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Commit a7e52ad7 authored by Steven Rostedt (VMware)'s avatar Steven Rostedt (VMware)
Browse files

ring-buffer: Have ring_buffer_alloc_read_page() return error on offline CPU 

Chunyu Hu reported:
  "per_cpu trace directories and files are created for all possible cpus,
   but only the cpus which have ever been on-lined have their own per cpu
   ring buffer (allocated by cpuhp threads). While trace_buffers_open, the
   open handler for trace file 'trace_pipe_raw' is always trying to access
   field of ring_buffer_per_cpu, and would panic with the NULL pointer.

   Align the behavior of trace_pipe_raw with trace_pipe, that returns -NODEV
   when openning it if that cpu does not have trace ring buffer.

   Reproduce:
   cat /sys/kernel/debug/tracing/per_cpu/cpu31/trace_pipe_raw
   (cpu31 is never on-lined, this is a 16 cores x86_64 box)

   Tested with:
   1) boot with maxcpus=14, read trace_pipe_raw of cpu15.
      Got -NODEV.
   2) oneline cpu15, read trace_pipe_raw of cpu15.
      Get the raw trace data.

   Call trace:
   [ 5760.950995] RIP: 0010:ring_buffer_alloc_read_page+0x32/0xe0
   [ 5760.961678]  tracing_buffers_read+0x1f6/0x230
   [ 5760.962695]  __vfs_read+0x37/0x160
   [ 5760.963498]  ? __vfs_read+0x5/0x160
   [ 5760.964339]  ? security_file_permission+0x9d/0xc0
   [ 5760.965451]  ? __vfs_read+0x5/0x160
   [ 5760.966280]  vfs_read+0x8c/0x130
   [ 5760.967070]  SyS_read+0x55/0xc0
   [ 5760.967779]  do_syscall_64+0x67/0x150
   [ 5760.968687]  entry_SYSCALL64_slow_path+0x25/0x25"

This was introduced by the addition of the feature to reuse reader pages
instead of re-allocating them. The problem is that the allocation of a
reader page (which is per cpu) does not check if the cpu is online and set
up for the ring buffer.

Link: http://lkml.kernel.org/r/1500880866-1177-1-git-send-email-chuhu@redhat.com



Cc: stable@vger.kernel.org
Fixes: 73a757e6 ("ring-buffer: Return reader page back into existing ring buffer")
Reported-by: default avatarChunyu Hu <chuhu@redhat.com>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 147d88e0

kernel/trace/ring_buffer.c

+9 −5
Original line number Diff line number Diff line
@@ -4386,15 +4386,19 @@ EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu); 
 * the page that was allocated, with the read page of the buffer.

 *

 * Returns:

 *  The page allocated, or NULL on error.

 *  The page allocated, or ERR_PTR

 */

void *ring_buffer_alloc_read_page(struct ring_buffer *buffer, int cpu)

{

	struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];

	struct ring_buffer_per_cpu *cpu_buffer;

	struct buffer_data_page *bpage = NULL;

	unsigned long flags;

	struct page *page;



	if (!cpumask_test_cpu(cpu, buffer->cpumask))

		return ERR_PTR(-ENODEV);



	cpu_buffer = buffer->buffers[cpu];

	local_irq_save(flags);

	arch_spin_lock(&cpu_buffer->lock);
@@ -4412,7 +4416,7 @@ void *ring_buffer_alloc_read_page(struct ring_buffer *buffer, int cpu) 
	page = alloc_pages_node(cpu_to_node(cpu),

				GFP_KERNEL | __GFP_NORETRY, 0);

	if (!page)

		return NULL;

		return ERR_PTR(-ENOMEM);



	bpage = page_address(page);
@@ -4467,8 +4471,8 @@ EXPORT_SYMBOL_GPL(ring_buffer_free_read_page); 
 *

 * for example:

 *	rpage = ring_buffer_alloc_read_page(buffer, cpu);

 *	if (!rpage)

 *		return error;

 *	if (IS_ERR(rpage))

 *		return PTR_ERR(rpage);

 *	ret = ring_buffer_read_page(buffer, &rpage, len, cpu, 0);

 *	if (ret >= 0)

 *		process_page(rpage, ret);

kernel/trace/ring_buffer_benchmark.c

+1 −1
Original line number Diff line number Diff line
@@ -113,7 +113,7 @@ static enum event_status read_page(int cpu) 
	int i;



	bpage = ring_buffer_alloc_read_page(buffer, cpu);

	if (!bpage)

	if (IS_ERR(bpage))

		return EVENT_DROPPED;



	ret = ring_buffer_read_page(buffer, &bpage, PAGE_SIZE, cpu, 1);

kernel/trace/trace.c

+11 −5
Original line number Diff line number Diff line
@@ -6598,7 +6598,7 @@ tracing_buffers_read(struct file *filp, char __user *ubuf, 
{

	struct ftrace_buffer_info *info = filp->private_data;

	struct trace_iterator *iter = &info->iter;

	ssize_t ret;

	ssize_t ret = 0;

	ssize_t size;



	if (!count)
@@ -6612,10 +6612,15 @@ tracing_buffers_read(struct file *filp, char __user *ubuf, 
	if (!info->spare) {

		info->spare = ring_buffer_alloc_read_page(iter->trace_buffer->buffer,

							  iter->cpu_file);

		if (IS_ERR(info->spare)) {

			ret = PTR_ERR(info->spare);

			info->spare = NULL;

		} else {

			info->spare_cpu = iter->cpu_file;

		}

	}

	if (!info->spare)

		return -ENOMEM;

		return ret;



	/* Do we have previous read data to read? */

	if (info->read < PAGE_SIZE)
@@ -6790,8 +6795,9 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos, 
		ref->ref = 1;

		ref->buffer = iter->trace_buffer->buffer;

		ref->page = ring_buffer_alloc_read_page(ref->buffer, iter->cpu_file);

		if (!ref->page) {

			ret = -ENOMEM;

		if (IS_ERR(ref->page)) {

			ret = PTR_ERR(ref->page);

			ref->page = NULL;

			kfree(ref);

			break;

		}