From: Ravi Bangoria Kernel is crashing when user tries to record 'ftrace:function' event with empty filter: # perf record -e ftrace:function --filter="" ls # dmesg BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 Oops: 0000 [#1] SMP PTI ... RIP: 0010:ftrace_profile_set_filter+0x14b/0x2d0 RSP: 0018:ffffa4a7c0da7d20 EFLAGS: 00010246 RAX: ffffa4a7c0da7d64 RBX: 0000000000000000 RCX: 0000000000000006 RDX: 0000000000000000 RSI: 0000000000000092 RDI: ffff8c48ffc968f0 ... Call Trace: _perf_ioctl+0x54a/0x6b0 ? rcu_all_qs+0x5/0x30 ... After patch: # perf record -e ftrace:function --filter="" ls failed to set filter "" on event ftrace:function with 22 (Invalid argument) Also, if user tries to echo "" > filter, it used to throw an error. This behavior got changed by commit 80765597bc58 ("tracing: Rewrite filter logic to be simpler and faster"). This patch restores the behavior as a side effect: Before patch: # echo "" > filter # After patch: # echo "" > filter bash: echo: write error: Invalid argument # Link: http://lkml.kernel.org/r/20180420150758.19787-1-ravi.bangoria@linux.ibm.com Fixes: 80765597bc58 ("tracing: Rewrite filter logic to be simpler and faster") Signed-off-by: Ravi Bangoria Signed-off-by: Steven Rostedt (VMware) --- kernel/trace/trace_events_filter.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c index 9b4716bb8bb0..1f951b3df60c 100644 --- a/kernel/trace/trace_events_filter.c +++ b/kernel/trace/trace_events_filter.c @@ -1499,14 +1499,14 @@ static int process_preds(struct trace_event_call *call, return ret; } - if (!nr_preds) { - prog = NULL; - } else { - prog = predicate_parse(filter_string, nr_parens, nr_preds, + if (!nr_preds) + return -EINVAL; + + prog = predicate_parse(filter_string, nr_parens, nr_preds, parse_pred, call, pe); - if (IS_ERR(prog)) - return PTR_ERR(prog); - } + if (IS_ERR(prog)) + return PTR_ERR(prog); + rcu_assign_pointer(filter->prog, prog); return 0; } -- 2.16.3