) /* Can be preempted by NMI. */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 365) void __printk_safe_exit(void)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 366) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 367) 	this_cpu_dec(printk_context);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 368) }
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 369) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 370) __printf(1, 0) int vprintk_func(const char *fmt, va_list args)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 371) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 372) #ifdef CONFIG_KGDB_KDB
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 373) 	/* Allow to pass printk() to kdb but avoid a recursion. */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 374) 	if (unlikely(kdb_trap_printk && kdb_printf_cpu < 0))
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 375) 		return vkdb_printf(KDB_MSGSRC_PRINTK, fmt, args);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 376) #endif
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 377) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 378) 	/*
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 379) 	 * Try to use the main logbuf even in NMI. But avoid calling console
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 380) 	 * drivers that might have their own locks.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 381) 	 */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 382) 	if ((this_cpu_read(printk_context) & PRINTK_NMI_DIRECT_CONTEXT_MASK) &&
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 383) 	    raw_spin_trylock(&logbuf_lock)) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 384) 		int len;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 385) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 386) 		len = vprintk_store(0, LOGLEVEL_DEFAULT, NULL, fmt, args);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 387) 		raw_spin_unlock(&logbuf_lock);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 388) 		defer_console_output();
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 389) 		return len;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 390) 	}
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 391) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 392) 	/* Use extra buffer in NMI when logbuf_lock is taken or in safe mode. */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 393) 	if (this_cpu_read(printk_context) & PRINTK_NMI_CONTEXT_MASK)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 394) 		return vprintk_nmi(fmt, args);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 395) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 396) 	/* Use extra buffer to prevent a recursion deadlock in safe mode. */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 397) 	if (this_cpu_read(printk_context) & PRINTK_SAFE_CONTEXT_MASK)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 398) 		return vprintk_safe(fmt, args);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 399) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 400) 	/* No obstacles. */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 401) 	return vprintk_default(fmt, args);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 402) }
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 403) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 404) void __init printk_safe_init(void)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 405) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 406) 	int cpu;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 407) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 408) 	for_each_possible_cpu(cpu) {
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 409) 		struct printk_safe_seq_buf *s;
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 410) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 411) 		s = &per_cpu(safe_print_seq, cpu);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 412) 		init_irq_work(&s->work, __printk_safe_flush);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 413) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 414) #ifdef CONFIG_PRINTK_NMI
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 415) 		s = &per_cpu(nmi_print_seq, cpu);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 416) 		init_irq_work(&s->work, __printk_safe_flush);
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 417) #endif
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 418) 	}
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 419) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 420) 	/* Flush pending messages that did not have scheduled IRQ works. */
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 421) 	printk_safe_flush();
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 422) }