linux-kernel - [PATCH] init/main.c: fix boot time tracing crash

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Message-ID: <20250824130759.1732736-1-rppt@kernel.org>
Date: Sun, 24 Aug 2025 16:07:59 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mike Rapoport <rppt@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	linux-trace-kernel@...r.kernel.org,
	x86@...nel.org
Subject: [PATCH] init/main.c: fix boot time tracing crash

From: "Mike Rapoport (Microsoft)" <rppt@...nel.org>

Steven Rostedt reported a crash with "ftrace=function" kernel command
line:

[    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)
[ 0.166186] Code: 90 90 90 f3 0f 1e fa 0f 1f 44 00 00 55 48 89 e5 41 57 41 56 41 55 41 54 49 89 fc 53 48 83 e4 f0 48 83 ec 20 8b 05 c9 b6 7e 01 <44> 8b 77 1c 65 4c 8b 2d b5 ea 20 02 4c 89 6c 24 18 41 89 f5 21 f0
[    0.168811] RSP: 0000:ffffffffb2e03b30 EFLAGS: 00010086
[    0.169545] RAX: 0000000001fff33f RBX: 0000000000000000 RCX: 0000000000000000
[    0.170544] RDX: 0000000000002800 RSI: 0000000000002800 RDI: 0000000000000000
[    0.171554] RBP: ffffffffb2e03b80 R08: 0000000000000004 R09: ffffffffb2e03c90
[    0.172549] R10: ffffffffb2e03c90 R11: 0000000000000000 R12: 0000000000000000
[    0.173544] R13: ffffffffb2e03c90 R14: ffffffffb2e03c90 R15: 0000000000000001
[    0.174542] FS:  0000000000000000(0000) GS:ffff9d2808114000(0000) knlGS:0000000000000000
[    0.175684] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    0.176486] CR2: 000000000000001c CR3: 000000007264c001 CR4: 00000000000200b0
[    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 ]---

The crash happens because on x86 ftrace allocations from execmem require
maple tree to be initialized.

Move maple tree initialization that depends only on slab availability
earlier in boot so that it will happen right after mm_core_init().

Fixes: 5d79c2be5081 ("x86/ftrace: enable EXECMEM_ROX_CACHE for ftrace allocations")
Signed-off-by: Mike Rapoport (Microsoft) <rppt@...nel.org>
---
 init/main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

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

base-commit: c17b750b3ad9f45f2b6f7e6f7f4679844244f0b9
-- 
2.50.1