On Wed, Aug 20, 2025 at 06:47:43PM -0400, Steven Rostedt wrote:
> On Sun, 13 Jul 2025 10:17:30 +0300
> Mike Rapoport <r...@kernel.org> wrote:
>
> > From: "Mike Rapoport (Microsoft)" <r...@kernel.org>
> >
> > For the most part ftrace uses text poking and can handle ROX memory.
> > The only place that requires writable memory is create_trampoline() that
> > updates the allocated memory and in the end makes it ROX.
> >
> > Use execmem_alloc_rw() in x86::ftrace::alloc_tramp() and enable ROX cache
> > for EXECMEM_FTRACE when configuration and CPU features allow that.
> >
> > Acked-by: Peter Zijlstra (Intel) <pet...@infradead.org>
> > Signed-off-by: Mike Rapoport (Microsoft) <r...@kernel.org>
> > ---
>
> The "ftrace=function" kernel command line started crashing with v6.17-rc1,
> and I bisected it down to this commit:
>
> 5d79c2be5081 ("x86/ftrace: enable EXECMEM_ROX_CACHE for ftrace allocations")
>
> On boot I hit this:
>
> [ 0.159269] BUG: kernel NULL pointer dereference, address: 000000000000001c
> [ 0.160254] #PF: supervisor read access in kernel mode
> [ 0.160975] #PF: error_code(0x0000) - not-present page
> [ 0.161697] PGD 0 P4D 0
> [ 0.162055] Oops: Oops: 0000 [#1] SMP PTI
> [ 0.162619] CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted
> 6.17.0-rc2-test-00006-g48d06e78b7cb-dirty #9 PREEMPT(undef)
> [ 0.164141] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
> 1.16.3-debian-1.16.3-2 04/01/2014
> [ 0.165439] RIP: 0010:kmem_cache_alloc_noprof (mm/slub.c:4237)
> [ 0.177483] Call Trace:
> [ 0.177828] <TASK>
> [ 0.178123] mas_alloc_nodes (lib/maple_tree.c:176 (discriminator 2)
> lib/maple_tree.c:1255 (discriminator 2))
> [ 0.178692] mas_store_gfp (lib/maple_tree.c:5468)
> [ 0.179223] execmem_cache_add_locked (mm/execmem.c:207)
> [ 0.179870] execmem_alloc (mm/execmem.c:213 mm/execmem.c:313
> mm/execmem.c:335 mm/execmem.c:475)
> [ 0.180397] ? ftrace_caller (arch/x86/kernel/ftrace_64.S:169)
> [ 0.180922] ? __pfx_ftrace_caller (arch/x86/kernel/ftrace_64.S:158)
> [ 0.181517] execmem_alloc_rw (mm/execmem.c:487)
> [ 0.182052] arch_ftrace_update_trampoline (arch/x86/kernel/ftrace.c:266
> arch/x86/kernel/ftrace.c:344 arch/x86/kernel/ftrace.c:474)
> [ 0.182778] ? ftrace_caller_op_ptr (arch/x86/kernel/ftrace_64.S:182)
> [ 0.183388] ftrace_update_trampoline (kernel/trace/ftrace.c:7947)
> [ 0.184024] __register_ftrace_function (kernel/trace/ftrace.c:368)
> [ 0.184682] ftrace_startup (kernel/trace/ftrace.c:3048)
> [ 0.185205] ? __pfx_function_trace_call
> (kernel/trace/trace_functions.c:210)
> [ 0.185877] register_ftrace_function_nolock (kernel/trace/ftrace.c:8717)
> [ 0.186595] register_ftrace_function (kernel/trace/ftrace.c:8745)
> [ 0.187254] ? __pfx_function_trace_call
> (kernel/trace/trace_functions.c:210)
> [ 0.187924] function_trace_init (kernel/trace/trace_functions.c:170)
> [ 0.188499] tracing_set_tracer (kernel/trace/trace.c:5916
> kernel/trace/trace.c:6349)
> [ 0.189088] register_tracer (kernel/trace/trace.c:2391)
> [ 0.189642] early_trace_init (kernel/trace/trace.c:11075
> kernel/trace/trace.c:11149)
> [ 0.190204] start_kernel (init/main.c:970)
> [ 0.190732] x86_64_start_reservations (arch/x86/kernel/head64.c:307)
> [ 0.191381] x86_64_start_kernel (??:?)
> [ 0.191955] common_startup_64 (arch/x86/kernel/head_64.S:419)
> [ 0.192534] </TASK>
> [ 0.192839] Modules linked in:
> [ 0.193267] CR2: 000000000000001c
> [ 0.193730] ---[ end trace 0000000000000000 ]---
maple tree is initialized after ftrace, so the patch below should fix it:
diff --git a/init/main.c b/init/main.c
index 0ee0ee7b7c2c..5753e9539ae6 100644
--- a/init/main.c
+++ b/init/main.c
@@ -956,6 +956,7 @@ void start_kernel(void)
sort_main_extable();
trap_init();
mm_core_init();
+ maple_tree_init();
poking_init();
ftrace_init();
@@ -973,7 +974,6 @@ void start_kernel(void)
"Interrupts were enabled *very* early, fixing it\n"))
local_irq_disable();
radix_tree_init();
- maple_tree_init();
/*
* Set up housekeeping before setting up workqueues to allow the unbound
> -- Steve
--
Sincerely yours,
Mike.
