This is a note to let you know that I've just added the patch titled ftrace: do CPU checking after preemption disabled to the 5.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: ftrace-do-cpu-checking-after-preemption-disabled.patch and it can be found in the queue-5.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 881e9a510519ad50013073a98177867bcced40aa Author: 王贇 <yun.wang@xxxxxxxxxxxxxxxxx> Date: Wed Oct 27 11:15:11 2021 +0800 ftrace: do CPU checking after preemption disabled [ Upstream commit d33cc657372366a8959f099c619a208b4c5dc664 ] With CONFIG_DEBUG_PREEMPT we observed reports like: BUG: using smp_processor_id() in preemptible caller is perf_ftrace_function_call+0x6f/0x2e0 CPU: 1 PID: 680 Comm: a.out Not tainted Call Trace: <TASK> dump_stack_lvl+0x8d/0xcf check_preemption_disabled+0x104/0x110 ? optimize_nops.isra.7+0x230/0x230 ? text_poke_bp_batch+0x9f/0x310 perf_ftrace_function_call+0x6f/0x2e0 ... __text_poke+0x5/0x620 text_poke_bp_batch+0x9f/0x310 This telling us the CPU could be changed after task is preempted, and the checking on CPU before preemption will be invalid. Since now ftrace_test_recursion_trylock() will help to disable the preemption, this patch just do the checking after trylock() to address the issue. Link: https://lkml.kernel.org/r/54880691-5fe2-33e7-d12f-1fa6136f5183@xxxxxxxxxxxxxxxxx CC: Steven Rostedt <rostedt@xxxxxxxxxxx> Cc: Guo Ren <guoren@xxxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: "James E.J. Bottomley" <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> Cc: Helge Deller <deller@xxxxxx> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx> Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> Cc: Paul Mackerras <paulus@xxxxxxxxx> Cc: Paul Walmsley <paul.walmsley@xxxxxxxxxx> Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx> Cc: Albert Ou <aou@xxxxxxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> Cc: Jiri Kosina <jikos@xxxxxxxxxx> Cc: Miroslav Benes <mbenes@xxxxxxx> Cc: Petr Mladek <pmladek@xxxxxxxx> Cc: Joe Lawrence <joe.lawrence@xxxxxxxxxx> Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx> Cc: "Peter Zijlstra (Intel)" <peterz@xxxxxxxxxxxxx> Cc: Nicholas Piggin <npiggin@xxxxxxxxx> Cc: Jisheng Zhang <jszhang@xxxxxxxxxx> Reported-by: Abaci <abaci@xxxxxxxxxxxxxxxxx> Signed-off-by: Michael Wang <yun.wang@xxxxxxxxxxxxxxxxx> Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c index 03be4435d103f..50cd5a1a7ab4a 100644 --- a/kernel/trace/trace_event_perf.c +++ b/kernel/trace/trace_event_perf.c @@ -441,13 +441,13 @@ perf_ftrace_function_call(unsigned long ip, unsigned long parent_ip, if (!rcu_is_watching()) return; - if ((unsigned long)ops->private != smp_processor_id()) - return; - bit = ftrace_test_recursion_trylock(ip, parent_ip); if (bit < 0) return; + if ((unsigned long)ops->private != smp_processor_id()) + goto out; + event = container_of(ops, struct perf_event, ftrace_ops); /*