tracing/seq-buf/printk: New seq-buf utility from trace_seq for printk in NMI

new file mode 100644
index 000000000000..4f7a96a9d71a
@@ -0,0 +1,81 @@
+#ifndef _LINUX_SEQ_BUF_H
+#define _LINUX_SEQ_BUF_H
+
+#include <linux/fs.h>
+
+/*
+ * Trace sequences are used to allow a function to call several other functions
+ * to create a string of data to use.
+ */
+
+/**
+ * seq_buf - seq buffer structure
+ * @buffer:	pointer to the buffer
+ * @size:	size of the buffer
+ * @len:	the amount of data inside the buffer
+ * @readpos:	The next position to read in the buffer.
+ */
+struct seq_buf {
+	unsigned char		*buffer;
+	unsigned int		size;
+	unsigned int		len;
+	unsigned int		readpos;
+};
+
+static inline void
+seq_buf_init(struct seq_buf *s, unsigned char *buf, unsigned int size)
+{
+	s->buffer = buf;
+	s->size = size;
+	s->len = 0;
+	s->readpos = 0;
+}
+
+/*
+ * seq_buf have a buffer that might overflow. When this happens
+ * the len and size are set to be equal.
+ */
+static inline bool
+seq_buf_has_overflowed(struct seq_buf *s)
+{
+	return s->len == s->size;
+}
+
+static inline void
+seq_buf_set_overflow(struct seq_buf *s)
+{
+	s->len = s->size;
+}
+
+/*
+ * How much buffer is left on the seq_buf?
+ */
+static inline unsigned int
+seq_buf_buffer_left(struct seq_buf *s)
+{
+	if (seq_buf_has_overflowed(s))
+		return 0;
+
+	return (s->size - 1) - s->len;
+}
+
+extern __printf(2, 3)
+int seq_buf_printf(struct seq_buf *s, const char *fmt, ...);
+extern __printf(2, 0)
+int seq_buf_vprintf(struct seq_buf *s, const char *fmt, va_list args);
+extern int
+seq_buf_bprintf(struct seq_buf *s, const char *fmt, const u32 *binary);
+extern int seq_buf_print_seq(struct seq_file *m, struct seq_buf *s);
+extern int seq_buf_to_user(struct seq_buf *s, char __user *ubuf,
+			   int cnt);
+extern int seq_buf_puts(struct seq_buf *s, const char *str);
+extern int seq_buf_putc(struct seq_buf *s, unsigned char c);
+extern int seq_buf_putmem(struct seq_buf *s, const void *mem, unsigned int len);
+extern int seq_buf_putmem_hex(struct seq_buf *s, const void *mem,
+			      unsigned int len);
+extern int seq_buf_path(struct seq_buf *s, const struct path *path);
+
+extern int seq_buf_bitmask(struct seq_buf *s, const unsigned long *maskp,
+			   int nmaskbits);
+
+#endif /* _LINUX_SEQ_BUF_H */

index db8a73224f1a..85d37106be3d 100644
@@ -1,7 +1,7 @@
 #ifndef _LINUX_TRACE_SEQ_H
 #define _LINUX_TRACE_SEQ_H
 
-#include <linux/fs.h>
+#include <linux/seq_buf.h>
 
 #include <asm/page.h>
 

@@ -12,16 +12,14 @@
 
 struct trace_seq {
 	unsigned char		buffer[PAGE_SIZE];
-	unsigned int		len;
-	unsigned int		readpos;
+	struct seq_buf		seq;
 	int			full;
 };
 
 static inline void
 trace_seq_init(struct trace_seq *s)
 {
-	s->len = 0;
-	s->readpos = 0;
+	seq_buf_init(&s->seq, s->buffer, PAGE_SIZE);
 	s->full = 0;
 }
 

@@ -37,7 +35,7 @@ trace_seq_init(struct trace_seq *s)
 static inline unsigned char *
 trace_seq_buffer_ptr(struct trace_seq *s)
 {
-	return s->buffer + s->len;
+	return s->buffer + s->seq.len;
 }
 
 /**

@@ -49,7 +47,7 @@ trace_seq_buffer_ptr(struct trace_seq *s)
  */
 static inline bool trace_seq_has_overflowed(struct trace_seq *s)
 {
-	return s->full || s->len > PAGE_SIZE - 1;
+	return s->full || seq_buf_has_overflowed(&s->seq);
 }
 
 /*

341 lines not on this page · raw message

index 3ce3c4ccfc94..7d7a07e9b9e9 100644
@@ -939,19 +939,20 @@ out:
 	return ret;
 }
 
+/* TODO add a seq_buf_to_buffer() */
 static ssize_t trace_seq_to_buffer(struct trace_seq *s, void *buf, size_t cnt)
 {
 	int len;
 
-	if (s->len <= s->readpos)
+	if (s->seq.len <= s->seq.readpos)
 		return -EBUSY;
 
-	len = s->len - s->readpos;
+	len = s->seq.len - s->seq.readpos;
 	if (cnt > len)
 		cnt = len;
-	memcpy(buf, s->buffer + s->readpos, cnt);
+	memcpy(buf, s->buffer + s->seq.readpos, cnt);
 
-	s->readpos += cnt;
+	s->seq.readpos += cnt;
 	return cnt;
 }
 

@@ -4315,6 +4316,8 @@ static int tracing_open_pipe(struct inode *inode, struct file *filp)
 		goto out;
 	}
 
+	trace_seq_init(&iter->seq);
+
 	/*
 	 * We make a copy of the current tracer to avoid concurrent
 	 * changes on it while we are reading.

@@ -4511,18 +4514,18 @@ waitagain:
 	trace_access_lock(iter->cpu_file);
 	while (trace_find_next_entry_inc(iter) != NULL) {
 		enum print_line_t ret;
-		int len = iter->seq.len;
+		int len = iter->seq.seq.len;
 
 		ret = print_trace_line(iter);
 		if (ret == TRACE_TYPE_PARTIAL_LINE) {
 			/* don't print partial lines */
-			iter->seq.len = len;
+			iter->seq.seq.len = len;
 			break;
 		}
 		if (ret != TRACE_TYPE_NO_CONSUME)
 			trace_consume(iter);
 
-		if (iter->seq.len >= cnt)
+		if (iter->seq.seq.len >= cnt)
 			break;
 
 		/*

@@ -4538,7 +4541,7 @@ waitagain:
 
 	/* Now copy what we have to the user */
 	sret = trace_seq_to_user(&iter->seq, ubuf, cnt);
-	if (iter->seq.readpos >= iter->seq.len)
+	if (iter->seq.seq.readpos >= iter->seq.seq.len)
 		trace_seq_init(&iter->seq);
 
 	/*

@@ -4576,16 +4579,16 @@ tracing_fill_pipe_page(size_t rem, struct trace_iterator *iter)
 
 	/* Seq buffer is page-sized, exactly what we need. */
 	for (;;) {
-		count = iter->seq.len;
+		count = iter->seq.seq.len;
 		ret = print_trace_line(iter);
-		count = iter->seq.len - count;
+		count = iter->seq.seq.len - count;
 		if (rem < count) {
 			rem = 0;
-			iter->seq.len -= count;
+			iter->seq.seq.len -= count;
 			break;
 		}
 		if (ret == TRACE_TYPE_PARTIAL_LINE) {
-			iter->seq.len -= count;
+			iter->seq.seq.len -= count;
 			break;
 		}
 

@@ -4666,13 +4669,13 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
 		/* Copy the data into the page, so we can start over. */
 		ret = trace_seq_to_buffer(&iter->seq,
 					  page_address(spd.pages[i]),
-					  iter->seq.len);
+					  iter->seq.seq.len);
 		if (ret < 0) {
 			__free_page(spd.pages[i]);
 			break;
 		}
 		spd.partial[i].offset = 0;
-		spd.partial[i].len = iter->seq.len;
+		spd.partial[i].len = iter->seq.seq.len;
 
 		trace_seq_init(&iter->seq);
 	}

@@ -5673,7 +5676,7 @@ tracing_stats_read(struct file *filp, char __user *ubuf,
 	cnt = ring_buffer_read_events_cpu(trace_buf->buffer, cpu);
 	trace_seq_printf(s, "read events: %ld\n", cnt);
 
-	count = simple_read_from_buffer(ubuf, count, ppos, s->buffer, s->len);
+	count = simple_read_from_buffer(ubuf, count, ppos, s->buffer, s->seq.len);
 
 	kfree(s);
 

@@ -6636,11 +6639,11 @@ void
 trace_printk_seq(struct trace_seq *s)
 {
 	/* Probably should print a warning here. */
-	if (s->len >= TRACE_MAX_PRINT)
-		s->len = TRACE_MAX_PRINT;
+	if (s->seq.len >= TRACE_MAX_PRINT)
+		s->seq.len = TRACE_MAX_PRINT;
 
 	/* should be zero ended, but we are paranoid. */
-	s->buffer[s->len] = 0;
+	s->buffer[s->seq.len] = 0;
 
 	printk(KERN_TRACE "%s", s->buffer);
 

index f9d0cbe014b7..4d0067dd7f88 100644
@@ -1044,7 +1044,7 @@ event_filter_read(struct file *filp, char __user *ubuf, size_t cnt,
 	mutex_unlock(&event_mutex);
 
 	if (file)
-		r = simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, s->len);
+		r = simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, s->seq.len);
 
 	kfree(s);
 

@@ -1210,7 +1210,7 @@ subsystem_filter_read(struct file *filp, char __user *ubuf, size_t cnt,
 	trace_seq_init(s);
 
 	print_subsystem_event_filter(system, s);
-	r = simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, s->len);
+	r = simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, s->seq.len);
 
 	kfree(s);
 

@@ -1265,7 +1265,7 @@ show_header(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
 	trace_seq_init(s);
 
 	func(s);
-	r = simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, s->len);
+	r = simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, s->seq.len);
 
 	kfree(s);
 

index 100288d10e1f..6d1342ae7a44 100644
@@ -1154,9 +1154,9 @@ print_graph_comment(struct trace_seq *s, struct trace_entry *ent,
 	}
 
 	/* Strip ending newline */
-	if (s->buffer[s->len - 1] == '\n') {
-		s->buffer[s->len - 1] = '\0';
-		s->len--;
+	if (s->buffer[s->seq.len - 1] == '\n') {
+		s->buffer[s->seq.len - 1] = '\0';
+		s->seq.len--;
 	}
 
 	trace_seq_puts(s, " */\n");

314 lines not on this page · raw message

index 4f7a96a9d71a..38770688a627 100644
@@ -73,7 +73,7 @@ extern int seq_buf_putc(struct seq_buf *s, unsigned char c);
 extern int seq_buf_putmem(struct seq_buf *s, const void *mem, unsigned int len);
 extern int seq_buf_putmem_hex(struct seq_buf *s, const void *mem,
 			      unsigned int len);
-extern int seq_buf_path(struct seq_buf *s, const struct path *path);
+extern int seq_buf_path(struct seq_buf *s, const struct path *path, const char *esc);
 
 extern int seq_buf_bitmask(struct seq_buf *s, const unsigned long *maskp,
 			   int nmaskbits);

index e9a7861595d2..7dac34d1235b 100644
@@ -272,28 +272,32 @@ int seq_buf_putmem_hex(struct seq_buf *s, const void *mem,
  * seq_buf_path - copy a path into the sequence buffer
  * @s: seq_buf descriptor
  * @path: path to write into the sequence buffer.
+ * @esc: set of characters to escape in the output
  *
  * Write a path name into the sequence buffer.
  *
- * Returns zero on success, -1 on overflow
+ * Returns the number of written bytes on success, -1 on overflow
  */
-int seq_buf_path(struct seq_buf *s, const struct path *path)
+int seq_buf_path(struct seq_buf *s, const struct path *path, const char *esc)
 {
-	unsigned int len = seq_buf_buffer_left(s);
-	unsigned char *p;
+	char *buf = s->buffer + s->len;
+	size_t size = seq_buf_buffer_left(s);
+	int res = -1;
 
 	WARN_ON(s->size == 0);
 
-	p = d_path(path, s->buffer + s->len, len);
-	if (!IS_ERR(p)) {
-		p = mangle_path(s->buffer + s->len, p, "\n");
-		if (p) {
-			s->len = p - s->buffer;
-			return 0;
+	if (size) {
+		char *p = d_path(path, buf, size);
+		if (!IS_ERR(p)) {
+			char *end = mangle_path(buf, p, esc);
+			if (end)
+				res = end - buf;
 		}
 	}
-	seq_buf_set_overflow(s);
-	return -1;
+	if (res > 0)
+		s->len += res;
+
+	return res;
 }
 
 /**

index 8c0c54fe674b..74cacc930c24 100644
@@ -326,7 +326,6 @@ EXPORT_SYMBOL_GPL(trace_seq_putmem_hex);
 int trace_seq_path(struct trace_seq *s, const struct path *path)
 {
 	unsigned int save_len = s->seq.len;
-	int ret;
 
 	if (s->full)
 		return 0;

@@ -338,7 +337,7 @@ int trace_seq_path(struct trace_seq *s, const struct path *path)
 		return 0;
 	}
 
-	ret = seq_buf_path(&s->seq, path);
+	seq_buf_path(&s->seq, path, "\n");
 
 	if (unlikely(seq_buf_has_overflowed(&s->seq))) {
 		s->seq.len = save_len;

@@ -346,7 +345,7 @@ int trace_seq_path(struct trace_seq *s, const struct path *path)
 		return 0;
 	}
 
-	return ret;
+	return 1;
 }
 EXPORT_SYMBOL_GPL(trace_seq_path);
 

index 38770688a627..d14dc9023dde 100644
@@ -16,10 +16,10 @@
  * @readpos:	The next position to read in the buffer.
  */
 struct seq_buf {
-	unsigned char		*buffer;
-	unsigned int		size;
-	unsigned int		len;
-	unsigned int		readpos;
+	char			*buffer;
+	size_t			size;
+	size_t			len;
+	loff_t			readpos;
 };
 
 static inline void

index d14dc9023dde..5d91262433e2 100644
@@ -22,13 +22,18 @@ struct seq_buf {
 	loff_t			readpos;
 };
 
+static inline void seq_buf_clear(struct seq_buf *s)
+{
+	s->len = 0;
+	s->readpos = 0;
+}
+
 static inline void
 seq_buf_init(struct seq_buf *s, unsigned char *buf, unsigned int size)
 {
 	s->buffer = buf;
 	s->size = size;
-	s->len = 0;
-	s->readpos = 0;
+	seq_buf_clear(s);
 }
 
 /*

index 5d91262433e2..93718e570d4c 100644
@@ -64,6 +64,12 @@ seq_buf_buffer_left(struct seq_buf *s)
 	return (s->size - 1) - s->len;
 }
 
+/* How much buffer was written? */
+static inline unsigned int seq_buf_used(struct seq_buf *s)
+{
+	return min(s->len, s->size);
+}
+
 extern __printf(2, 3)
 int seq_buf_printf(struct seq_buf *s, const char *fmt, ...);
 extern __printf(2, 0)

index 7dac34d1235b..9ec5305d9da7 100644
@@ -16,9 +16,6 @@
 #include <linux/seq_file.h>
 #include <linux/seq_buf.h>
 
-/* How much buffer is written? */
-#define SEQ_BUF_USED(s) min((s)->len, (s)->size - 1)
-
 /**
  * seq_buf_print_seq - move the contents of seq_buf into a seq_file
  * @m: the seq_file descriptor that is the destination

@@ -28,7 +25,7 @@
  */
 int seq_buf_print_seq(struct seq_file *m, struct seq_buf *s)
 {
-	unsigned int len = SEQ_BUF_USED(s);
+	unsigned int len = seq_buf_used(s);
 
 	return seq_write(m, s->buffer, len);
 }

index 7d7a07e9b9e9..0aa75be843a0 100644
@@ -4575,20 +4575,33 @@ static size_t
 tracing_fill_pipe_page(size_t rem, struct trace_iterator *iter)
 {
 	size_t count;
+	int save_len;
 	int ret;
 
 	/* Seq buffer is page-sized, exactly what we need. */
 	for (;;) {
-		count = iter->seq.seq.len;
+		save_len = iter->seq.seq.len;
 		ret = print_trace_line(iter);
-		count = iter->seq.seq.len - count;
-		if (rem < count) {
-			rem = 0;
-			iter->seq.seq.len -= count;
+
+		if (trace_seq_has_overflowed(&iter->seq)) {
+			iter->seq.seq.len = save_len;
 			break;
 		}
+
+		/*
+		 * This should not be hit, because it should only
+		 * be set if the iter->seq overflowed. But check it
+		 * anyway to be safe.
+		 */
 		if (ret == TRACE_TYPE_PARTIAL_LINE) {
-			iter->seq.seq.len -= count;
+			iter->seq.seq.len = save_len;
+			break;
+		}
+
+		count = iter->seq.seq.len - save_len;
+		if (rem < count) {
+			rem = 0;
+			iter->seq.seq.len = save_len;
 			break;
 		}
 

index 85d37106be3d..cfaf5a1d4bad 100644
@@ -24,6 +24,24 @@ trace_seq_init(struct trace_seq *s)
 }
 
 /**
+ * trace_seq_used - amount of actual data written to buffer
+ * @s: trace sequence descriptor
+ *
+ * Returns the amount of data written to the buffer.
+ *
+ * IMPORTANT!
+ *
+ * Use this instead of @s->seq.len if you need to pass the amount
+ * of data from the buffer to another buffer (userspace, or what not).
+ * The @s->seq.len on overflow is bigger than the buffer size and
+ * using it can cause access to undefined memory.
+ */
+static inline int trace_seq_used(struct trace_seq *s)
+{
+	return seq_buf_used(&s->seq);
+}
+
+/**
  * trace_seq_buffer_ptr - return pointer to next location in buffer
  * @s: trace sequence descriptor
  *

@@ -35,7 +53,7 @@ trace_seq_init(struct trace_seq *s)
 static inline unsigned char *
 trace_seq_buffer_ptr(struct trace_seq *s)
 {
-	return s->buffer + s->seq.len;
+	return s->buffer + seq_buf_used(&s->seq);
 }
 
 /**

index 9ec5305d9da7..ce17f65268ed 100644
@@ -328,7 +328,7 @@ int seq_buf_to_user(struct seq_buf *s, char __user *ubuf, int cnt)
 	if (s->len <= s->readpos)
 		return -EBUSY;
 
-	len = s->len - s->readpos;
+	len = seq_buf_used(s) - s->readpos;
 	if (cnt > len)
 		cnt = len;
 	ret = copy_to_user(ubuf, s->buffer + s->readpos, cnt);

index 0aa75be843a0..9023446b2c2b 100644
@@ -944,10 +944,10 @@ static ssize_t trace_seq_to_buffer(struct trace_seq *s, void *buf, size_t cnt)
 {
 	int len;
 
-	if (s->seq.len <= s->seq.readpos)
+	if (trace_seq_used(s) <= s->seq.readpos)
 		return -EBUSY;
 
-	len = s->seq.len - s->seq.readpos;
+	len = trace_seq_used(s) - s->seq.readpos;
 	if (cnt > len)
 		cnt = len;
 	memcpy(buf, s->buffer + s->seq.readpos, cnt);

@@ -4514,18 +4514,18 @@ waitagain:
 	trace_access_lock(iter->cpu_file);
 	while (trace_find_next_entry_inc(iter) != NULL) {
 		enum print_line_t ret;
-		int len = iter->seq.seq.len;
+		int save_len = iter->seq.seq.len;
 
 		ret = print_trace_line(iter);
 		if (ret == TRACE_TYPE_PARTIAL_LINE) {
 			/* don't print partial lines */
-			iter->seq.seq.len = len;
+			iter->seq.seq.len = save_len;
 			break;
 		}
 		if (ret != TRACE_TYPE_NO_CONSUME)
 			trace_consume(iter);
 
-		if (iter->seq.seq.len >= cnt)
+		if (trace_seq_used(&iter->seq) >= cnt)
 			break;
 
 		/*

@@ -4541,7 +4541,7 @@ waitagain:
 
 	/* Now copy what we have to the user */
 	sret = trace_seq_to_user(&iter->seq, ubuf, cnt);
-	if (iter->seq.seq.readpos >= iter->seq.seq.len)
+	if (iter->seq.seq.readpos >= trace_seq_used(&iter->seq))
 		trace_seq_init(&iter->seq);
 
 	/*

@@ -4598,7 +4598,7 @@ tracing_fill_pipe_page(size_t rem, struct trace_iterator *iter)
 			break;
 		}
 
-		count = iter->seq.seq.len - save_len;
+		count = trace_seq_used(&iter->seq) - save_len;
 		if (rem < count) {
 			rem = 0;
 			iter->seq.seq.len = save_len;

@@ -4682,13 +4682,13 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
 		/* Copy the data into the page, so we can start over. */
 		ret = trace_seq_to_buffer(&iter->seq,
 					  page_address(spd.pages[i]),
-					  iter->seq.seq.len);
+					  trace_seq_used(&iter->seq));
 		if (ret < 0) {
 			__free_page(spd.pages[i]);
 			break;
 		}
 		spd.partial[i].offset = 0;
-		spd.partial[i].len = iter->seq.seq.len;
+		spd.partial[i].len = trace_seq_used(&iter->seq);
 
 		trace_seq_init(&iter->seq);
 	}

@@ -5689,7 +5689,8 @@ tracing_stats_read(struct file *filp, char __user *ubuf,
 	cnt = ring_buffer_read_events_cpu(trace_buf->buffer, cpu);
 	trace_seq_printf(s, "read events: %ld\n", cnt);
 
-	count = simple_read_from_buffer(ubuf, count, ppos, s->buffer, s->seq.len);
+	count = simple_read_from_buffer(ubuf, count, ppos,
+					s->buffer, trace_seq_used(s));
 
 	kfree(s);
 

index 4d0067dd7f88..935cbea78532 100644
@@ -1044,7 +1044,8 @@ event_filter_read(struct file *filp, char __user *ubuf, size_t cnt,
 	mutex_unlock(&event_mutex);
 
 	if (file)
-		r = simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, s->seq.len);
+		r = simple_read_from_buffer(ubuf, cnt, ppos,
+					    s->buffer, trace_seq_used(s));
 
 	kfree(s);
 

@@ -1210,7 +1211,8 @@ subsystem_filter_read(struct file *filp, char __user *ubuf, size_t cnt,
 	trace_seq_init(s);
 
 	print_subsystem_event_filter(system, s);
-	r = simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, s->seq.len);
+	r = simple_read_from_buffer(ubuf, cnt, ppos,
+				    s->buffer, trace_seq_used(s));
 
 	kfree(s);
 

@@ -1265,7 +1267,8 @@ show_header(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
 	trace_seq_init(s);
 
 	func(s);
-	r = simple_read_from_buffer(ubuf, cnt, ppos, s->buffer, s->seq.len);
+	r = simple_read_from_buffer(ubuf, cnt, ppos,
+				    s->buffer, trace_seq_used(s));
 
 	kfree(s);
 

index 6d1342ae7a44..ec35468349a7 100644
@@ -1153,6 +1153,9 @@ print_graph_comment(struct trace_seq *s, struct trace_entry *ent,
 			return ret;
 	}
 
+	if (trace_seq_has_overflowed(s))
+		goto out;
+
 	/* Strip ending newline */
 	if (s->buffer[s->seq.len - 1] == '\n') {
 		s->buffer[s->seq.len - 1] = '\0';

@@ -1160,7 +1163,7 @@ print_graph_comment(struct trace_seq *s, struct trace_entry *ent,
 	}
 
 	trace_seq_puts(s, " */\n");
-
+ out:
 	return trace_handle_return(s);
 }
 

index 74cacc930c24..f8b45d8792f9 100644
@@ -30,7 +30,7 @@
 #define TRACE_SEQ_BUF_LEFT(s) seq_buf_buffer_left(&(s)->seq)
 
 /* How much buffer is written? */
-#define TRACE_SEQ_BUF_USED(s) min((s)->seq.len, (unsigned int)(PAGE_SIZE - 1))
+#define TRACE_SEQ_BUF_USED(s) seq_buf_used(&(s)->seq)
 
 /*
  * trace_seq should work with being initialized with 0s.

index 9023446b2c2b..26facec4625e 100644
@@ -6656,6 +6656,14 @@ trace_printk_seq(struct trace_seq *s)
 	if (s->seq.len >= TRACE_MAX_PRINT)
 		s->seq.len = TRACE_MAX_PRINT;
 
+	/*
+	 * More paranoid code. Although the buffer size is set to
+	 * PAGE_SIZE, and TRACE_MAX_PRINT is 1000, this is just
+	 * an extra layer of protection.
+	 */
+	if (WARN_ON_ONCE(s->seq.len >= s->seq.size))
+		s->seq.len = s->seq.size - 1;
+
 	/* should be zero ended, but we are paranoid. */
 	s->buffer[s->seq.len] = 0;
 

index ce17f65268ed..6fc9d021cbef 100644
@@ -17,6 +17,19 @@
 #include <linux/seq_buf.h>
 
 /**
+ * seq_buf_can_fit - can the new data fit in the current buffer?
+ * @s: the seq_buf descriptor
+ * @len: The length to see if it can fit in the current buffer
+ *
+ * Returns true if there's enough unused space in the seq_buf buffer
+ * to fit the amount of new data according to @len.
+ */
+static bool seq_buf_can_fit(struct seq_buf *s, size_t len)
+{
+	return s->len + len < s->size;
+}
+
+/**
  * seq_buf_print_seq - move the contents of seq_buf into a seq_file
  * @m: the seq_file descriptor that is the destination
  * @s: the seq_buf descriptor that is the source.

@@ -48,7 +61,7 @@ int seq_buf_vprintf(struct seq_buf *s, const char *fmt, va_list args)
 
 	if (s->len < s->size) {
 		len = vsnprintf(s->buffer + s->len, s->size - s->len, fmt, args);
-		if (s->len + len < s->size) {
+		if (seq_buf_can_fit(s, len)) {
 			s->len += len;
 			return 0;
 		}

@@ -137,7 +150,7 @@ int seq_buf_bprintf(struct seq_buf *s, const char *fmt, const u32 *binary)
 
 	if (s->len < s->size) {
 		ret = bstr_printf(s->buffer + s->len, len, fmt, binary);
-		if (s->len + ret < s->size) {
+		if (seq_buf_can_fit(s, ret)) {
 			s->len += ret;
 			return 0;
 		}

@@ -161,7 +174,7 @@ int seq_buf_puts(struct seq_buf *s, const char *str)
 
 	WARN_ON(s->size == 0);
 
-	if (s->len + len < s->size) {
+	if (seq_buf_can_fit(s, len)) {
 		memcpy(s->buffer + s->len, str, len);
 		s->len += len;
 		return 0;

@@ -183,7 +196,7 @@ int seq_buf_putc(struct seq_buf *s, unsigned char c)
 {
 	WARN_ON(s->size == 0);
 
-	if (s->len + 1 < s->size) {
+	if (seq_buf_can_fit(s, 1)) {
 		s->buffer[s->len++] = c;
 		return 0;
 	}

@@ -207,7 +220,7 @@ int seq_buf_putmem(struct seq_buf *s, const void *mem, unsigned int len)
 {
 	WARN_ON(s->size == 0);
 
-	if (s->len + len < s->size) {
+	if (seq_buf_can_fit(s, len)) {
 		memcpy(s->buffer + s->len, mem, len);
 		s->len += len;
 		return 0;

index 93718e570d4c..0800a24b4348 100644
@@ -43,13 +43,13 @@ seq_buf_init(struct seq_buf *s, unsigned char *buf, unsigned int size)
 static inline bool
 seq_buf_has_overflowed(struct seq_buf *s)
 {
-	return s->len == s->size;
+	return s->len > s->size;
 }
 
 static inline void
 seq_buf_set_overflow(struct seq_buf *s)
 {
-	s->len = s->size;
+	s->len = s->size + 1;
 }
 
 /*

@@ -61,7 +61,7 @@ seq_buf_buffer_left(struct seq_buf *s)
 	if (seq_buf_has_overflowed(s))
 		return 0;
 
-	return (s->size - 1) - s->len;
+	return s->size - s->len;
 }
 
 /* How much buffer was written? */

index 6fc9d021cbef..c53f1d5088e8 100644
@@ -26,7 +26,7 @@
  */
 static bool seq_buf_can_fit(struct seq_buf *s, size_t len)
 {
-	return s->len + len < s->size;
+	return s->len + len <= s->size;
 }
 
 /**

@@ -110,8 +110,11 @@ int seq_buf_bitmask(struct seq_buf *s, const unsigned long *maskp,
 	WARN_ON(s->size == 0);
 
 	/*
-	 * The last byte of the buffer is used to determine if we
-	 * overflowed or not.
+	 * Note, because bitmap_scnprintf() only returns the number of bytes
+	 * written and not the number that would be written, we use the last
+	 * byte of the buffer to let us know if we overflowed. There's a small
+	 * chance that the bitmap could have fit exactly inside the buffer, but
+	 * it's not that critical if that does happen.
 	 */
 	if (len > 1) {
 		ret = bitmap_scnprintf(s->buffer + s->len, len, maskp, nmaskbits);

index 0800a24b4348..12c64282aa98 100644
@@ -70,6 +70,47 @@ static inline unsigned int seq_buf_used(struct seq_buf *s)
 	return min(s->len, s->size);
 }
 
+/**
+ * seq_buf_get_buf - get buffer to write arbitrary data to
+ * @s: the seq_buf handle
+ * @bufp: the beginning of the buffer is stored here
+ *
+ * Return the number of bytes available in the buffer, or zero if
+ * there's no space.
+ */
+static inline size_t seq_buf_get_buf(struct seq_buf *s, char **bufp)
+{
+	WARN_ON(s->len > s->size + 1);
+
+	if (s->len < s->size) {
+		*bufp = s->buffer + s->len;
+		return s->size - s->len;
+	}
+
+	*bufp = NULL;
+	return 0;
+}
+
+/**
+ * seq_buf_commit - commit data to the buffer
+ * @s: the seq_buf handle
+ * @num: the number of bytes to commit
+ *
+ * Commit @num bytes of data written to a buffer previously acquired
+ * by seq_buf_get.  To signal an error condition, or that the data
+ * didn't fit in the available space, pass a negative @num value.
+ */
+static inline void seq_buf_commit(struct seq_buf *s, int num)
+{
+	if (num < 0) {
+		seq_buf_set_overflow(s);
+	} else {
+		/* num must be negative on overflow */
+		BUG_ON(s->len + num > s->size);
+		s->len += num;
+	}
+}
+
 extern __printf(2, 3)
 int seq_buf_printf(struct seq_buf *s, const char *fmt, ...);
 extern __printf(2, 0)

index c53f1d5088e8..086f594ac890 100644
@@ -293,8 +293,8 @@ int seq_buf_putmem_hex(struct seq_buf *s, const void *mem,
  */
 int seq_buf_path(struct seq_buf *s, const struct path *path, const char *esc)
 {
-	char *buf = s->buffer + s->len;
-	size_t size = seq_buf_buffer_left(s);
+	char *buf;
+	size_t size = seq_buf_get_buf(s, &buf);
 	int res = -1;
 
 	WARN_ON(s->size == 0);

@@ -307,8 +307,7 @@ int seq_buf_path(struct seq_buf *s, const struct path *path, const char *esc)
 				res = end - buf;
 		}
 	}
-	if (res > 0)
-		s->len += res;
+	seq_buf_commit(s, res);
 
 	return res;
 }

index 12c64282aa98..9aafe0e24c68 100644
@@ -115,8 +115,6 @@ extern __printf(2, 3)
 int seq_buf_printf(struct seq_buf *s, const char *fmt, ...);
 extern __printf(2, 0)
 int seq_buf_vprintf(struct seq_buf *s, const char *fmt, va_list args);
-extern int
-seq_buf_bprintf(struct seq_buf *s, const char *fmt, const u32 *binary);
 extern int seq_buf_print_seq(struct seq_file *m, struct seq_buf *s);
 extern int seq_buf_to_user(struct seq_buf *s, char __user *ubuf,
 			   int cnt);

@@ -130,4 +128,9 @@ extern int seq_buf_path(struct seq_buf *s, const struct path *path, const char *
 extern int seq_buf_bitmask(struct seq_buf *s, const unsigned long *maskp,
 			   int nmaskbits);
 
+#ifdef CONFIG_BINARY_PRINTF
+extern int
+seq_buf_bprintf(struct seq_buf *s, const char *fmt, const u32 *binary);
+#endif
+
 #endif /* _LINUX_SEQ_BUF_H */

index 086f594ac890..4eedfedb9e31 100644
@@ -127,6 +127,7 @@ int seq_buf_bitmask(struct seq_buf *s, const unsigned long *maskp,
 	return -1;
 }
 
+#ifdef CONFIG_BINARY_PRINTF
 /**
  * seq_buf_bprintf - Write the printf string from binary arguments
  * @s: seq_buf descriptor

@@ -161,6 +162,7 @@ int seq_buf_bprintf(struct seq_buf *s, const char *fmt, const u32 *binary)
 	seq_buf_set_overflow(s);
 	return -1;
 }
+#endif /* CONFIG_BINARY_PRINTF */
 
 /**
  * seq_buf_puts - sequence printing of simple string

359 lines not on this page · raw message

359 lines not on this page · raw message

index a3aa63e47637..ba2e85a0ff5b 100644
@@ -134,4 +134,7 @@ extern phys_addr_t per_cpu_ptr_to_phys(void *addr);
 	(typeof(type) __percpu *)__alloc_percpu(sizeof(type),		\
 						__alignof__(type))
 
+/* To avoid include hell, as printk can not declare this, we declare it here */
+DECLARE_PER_CPU(printk_func_t, printk_func);
+
 #endif /* __LINUX_PERCPU_H */

index d78125f73ac4..3bbd979d32fb 100644
@@ -162,6 +162,8 @@ extern int kptr_restrict;
 
 extern void wake_up_klogd(void);
 
+typedef int(*printk_func_t)(const char *fmt, va_list args);
+
 void log_buf_kexec_setup(void);
 void __init setup_log_buf(int early);
 void dump_stack_set_arch_desc(const char *fmt, ...);

index ced2b84b1cb7..f7b723f98cb9 100644
@@ -1807,6 +1807,30 @@ asmlinkage int printk_emit(int facility, int level,
 }
 EXPORT_SYMBOL(printk_emit);
 
+int vprintk_default(const char *fmt, va_list args)
+{
+	int r;
+
+#ifdef CONFIG_KGDB_KDB
+	if (unlikely(kdb_trap_printk)) {
+		r = vkdb_printf(fmt, args);
+		return r;
+	}
+#endif
+	r = vprintk_emit(0, -1, NULL, 0, fmt, args);
+
+	return r;
+}
+EXPORT_SYMBOL_GPL(vprintk_default);
+
+/*
+ * This allows printk to be diverted to another function per cpu.
+ * This is useful for calling printk functions from within NMI
+ * without worrying about race conditions that can lock up the
+ * box.
+ */
+DEFINE_PER_CPU(printk_func_t, printk_func) = vprintk_default;
+
 /**
  * printk - print a kernel message
  * @fmt: format string

@@ -1830,19 +1854,15 @@ EXPORT_SYMBOL(printk_emit);
  */
 asmlinkage __visible int printk(const char *fmt, ...)
 {
+	printk_func_t vprintk_func;
 	va_list args;
 	int r;
 
-#ifdef CONFIG_KGDB_KDB
-	if (unlikely(kdb_trap_printk)) {
-		va_start(args, fmt);
-		r = vkdb_printf(fmt, args);
-		va_end(args);
-		return r;
-	}
-#endif
 	va_start(args, fmt);
-	r = vprintk_emit(0, -1, NULL, 0, fmt, args);
+	preempt_disable();
+	vprintk_func = this_cpu_read(printk_func);
+	r = vprintk_func(fmt, args);
+	preempt_enable();
 	va_end(args);
 
 	return r;

index 6a1e71bde323..c95c3e9ce196 100644
@@ -18,6 +18,7 @@
 #include <linux/nmi.h>
 #include <linux/module.h>
 #include <linux/delay.h>
+#include <linux/seq_buf.h>
 
 #ifdef CONFIG_HARDLOCKUP_DETECTOR
 u64 hw_nmi_get_sample_period(int watchdog_thresh)

@@ -29,14 +30,35 @@ u64 hw_nmi_get_sample_period(int watchdog_thresh)
 #ifdef arch_trigger_all_cpu_backtrace
 /* For reliability, we're prepared to waste bits here. */
 static DECLARE_BITMAP(backtrace_mask, NR_CPUS) __read_mostly;
+static cpumask_var_t printtrace_mask;
+
+#define NMI_BUF_SIZE		4096
+
+struct nmi_seq_buf {
+	unsigned char		buffer[NMI_BUF_SIZE];
+	struct seq_buf		seq;
+};
+
+/* Safe printing in NMI context */
+static DEFINE_PER_CPU(struct nmi_seq_buf, nmi_print_seq);
 
 /* "in progress" flag of arch_trigger_all_cpu_backtrace */
 static unsigned long backtrace_flag;
 
+static void print_seq_line(struct nmi_seq_buf *s, int start, int end)
+{
+	const char *buf = s->buffer + start;
+
+	printk("%.*s", (end - start) + 1, buf);
+}
+
 void arch_trigger_all_cpu_backtrace(bool include_self)
 {
+	struct nmi_seq_buf *s;
+	int len;
+	int cpu;
 	int i;
-	int cpu = get_cpu();
+	int this_cpu = get_cpu();
 
 	if (test_and_set_bit(0, &backtrace_flag)) {
 		/*

@@ -49,7 +71,17 @@ void arch_trigger_all_cpu_backtrace(bool include_self)
 
 	cpumask_copy(to_cpumask(backtrace_mask), cpu_online_mask);
 	if (!include_self)
-		cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
+		cpumask_clear_cpu(this_cpu, to_cpumask(backtrace_mask));
+
+	cpumask_copy(printtrace_mask, to_cpumask(backtrace_mask));
+	/*
+	 * Set up per_cpu seq_buf buffers that the NMIs running on the other
+	 * CPUs will write to.
+	 */
+	for_each_cpu(cpu, to_cpumask(backtrace_mask)) {
+		s = &per_cpu(nmi_print_seq, cpu);
+		seq_buf_init(&s->seq, s->buffer, NMI_BUF_SIZE);
+	}
 
 	if (!cpumask_empty(to_cpumask(backtrace_mask))) {
 		pr_info("sending NMI to %s CPUs:\n",

@@ -65,11 +97,58 @@ void arch_trigger_all_cpu_backtrace(bool include_self)
 		touch_softlockup_watchdog();
 	}
 
+	/*
+	 * Now that all the NMIs have triggered, we can dump out their
+	 * back traces safely to the console.
+	 */
+	for_each_cpu(cpu, printtrace_mask) {
+		int last_i = 0;
+
+		s = &per_cpu(nmi_print_seq, cpu);
+		len = seq_buf_used(&s->seq);
+		if (!len)
+			continue;
+
+		/* Print line by line. */
+		for (i = 0; i < len; i++) {
+			if (s->buffer[i] == '\n') {
+				print_seq_line(s, last_i, i);
+				last_i = i + 1;
+			}
+		}
+		/* Check if there was a partial line. */
+		if (last_i < len) {
+			print_seq_line(s, last_i, len - 1);
+			pr_cont("\n");
+		}
+	}
+
 	clear_bit(0, &backtrace_flag);
 	smp_mb__after_atomic();
 	put_cpu();
 }
 
+/*
+ * It is not safe to call printk() directly from NMI handlers.
+ * It may be fine if the NMI detected a lock up and we have no choice
+ * but to do so, but doing a NMI on all other CPUs to get a back trace
+ * can be done with a sysrq-l. We don't want that to lock up, which
+ * can happen if the NMI interrupts a printk in progress.
+ *
+ * Instead, we redirect the vprintk() to this nmi_vprintk() that writes
+ * the content into a per cpu seq_buf buffer. Then when the NMIs are
+ * all done, we can safely dump the contents of the seq_buf to a printk()
+ * from a non NMI context.
+ */
+static int nmi_vprintk(const char *fmt, va_list args)
+{
+	struct nmi_seq_buf *s = this_cpu_ptr(&nmi_print_seq);
+	unsigned int len = seq_buf_used(&s->seq);
+
+	seq_buf_vprintf(&s->seq, fmt, args);
+	return seq_buf_used(&s->seq) - len;
+}
+
 static int
 arch_trigger_all_cpu_backtrace_handler(unsigned int cmd, struct pt_regs *regs)
 {

@@ -78,12 +157,14 @@ arch_trigger_all_cpu_backtrace_handler(unsigned int cmd, struct pt_regs *regs)
 	cpu = smp_processor_id();
 
 	if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
-		static arch_spinlock_t lock = __ARCH_SPIN_LOCK_UNLOCKED;
+		printk_func_t printk_func_save = this_cpu_read(printk_func);
 
-		arch_spin_lock(&lock);
+		/* Replace printk to write into the NMI seq */
+		this_cpu_write(printk_func, nmi_vprintk);
 		printk(KERN_WARNING "NMI backtrace for cpu %d\n", cpu);
 		show_regs(regs);
-		arch_spin_unlock(&lock);
+		this_cpu_write(printk_func, printk_func_save);
+
 		cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
 		return NMI_HANDLED;
 	}