Merge tag 'trace-seq-buf-3.19' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull nmi-safe seq_buf printk update from Steven Rostedt:
 "This code is a fork from the trace-3.19 pull as it needed the
  trace_seq clean ups from that branch.

  This code solves the issue of performing stack dumps from NMI context.
  The issue is that printk() is not safe from NMI context as if the NMI
  were to trigger when a printk() was being performed, the NMI could
  deadlock from the printk() internal locks.  This has been seen in
  practice.

  With lots of review from Petr Mladek, this code went through several
  iterations, and we feel that it is now at a point of quality to be
  accepted into mainline.

  Here's what is contained in this patch set:

   - Creates a "seq_buf" generic buffer utility that allows a descriptor
     to be passed around where functions can write their own "printk()"
     formatted strings into it.  The generic version was pulled out of
     the trace_seq() code that was made specifically for tracing.

   - The seq_buf code was change to model the seq_file code.  I have a
     patch (not included for 3.19) that converts the seq_file.c code
     over to use seq_buf.c like the trace_seq.c code does.  This was
     done to make sure that seq_buf.c is compatible with seq_file.c.  I
     may try to get that patch in for 3.20.

   - The seq_buf.c file was moved to lib/ to remove it from being
     dependent on CONFIG_TRACING.

   - The printk() was updated to allow for a per_cpu "override" of the
     internal calls.  That is, instead of writing to the console, a call
     to printk() may do something else.  This made it easier to allow
     the NMI to change what printk() does in order to call dump_stack()
     without needing to update that code as well.

   - Finally, the dump_stack from all CPUs via NMI code was converted to
     use the seq_buf code.  The caller to trigger the NMI code would
     wait till all the NMIs finished, and then it would print the
     seq_buf data to the console safely from a non NMI context

  One added bonus is that this code also makes the NMI dump stack work
  on PREEMPT_RT kernels.  As printk() includes sleeping locks on
  PREEMPT_RT, printk() only writes to console if the console does not
  use any rt_mutex converted spin locks.  Which a lot do"

* tag 'trace-seq-buf-3.19' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  x86/nmi: Fix use of unallocated cpumask_var_t
  printk/percpu: Define printk_func when printk is not defined
  x86/nmi: Perform a safe NMI stack trace on all CPUs
  printk: Add per_cpu printk func to allow printk to be diverted
  seq_buf: Move the seq_buf code to lib/
  seq-buf: Make seq_buf_bprintf() conditional on CONFIG_BINARY_PRINTF
  tracing: Add seq_buf_get_buf() and seq_buf_commit() helper functions
  tracing: Have seq_buf use full buffer
  seq_buf: Add seq_buf_can_fit() helper function
  tracing: Add paranoid size check in trace_printk_seq()
  tracing: Use trace_seq_used() and seq_buf_used() instead of len
  tracing: Clean up tracing_fill_pipe_page()
  seq_buf: Create seq_buf_used() to find out how much was written
  tracing: Add a seq_buf_clear() helper and clear len and readpos in init
  tracing: Convert seq_buf fields to be like seq_file fields
  tracing: Convert seq_buf_path() to be like seq_path()
  tracing: Create seq_buf layer in trace_seq

1 files changed, 82 insertions, 95 deletions

diff --git a/kernel/trace/trace_seq.c b/kernel/trace/trace_seq.c
index fabfa0f190a3..f8b45d8792f9 100644
--- a/kernel/trace/trace_seq.c
+++ b/kernel/trace/trace_seq.c
@@ -27,10 +27,19 @@
 #include <linux/trace_seq.h>
 
 /* How much buffer is left on the trace_seq? */
-#define TRACE_SEQ_BUF_LEFT(s) ((PAGE_SIZE - 1) - (s)->len)
+#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)->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.
+ */
+static inline void __trace_seq_init(struct trace_seq *s)
+{
+	if (unlikely(!s->seq.size))
+		trace_seq_init(s);
+}
 
 /**
  * trace_print_seq - move the contents of trace_seq into a seq_file
@@ -43,10 +52,11 @@
  */
 int trace_print_seq(struct seq_file *m, struct trace_seq *s)
 {
-	unsigned int len = TRACE_SEQ_BUF_USED(s);
 	int ret;
 
-	ret = seq_write(m, s->buffer, len);
+	__trace_seq_init(s);
+
+	ret = seq_buf_print_seq(m, &s->seq);
 
 	/*
 	 * Only reset this buffer if we successfully wrote to the
@@ -72,24 +82,23 @@ int trace_print_seq(struct seq_file *m, struct trace_seq *s)
  */
 void trace_seq_printf(struct trace_seq *s, const char *fmt, ...)
 {
-	unsigned int len = TRACE_SEQ_BUF_LEFT(s);
+	unsigned int save_len = s->seq.len;
 	va_list ap;
-	int ret;
 
-	if (s->full || !len)
+	if (s->full)
 		return;
 
+	__trace_seq_init(s);
+
 	va_start(ap, fmt);
-	ret = vsnprintf(s->buffer + s->len, len, fmt, ap);
+	seq_buf_vprintf(&s->seq, fmt, ap);
 	va_end(ap);
 
 	/* If we can't write it all, don't bother writing anything */
-	if (ret >= len) {
+	if (unlikely(seq_buf_has_overflowed(&s->seq))) {
+		s->seq.len = save_len;
 		s->full = 1;
-		return;
 	}
-
-	s->len += ret;
 }
 EXPORT_SYMBOL_GPL(trace_seq_printf);
 
@@ -104,14 +113,19 @@ EXPORT_SYMBOL_GPL(trace_seq_printf);
 void trace_seq_bitmask(struct trace_seq *s, const unsigned long *maskp,
 		      int nmaskbits)
 {
-	unsigned int len = TRACE_SEQ_BUF_LEFT(s);
-	int ret;
+	unsigned int save_len = s->seq.len;
 
-	if (s->full || !len)
+	if (s->full)
 		return;
 
-	ret = bitmap_scnprintf(s->buffer + s->len, len, maskp, nmaskbits);
-	s->len += ret;
+	__trace_seq_init(s);
+
+	seq_buf_bitmask(&s->seq, maskp, nmaskbits);
+
+	if (unlikely(seq_buf_has_overflowed(&s->seq))) {
+		s->seq.len = save_len;
+		s->full = 1;
+	}
 }
 EXPORT_SYMBOL_GPL(trace_seq_bitmask);
 
@@ -128,21 +142,20 @@ EXPORT_SYMBOL_GPL(trace_seq_bitmask);
  */
 void trace_seq_vprintf(struct trace_seq *s, const char *fmt, va_list args)
 {
-	unsigned int len = TRACE_SEQ_BUF_LEFT(s);
-	int ret;
+	unsigned int save_len = s->seq.len;
 
-	if (s->full || !len)
+	if (s->full)
 		return;
 
-	ret = vsnprintf(s->buffer + s->len, len, fmt, args);
+	__trace_seq_init(s);
+
+	seq_buf_vprintf(&s->seq, fmt, args);
 
 	/* If we can't write it all, don't bother writing anything */
-	if (ret >= len) {
+	if (unlikely(seq_buf_has_overflowed(&s->seq))) {
+		s->seq.len = save_len;
 		s->full = 1;
-		return;
 	}
-
-	s->len += ret;
 }
 EXPORT_SYMBOL_GPL(trace_seq_vprintf);
 
@@ -163,21 +176,21 @@ EXPORT_SYMBOL_GPL(trace_seq_vprintf);
  */
 void trace_seq_bprintf(struct trace_seq *s, const char *fmt, const u32 *binary)
 {
-	unsigned int len = TRACE_SEQ_BUF_LEFT(s);
-	int ret;
+	unsigned int save_len = s->seq.len;
 
-	if (s->full || !len)
+	if (s->full)
 		return;
 
-	ret = bstr_printf(s->buffer + s->len, len, fmt, binary);
+	__trace_seq_init(s);
+
+	seq_buf_bprintf(&s->seq, fmt, binary);
 
 	/* If we can't write it all, don't bother writing anything */
-	if (ret >= len) {
+	if (unlikely(seq_buf_has_overflowed(&s->seq))) {
+		s->seq.len = save_len;
 		s->full = 1;
 		return;
 	}
-
-	s->len += ret;
 }
 EXPORT_SYMBOL_GPL(trace_seq_bprintf);
 
@@ -198,13 +211,14 @@ void trace_seq_puts(struct trace_seq *s, const char *str)
 	if (s->full)
 		return;
 
+	__trace_seq_init(s);
+
 	if (len > TRACE_SEQ_BUF_LEFT(s)) {
 		s->full = 1;
 		return;
 	}
 
-	memcpy(s->buffer + s->len, str, len);
-	s->len += len;
+	seq_buf_putmem(&s->seq, str, len);
 }
 EXPORT_SYMBOL_GPL(trace_seq_puts);
 
@@ -223,12 +237,14 @@ void trace_seq_putc(struct trace_seq *s, unsigned char c)
 	if (s->full)
 		return;
 
+	__trace_seq_init(s);
+
 	if (TRACE_SEQ_BUF_LEFT(s) < 1) {
 		s->full = 1;
 		return;
 	}
 
-	s->buffer[s->len++] = c;
+	seq_buf_putc(&s->seq, c);
 }
 EXPORT_SYMBOL_GPL(trace_seq_putc);
 
@@ -247,19 +263,17 @@ void trace_seq_putmem(struct trace_seq *s, const void *mem, unsigned int len)
 	if (s->full)
 		return;
 
+	__trace_seq_init(s);
+
 	if (len > TRACE_SEQ_BUF_LEFT(s)) {
 		s->full = 1;
 		return;
 	}
 
-	memcpy(s->buffer + s->len, mem, len);
-	s->len += len;
+	seq_buf_putmem(&s->seq, mem, len);
 }
 EXPORT_SYMBOL_GPL(trace_seq_putmem);
 
-#define MAX_MEMHEX_BYTES	8U
-#define HEX_CHARS		(MAX_MEMHEX_BYTES*2 + 1)
-
 /**
  * trace_seq_putmem_hex - write raw memory into the buffer in ASCII hex
  * @s: trace sequence descriptor
@@ -273,32 +287,26 @@ EXPORT_SYMBOL_GPL(trace_seq_putmem);
 void trace_seq_putmem_hex(struct trace_seq *s, const void *mem,
 			 unsigned int len)
 {
-	unsigned char hex[HEX_CHARS];
-	const unsigned char *data = mem;
-	unsigned int start_len;
-	int i, j;
+	unsigned int save_len = s->seq.len;
 
 	if (s->full)
 		return;
 
-	while (len) {
-		start_len = min(len, HEX_CHARS - 1);
-#ifdef __BIG_ENDIAN
-		for (i = 0, j = 0; i < start_len; i++) {
-#else
-		for (i = start_len-1, j = 0; i >= 0; i--) {
-#endif
-			hex[j++] = hex_asc_hi(data[i]);
-			hex[j++] = hex_asc_lo(data[i]);
-		}
-		if (WARN_ON_ONCE(j == 0 || j/2 > len))
-			break;
-
-		/* j increments twice per loop */
-		len -= j / 2;
-		hex[j++] = ' ';
-
-		trace_seq_putmem(s, hex, j);
+	__trace_seq_init(s);
+
+	/* Each byte is represented by two chars */
+	if (len * 2 > TRACE_SEQ_BUF_LEFT(s)) {
+		s->full = 1;
+		return;
+	}
+
+	/* The added spaces can still cause an overflow */
+	seq_buf_putmem_hex(&s->seq, mem, len);
+
+	if (unlikely(seq_buf_has_overflowed(&s->seq))) {
+		s->seq.len = save_len;
+		s->full = 1;
+		return;
 	}
 }
 EXPORT_SYMBOL_GPL(trace_seq_putmem_hex);
@@ -317,30 +325,27 @@ EXPORT_SYMBOL_GPL(trace_seq_putmem_hex);
  */
 int trace_seq_path(struct trace_seq *s, const struct path *path)
 {
-	unsigned char *p;
+	unsigned int save_len = s->seq.len;
 
 	if (s->full)
 		return 0;
 
+	__trace_seq_init(s);
+
 	if (TRACE_SEQ_BUF_LEFT(s) < 1) {
 		s->full = 1;
 		return 0;
 	}
 
-	p = d_path(path, s->buffer + s->len, PAGE_SIZE - s->len);
-	if (!IS_ERR(p)) {
-		p = mangle_path(s->buffer + s->len, p, "\n");
-		if (p) {
-			s->len = p - s->buffer;
-			return 1;
-		}
-	} else {
-		s->buffer[s->len++] = '?';
-		return 1;
+	seq_buf_path(&s->seq, path, "\n");
+
+	if (unlikely(seq_buf_has_overflowed(&s->seq))) {
+		s->seq.len = save_len;
+		s->full = 1;
+		return 0;
 	}
 
-	s->full = 1;
-	return 0;
+	return 1;
 }
 EXPORT_SYMBOL_GPL(trace_seq_path);
 
@@ -366,25 +371,7 @@ EXPORT_SYMBOL_GPL(trace_seq_path);
  */
 int trace_seq_to_user(struct trace_seq *s, char __user *ubuf, int cnt)
 {
-	int len;
-	int ret;
-
-	if (!cnt)
-		return 0;
-
-	if (s->len <= s->readpos)
-		return -EBUSY;
-
-	len = s->len - s->readpos;
-	if (cnt > len)
-		cnt = len;
-	ret = copy_to_user(ubuf, s->buffer + s->readpos, cnt);
-	if (ret == cnt)
-		return -EFAULT;
-
-	cnt -= ret;
-
-	s->readpos += cnt;
-	return cnt;
+	__trace_seq_init(s);
+	return seq_buf_to_user(&s->seq, ubuf, cnt);
 }
 EXPORT_SYMBOL_GPL(trace_seq_to_user);