tracing: kdb: Fix ftdump to not sleep

index 5b9ae62272bb..503778920448 100644
@@ -128,7 +128,7 @@ ring_buffer_consume(struct ring_buffer *buffer, int cpu, u64 *ts,
 		    unsigned long *lost_events);
 
 struct ring_buffer_iter *
-ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu);
+ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu, gfp_t flags);
 void ring_buffer_read_prepare_sync(void);
 void ring_buffer_read_start(struct ring_buffer_iter *iter);
 void ring_buffer_read_finish(struct ring_buffer_iter *iter);

index 06e864a334bb..b49affb4666b 100644
@@ -4205,6 +4205,7 @@ EXPORT_SYMBOL_GPL(ring_buffer_consume);
  * ring_buffer_read_prepare - Prepare for a non consuming read of the buffer
  * @buffer: The ring buffer to read from
  * @cpu: The cpu buffer to iterate over
+ * @flags: gfp flags to use for memory allocation
  *
  * This performs the initial preparations necessary to iterate
  * through the buffer.  Memory is allocated, buffer recording

@@ -4222,7 +4223,7 @@ EXPORT_SYMBOL_GPL(ring_buffer_consume);
  * This overall must be paired with ring_buffer_read_finish.
  */
 struct ring_buffer_iter *
-ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu)
+ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu, gfp_t flags)
 {
 	struct ring_buffer_per_cpu *cpu_buffer;
 	struct ring_buffer_iter *iter;

@@ -4230,7 +4231,7 @@ ring_buffer_read_prepare(struct ring_buffer *buffer, int cpu)
 	if (!cpumask_test_cpu(cpu, buffer->cpumask))
 		return NULL;
 
-	iter = kmalloc(sizeof(*iter), GFP_KERNEL);
+	iter = kmalloc(sizeof(*iter), flags);
 	if (!iter)
 		return NULL;
 

index c4238b441624..8867a93246d6 100644
@@ -3904,7 +3904,8 @@ __tracing_open(struct inode *inode, struct file *file, bool snapshot)
 	if (iter->cpu_file == RING_BUFFER_ALL_CPUS) {
 		for_each_tracing_cpu(cpu) {
 			iter->buffer_iter[cpu] =
-				ring_buffer_read_prepare(iter->trace_buffer->buffer, cpu);
+				ring_buffer_read_prepare(iter->trace_buffer->buffer,
+							 cpu, GFP_KERNEL);
 		}
 		ring_buffer_read_prepare_sync();
 		for_each_tracing_cpu(cpu) {

@@ -3914,7 +3915,8 @@ __tracing_open(struct inode *inode, struct file *file, bool snapshot)
 	} else {
 		cpu = iter->cpu_file;
 		iter->buffer_iter[cpu] =
-			ring_buffer_read_prepare(iter->trace_buffer->buffer, cpu);
+			ring_buffer_read_prepare(iter->trace_buffer->buffer,
+						 cpu, GFP_KERNEL);
 		ring_buffer_read_prepare_sync();
 		ring_buffer_read_start(iter->buffer_iter[cpu]);
 		tracing_iter_reset(iter, cpu);

index d953c163a079..810d78a8d14c 100644
@@ -51,14 +51,16 @@ static void ftrace_dump_buf(int skip_lines, long cpu_file)
 	if (cpu_file == RING_BUFFER_ALL_CPUS) {
 		for_each_tracing_cpu(cpu) {
 			iter.buffer_iter[cpu] =
-			ring_buffer_read_prepare(iter.trace_buffer->buffer, cpu);
+			ring_buffer_read_prepare(iter.trace_buffer->buffer,
+						 cpu, GFP_ATOMIC);
 			ring_buffer_read_start(iter.buffer_iter[cpu]);
 			tracing_iter_reset(&iter, cpu);
 		}
 	} else {
 		iter.cpu_file = cpu_file;
 		iter.buffer_iter[cpu_file] =
-			ring_buffer_read_prepare(iter.trace_buffer->buffer, cpu_file);
+			ring_buffer_read_prepare(iter.trace_buffer->buffer,
+						 cpu_file, GFP_ATOMIC);
 		ring_buffer_read_start(iter.buffer_iter[cpu_file]);
 		tracing_iter_reset(&iter, cpu_file);
 	}

index 810d78a8d14c..7614b5c529f6 100644
@@ -17,7 +17,7 @@
 #include "trace.h"
 #include "trace_output.h"
 
-static void ftrace_dump_buf(int skip_lines, long cpu_file)
+static int ftrace_dump_buf(int skip_lines, long cpu_file, bool quiet)
 {
 	/* use static because iter can be a bit big for the stack */
 	static struct trace_iterator iter;

@@ -39,7 +39,9 @@ static void ftrace_dump_buf(int skip_lines, long cpu_file)
 	/* don't look at user memory in panic mode */
 	tr->trace_flags &= ~TRACE_ITER_SYM_USEROBJ;
 
-	kdb_printf("Dumping ftrace buffer:\n");
+	if (!quiet)
+		kdb_printf("Dumping ftrace buffer (skipping %d lines):\n",
+			   skip_lines);
 
 	/* reset all but tr, trace, and overruns */
 	memset(&iter.seq, 0,

@@ -66,25 +68,29 @@ static void ftrace_dump_buf(int skip_lines, long cpu_file)
 	}
 
 	while (trace_find_next_entry_inc(&iter)) {
-		if (!cnt)
-			kdb_printf("---------------------------------\n");
-		cnt++;
-
-		if (!skip_lines) {
-			print_trace_line(&iter);
-			trace_printk_seq(&iter.seq);
-		} else {
-			skip_lines--;
+		if (!quiet) {
+			if (!cnt)
+				kdb_printf("---------------------------------\n");
+
+			if (!skip_lines) {
+				print_trace_line(&iter);
+				trace_printk_seq(&iter.seq);
+			} else {
+				skip_lines--;
+			}
 		}
+		cnt++;
 
 		if (KDB_FLAG(CMD_INTERRUPT))
 			goto out;
 	}
 
-	if (!cnt)
-		kdb_printf("   (ftrace buffer empty)\n");
-	else
-		kdb_printf("---------------------------------\n");
+	if (!quiet) {
+		if (!cnt)
+			kdb_printf("   (ftrace buffer empty)\n");
+		else
+			kdb_printf("---------------------------------\n");
+	}
 
 out:
 	tr->trace_flags = old_userobj;

@@ -99,6 +105,8 @@ static void ftrace_dump_buf(int skip_lines, long cpu_file)
 			iter.buffer_iter[cpu] = NULL;
 		}
 	}
+
+	return cnt;
 }
 
 /*

@@ -109,6 +117,7 @@ static int kdb_ftdump(int argc, const char **argv)
 	int skip_lines = 0;
 	long cpu_file;
 	char *cp;
+	int count;
 
 	if (argc > 2)
 		return KDB_ARGCOUNT;

@@ -129,7 +138,14 @@ static int kdb_ftdump(int argc, const char **argv)
 	}
 
 	kdb_trap_printk++;
-	ftrace_dump_buf(skip_lines, cpu_file);
+
+	/* A negative skip_lines means skip all but the last lines */
+	if (skip_lines < 0) {
+		count = ftrace_dump_buf(0, cpu_file, true);
+		skip_lines = max(count + skip_lines, 0);
+	}
+
+	count = ftrace_dump_buf(skip_lines, cpu_file, false);
 	kdb_trap_printk--;
 
 	return 0;

@@ -138,7 +154,8 @@ static int kdb_ftdump(int argc, const char **argv)
 static __init int kdb_ftrace_register(void)
 {
 	kdb_register_flags("ftdump", kdb_ftdump, "[skip_#lines] [cpu]",
-			    "Dump ftrace log", 0, KDB_ENABLE_ALWAYS_SAFE);
+			    "Dump ftrace log; -skip dumps last #lines", 0,
+			    KDB_ENABLE_ALWAYS_SAFE);
 	return 0;
 }