function tracing: fix wrong position computing of stack_trace (522a110b) · Commits · 戴 / test

Impact: make output of stack_trace complete if buffer overruns When read buffer overruns, the output of stack_trace isn't complete. When printing records with seq_printf in t_show, if the read buffer has overruned by the current record, then this record won't be printed to user space through read buffer, it will just be dropped in this printing. When next printing, t_start should return the "*pos"th record, which is the one dropped by previous printing, but it just returns (m->private + *pos)th record. Here we use a more sane method to implement seq_operations which can be found in kernel code. Thus we needn't initialize m->private. About testing, it's not easy to overrun read buffer, but we can use seq_printf to print more padding bytes in t_show, then it's easy to check whether or not records are lost. This commit has been tested on both condition of overrun and non overrun. Signed-off-by:

Liming Wang <liming.wang@windriver.com> Acked-by:

Steven Rostedt <rostedt@goodmis.org> Signed-off-by:

Ingo Molnar <mingo@elte.hu>

kernel/trace/trace_stack.c

+15 −9

Original line number	Diff line number	Diff line
		@@ -184,11 +184,16 @@ static struct file_operations stack_max_size_fops = {
		static void *
		t_next(struct seq_file m, void v, loff_t *pos)
		{
		long i = (long)m->private;
		long i;

		(*pos)++;

		if (v == SEQ_START_TOKEN)
		i = 0;
		else {
		i = (long )v;
		i++;
		}

		if (i >= max_stack_trace.nr_entries \|\|
		stack_dump_trace[i] == ULONG_MAX)
		@@ -201,12 +206,15 @@ t_next(struct seq_file m, void v, loff_t *pos)

		static void t_start(struct seq_file m, loff_t *pos)
		{
		void *t = &m->private;
		void *t = SEQ_START_TOKEN;
		loff_t l = 0;

		local_irq_disable();
		__raw_spin_lock(&max_stack_lock);

		if (*pos == 0)
		return SEQ_START_TOKEN;

		for (; t && l < *pos; t = t_next(m, t, &l))
		;

		@@ -235,10 +243,10 @@ static int trace_lookup_stack(struct seq_file *m, long i)

		static int t_show(struct seq_file m, void v)
		{
		long i = (long )v;
		long i;
		int size;

		if (i < 0) {
		if (v == SEQ_START_TOKEN) {
		seq_printf(m, " Depth Size Location"
		" (%d entries)\n"
		" ----- ---- --------\n",
		@@ -246,6 +254,8 @@ static int t_show(struct seq_file m, void v)
		return 0;
		}

		i = (long )v;

		if (i >= max_stack_trace.nr_entries \|\|
		stack_dump_trace[i] == ULONG_MAX)
		return 0;
		@@ -275,10 +285,6 @@ static int stack_trace_open(struct inode inode, struct file file)
		int ret;

		ret = seq_open(file, &stack_trace_seq_ops);
		if (!ret) {
		struct seq_file *m = file->private_data;
		m->private = (void *)-1;
		}

		return ret;
		}

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