4.4-stable review patch. If anyone has any objections, please let me know.
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From: Vaibhav Nagarnaik vnagarnaik@google.com
commit 83f365554e47997ec68dc4eca3f5dce525cd15c3 upstream.
When reducing ring buffer size, pages are removed by scheduling a work item on each CPU for the corresponding CPU ring buffer. After the pages are removed from ring buffer linked list, the pages are free()d in a tight loop. The loop does not give up CPU until all pages are removed. In a worst case behavior, when lot of pages are to be freed, it can cause system stall.
After the pages are removed from the list, the free() can happen while the work is rescheduled. Call cond_resched() in the loop to prevent the system hangup.
Link: http://lkml.kernel.org/r/20180907223129.71994-1-vnagarnaik@google.com
Cc: stable@vger.kernel.org Fixes: 83f40318dab00 ("ring-buffer: Make removal of ring buffer pages atomic") Reported-by: Jason Behmer jbehmer@google.com Signed-off-by: Vaibhav Nagarnaik vnagarnaik@google.com Signed-off-by: Steven Rostedt (VMware) rostedt@goodmis.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/trace/ring_buffer.c | 2 ++ 1 file changed, 2 insertions(+)
--- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -1513,6 +1513,8 @@ rb_remove_pages(struct ring_buffer_per_c tmp_iter_page = first_page;
do { + cond_resched(); + to_remove_page = tmp_iter_page; rb_inc_page(cpu_buffer, &tmp_iter_page);