From a7e52ad7ed82e21273eccff93d1477a7b313aabb Mon Sep 17 00:00:00 2001 From: "Steven Rostedt (VMware)" Date: Wed, 2 Aug 2017 14:20:54 -0400 Subject: ring-buffer: Have ring_buffer_alloc_read_page() return error on offline CPU Chunyu Hu reported: "per_cpu trace directories and files are created for all possible cpus, but only the cpus which have ever been on-lined have their own per cpu ring buffer (allocated by cpuhp threads). While trace_buffers_open, the open handler for trace file 'trace_pipe_raw' is always trying to access field of ring_buffer_per_cpu, and would panic with the NULL pointer. Align the behavior of trace_pipe_raw with trace_pipe, that returns -NODEV when openning it if that cpu does not have trace ring buffer. Reproduce: cat /sys/kernel/debug/tracing/per_cpu/cpu31/trace_pipe_raw (cpu31 is never on-lined, this is a 16 cores x86_64 box) Tested with: 1) boot with maxcpus=14, read trace_pipe_raw of cpu15. Got -NODEV. 2) oneline cpu15, read trace_pipe_raw of cpu15. Get the raw trace data. Call trace: [ 5760.950995] RIP: 0010:ring_buffer_alloc_read_page+0x32/0xe0 [ 5760.961678] tracing_buffers_read+0x1f6/0x230 [ 5760.962695] __vfs_read+0x37/0x160 [ 5760.963498] ? __vfs_read+0x5/0x160 [ 5760.964339] ? security_file_permission+0x9d/0xc0 [ 5760.965451] ? __vfs_read+0x5/0x160 [ 5760.966280] vfs_read+0x8c/0x130 [ 5760.967070] SyS_read+0x55/0xc0 [ 5760.967779] do_syscall_64+0x67/0x150 [ 5760.968687] entry_SYSCALL64_slow_path+0x25/0x25" This was introduced by the addition of the feature to reuse reader pages instead of re-allocating them. The problem is that the allocation of a reader page (which is per cpu) does not check if the cpu is online and set up for the ring buffer. Link: http://lkml.kernel.org/r/1500880866-1177-1-git-send-email-chuhu@redhat.com Cc: stable@vger.kernel.org Fixes: 73a757e63114 ("ring-buffer: Return reader page back into existing ring buffer") Reported-by: Chunyu Hu Signed-off-by: Steven Rostedt (VMware) --- kernel/trace/ring_buffer_benchmark.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel/trace/ring_buffer_benchmark.c') diff --git a/kernel/trace/ring_buffer_benchmark.c b/kernel/trace/ring_buffer_benchmark.c index 9fbcaf567886..68ee79afe31c 100644 --- a/kernel/trace/ring_buffer_benchmark.c +++ b/kernel/trace/ring_buffer_benchmark.c @@ -113,7 +113,7 @@ static enum event_status read_page(int cpu) int i; bpage = ring_buffer_alloc_read_page(buffer, cpu); - if (!bpage) + if (IS_ERR(bpage)) return EVENT_DROPPED; ret = ring_buffer_read_page(buffer, &bpage, PAGE_SIZE, cpu, 1); -- cgit v1.2.3