Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Fri,  7 Sep 2018 11:21:31 -0700
Message-Id: <20180907182131.144514-1-vnagarnaik@google.com>
Mime-Version: 1.0
Subject: [PATCH] ring-buffer: Allow for rescheduling when removing pages
From:   Vaibhav Nagarnaik <vnagarnaik@google.com>
To:     Steven Rostedt <rostedt@goodmis.org>
Cc:     linux-kernel@vger.kernel.org,
        Vaibhav Nagarnaik <vnagarnaik@google.com>, jbehmer@google.com
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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. Add a check for need_sched() within the loop
to prevent the system hangup.

Reported-by: Jason Behmer <jbehmer@google.com>
Signed-off-by: Vaibhav Nagarnaik <vnagarnaik@google.com>
---
 kernel/trace/ring_buffer.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index 1d92d4a982fd..bc1789df7c53 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1546,6 +1546,9 @@ rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned long nr_pages)
 	tmp_iter_page = first_page;
 
 	do {
+		if (need_resched())
+			schedule();
+
 		to_remove_page = tmp_iter_page;
 		rb_inc_page(cpu_buffer, &tmp_iter_page);
 
-- 
2.19.0.rc2.392.g5ba43deb5a-goog