block: make blktrace use per-cpu buffers for message notes

Currently it uses a single static char array, but that risks being corrupted when multiple users issue message notes at the same time. Make the buffers dynamically allocated when the trace is setup and make them per-cpu instead. The default max message size of 1k is also very large, the interface is mainly for small text notes. So shrink it to 128 bytes. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

block: make blktrace use per-cpu buffers for message notes
Currently it uses a single static char array, but that risks being corrupted when multiple users issue message notes at the same time. Make the buffers dynamically allocated when the trace is setup and make them per-cpu instead. The default max message size of 1k is also very large, the interface is mainly for small text notes. So shrink it to 128 bytes. Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
Jens Axboe
1 parent 4722dc52a8
Showing 2 changed files with 14 additions and 4 deletions Side-by-side Diff
block/blktrace.c
include/linux/blktrace_api.h
@@ -79,13 +79,16 @@
 {
 	int n;
 	va_list args;
-	static char bt_msg_buf[BLK_TN_MAX_MSG];
+	char *buf;
  
+	preempt_disable();
+	buf = per_cpu_ptr(bt->msg_data, smp_processor_id());
 	va_start(args, fmt);
-	n = vscnprintf(bt_msg_buf, BLK_TN_MAX_MSG, fmt, args);
+	n = vscnprintf(buf, BLK_TN_MAX_MSG, fmt, args);
 	va_end(args);
  
-	trace_note(bt, 0, BLK_TN_MESSAGE, bt_msg_buf, n);
+	trace_note(bt, 0, BLK_TN_MESSAGE, buf, n);
+	preempt_enable();
 }
 EXPORT_SYMBOL_GPL(__trace_note_message);
  
@@ -246,6 +249,7 @@
 	debugfs_remove(bt->dropped_file);
 	blk_remove_tree(bt->dir);
 	free_percpu(bt->sequence);
+	free_percpu(bt->msg_data);
 	kfree(bt);
 }
  
@@ -360,6 +364,10 @@
 	if (!bt->sequence)
 		goto err;
  
+	bt->msg_data = __alloc_percpu(BLK_TN_MAX_MSG);
+	if (!bt->msg_data)
+		goto err;
+
 	ret = -ENOENT;
 	dir = blk_create_tree(buts->name);
 	if (!dir)
@@ -406,6 +414,7 @@
 		if (bt->dropped_file)
 			debugfs_remove(bt->dropped_file);
 		free_percpu(bt->sequence);
+		free_percpu(bt->msg_data);
 		if (bt->rchan)
 			relay_close(bt->rchan);
 		kfree(bt);
@@ -121,6 +121,7 @@
 	int trace_state;
 	struct rchan *rchan;
 	unsigned long *sequence;
+	unsigned char *msg_data;
 	u16 act_mask;
 	u64 start_lba;
 	u64 end_lba;
@@ -172,7 +173,7 @@
 		if (unlikely(bt))					\
 			__trace_note_message(bt, fmt, ##__VA_ARGS__);	\
 	} while (0)
-#define BLK_TN_MAX_MSG		1024
+#define BLK_TN_MAX_MSG		128
  
 /**
  * blk_add_trace_rq - Add a trace for a request oriented action
...	...	@@ -79,13 +79,16 @@
79	79	{
80	80	int n;
81	81	va_list args;
82		- static char bt_msg_buf[BLK_TN_MAX_MSG];
	82	+ char *buf;
83	83
	84	+ preempt_disable();
	85	+ buf = per_cpu_ptr(bt->msg_data, smp_processor_id());
84	86	va_start(args, fmt);
85		- n = vscnprintf(bt_msg_buf, BLK_TN_MAX_MSG, fmt, args);
	87	+ n = vscnprintf(buf, BLK_TN_MAX_MSG, fmt, args);
86	88	va_end(args);
87	89
88		- trace_note(bt, 0, BLK_TN_MESSAGE, bt_msg_buf, n);
	90	+ trace_note(bt, 0, BLK_TN_MESSAGE, buf, n);
	91	+ preempt_enable();
89	92	}
90	93	EXPORT_SYMBOL_GPL(__trace_note_message);
91	94
...	...	@@ -246,6 +249,7 @@
246	249	debugfs_remove(bt->dropped_file);
247	250	blk_remove_tree(bt->dir);
248	251	free_percpu(bt->sequence);
	252	+ free_percpu(bt->msg_data);
249	253	kfree(bt);
250	254	}
251	255
...	...	@@ -360,6 +364,10 @@
360	364	if (!bt->sequence)
361	365	goto err;
362	366
	367	+ bt->msg_data = __alloc_percpu(BLK_TN_MAX_MSG);
	368	+ if (!bt->msg_data)
	369	+ goto err;
	370	+
363	371	ret = -ENOENT;
364	372	dir = blk_create_tree(buts->name);
365	373	if (!dir)
...	...	@@ -406,6 +414,7 @@
406	414	if (bt->dropped_file)
407	415	debugfs_remove(bt->dropped_file);
408	416	free_percpu(bt->sequence);
	417	+ free_percpu(bt->msg_data);
409	418	if (bt->rchan)
410	419	relay_close(bt->rchan);
411	420	kfree(bt);
...	...	@@ -121,6 +121,7 @@
121	121	int trace_state;
122	122	struct rchan *rchan;
123	123	unsigned long *sequence;
	124	+ unsigned char *msg_data;
124	125	u16 act_mask;
125	126	u64 start_lba;
126	127	u64 end_lba;
...	...	@@ -172,7 +173,7 @@
172	173	if (unlikely(bt)) \
173	174	__trace_note_message(bt, fmt, ##__VA_ARGS__); \
174	175	} while (0)
175		-#define BLK_TN_MAX_MSG 1024
	176	+#define BLK_TN_MAX_MSG 128
176	177
177	178	/**
178	179	* blk_add_trace_rq - Add a trace for a request oriented action