Commit aa997d2d authored by Steven Rostedt's avatar Steven Rostedt Committed by Steven Rostedt (Google)
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ring-buffer: Do not warn in ring_buffer_map_get_reader() when reader catches up 



The function ring_buffer_map_get_reader() is a bit more strict than the
other get reader functions, and except for certain situations the
rb_get_reader_page() should not return NULL. If it does, it triggers a
warning.

This warning was triggering but after looking at why, it was because
another acceptable situation was happening and it wasn't checked for.

If the reader catches up to the writer and there's still data to be read
on the reader page, then the rb_get_reader_page() will return NULL as
there's no new page to get.

In this situation, the reader page should not be updated and no warning
should trigger.

Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Vincent Donnefort <vdonnefort@google.com>
Reported-by: default avatar <syzbot+92a3745cea5ec6360309@syzkaller.appspotmail.com>
Closes: https://lore.kernel.org/all/690babec.050a0220.baf87.0064.GAE@google.com/
Link: https://lore.kernel.org/20251016132848.1b11bb37@gandalf.local.home


Fixes: 117c3920 ("ring-buffer: Introducing ring-buffer mapping functions")
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent dcb6fa37

kernel/trace/ring_buffer.c

+4 −0
Original line number Diff line number Diff line
@@ -7344,6 +7344,10 @@ int ring_buffer_map_get_reader(struct trace_buffer *buffer, int cpu) 
		goto out;

	}



	/* Did the reader catch up with the writer? */

	if (cpu_buffer->reader_page == cpu_buffer->commit_page)

		goto out;



	reader = rb_get_reader_page(cpu_buffer);

	if (WARN_ON(!reader))

		goto out;