ring-buffer: fix dangling commit race (a8ccf1d6) · Commits · 戴 / test

Impact: fix stuck trace-buffers If an interrupt comes in during the rb_set_commit_to_write and pushes the tail page forward just at the right time, the commit updates will miss the adding of the interrupt data. This will cause the commit pointer to cease from moving forward. Thanks to Jiaying Zhang for finding this race. Reported-by:

Jiaying Zhang <jiayingz@google.com> Signed-off-by:

Steven Rostedt <srostedt@redhat.com> Cc: <stable@kernel.org> Signed-off-by:

Ingo Molnar <mingo@elte.hu>

kernel/trace/ring_buffer.c

+12 −0

Original line number	Diff line number	Diff line
		@@ -838,6 +838,7 @@ rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
		* back to us). This allows us to do a simple loop to
		* assign the commit to the tail.
		*/
		again:
		while (cpu_buffer->commit_page != cpu_buffer->tail_page) {
		cpu_buffer->commit_page->page->commit =
		cpu_buffer->commit_page->write;
		@@ -853,6 +854,17 @@ rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
		cpu_buffer->commit_page->write;
		barrier();
		}

		/* again, keep gcc from optimizing */
		barrier();

		/*
		* If an interrupt came in just after the first while loop
		* and pushed the tail page forward, we will be left with
		* a dangling commit that will never go forward.
		*/
		if (unlikely(cpu_buffer->commit_page != cpu_buffer->tail_page))
		goto again;
		}

		static void rb_reset_reader_page(struct ring_buffer_per_cpu *cpu_buffer)

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