From: "Steven Rostedt (VMware)" rostedt@goodmis.org

The ring buffer is made up of a link list of pages. When making the ring buffer bigger, it will allocate all the pages it needs before adding to the ring buffer, and if it fails, it frees them and returns an error. This makes increasing the ring buffer size an all or nothing action. When this was first created, the pages were allocated with "NORETRY". This was to not cause any Out-Of-Memory (OOM) actions from allocating the ring buffer. But NORETRY was too strict, as the ring buffer would fail to expand even when there's memory available, but was taken up in the page cache.

Commit 848618857d253 ("tracing/ring_buffer: Try harder to allocate") changed the allocating from NORETRY to RETRY_MAYFAIL. The RETRY_MAYFAIL would allocate from the page cache, but if there was no memory available, it would simple fail the allocation and not trigger an OOM.

This worked fine, but had one problem. As the ring buffer would allocate one page at a time, it could take up all memory in the system before it failed to allocate and free that memory. If the allocation is happening and the ring buffer allocates all memory and then tries to take more than available, its allocation will not trigger an OOM, but if there's any allocation that happens someplace else, that could trigger an OOM, even though once the ring buffer's allocation fails, it would free up all the previous memory it tried to allocate, and allow other memory allocations to succeed.

Commit d02bd27bd33dd ("mm/page_alloc.c: calculate 'available' memory in a separate function") separated out si_mem_availble() as a separate function that could be used to see how much memory is available in the system. Using this function to make sure that the ring buffer could be allocated before it tries to allocate pages we can avoid allocating all memory in the system and making it vulnerable to OOMs if other allocations are taking place.

Link: http://lkml.kernel.org/r/1522320104-6573-1-git-send-email-zhaoyang.huang@spr...

CC: stable@vger.kernel.org Cc: linux-mm@kvack.org Fixes: 848618857d253 ("tracing/ring_buffer: Try harder to allocate") Requires: d02bd27bd33dd ("mm/page_alloc.c: calculate 'available' memory in a separate function") Reported-by: Zhaoyang Huang huangzhaoyang@gmail.com Tested-by: Joel Fernandes joelaf@google.com Signed-off-by: Steven Rostedt (VMware) rostedt@goodmis.org --- kernel/trace/ring_buffer.c | 5 +++++ 1 file changed, 5 insertions(+)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 515be03e3009..966128f02121 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -1164,6 +1164,11 @@ static int __rb_allocate_pages(long nr_pages, struct list_head *pages, int cpu) struct buffer_page *bpage, *tmp; long i;

+ /* Check if the available memory is there first */ + i = si_mem_available(); + if (i < nr_pages) + return -ENOMEM; + for (i = 0; i < nr_pages; i++) { struct page *page; /*