[RFC] fprobe call of rethook_try_get faults

[Jiri Olsa]

hi,
I occasionally get following fault:

  general protection fault, probably for non-canonical address 0x6b6b6b6b6b6b6b6b: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC NOPTI
  CPU: 3 PID: 28438 Comm: test_progs Tainted: G           OE      6.4.0-rc3+ #448 dad92bc91c459c664b308990ada0799837010e31
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-1.fc37 04/01/2014
  RIP: 0010:rethook_try_get+0x34/0xf0
  Code: 48 8b 47 08 85 d2 74 0b 65 8b 15 af 26 eb 7e 85 d2 74 57 48 85 c0 74 73 e8 39 8e f0 ff 84 c0 74 6a 48 8b 53 10 48 85 d2 74 >
  RSP: 0018:ffffc90003ccfcf0 EFLAGS: 00010202
  RAX: 0000000000000001 RBX: ffff88810920db40 RCX: 0000000000000003
  RDX: 6b6b6b6b6b6b6b6b RSI: ffffffff82c0a371 RDI: ffffffff82bcbddb
  RBP: ffffffff81f5a5f0 R08: 0000000000000001 R09: 0000000000000000
  R10: 0000000000000000 R11: 0000000000014000 R12: ffffffffa02ec3f2
  R13: fffffffffffffff7 R14: ffffc90003ccfd38 R15: 0000000000000000
  FS:  00007f2f8195eb80(0000) GS:ffff88846da00000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: 00007f2f819c0140 CR3: 0000000189cb8006 CR4: 0000000000770ee0
  PKRU: 55555554
  Call Trace:
   <TASK>
   fprobe_handler+0xc1/0x270
   ? __pfx_bpf_testmod_init+0x10/0x10 [bpf_testmod b0bc3019aa6d6bdb2afc30cf6381f510d7e5abbe]
   ? __pfx_bpf_testmod_init+0x10/0x10 [bpf_testmod b0bc3019aa6d6bdb2afc30cf6381f510d7e5abbe]
   ? bpf_fentry_test1+0x5/0x10
   ? bpf_fentry_test1+0x5/0x10
   ? bpf_testmod_init+0x22/0x80 [bpf_testmod b0bc3019aa6d6bdb2afc30cf6381f510d7e5abbe]
   ? do_one_initcall+0x63/0x2e0
   ? rcu_is_watching+0xd/0x40
   ? kmalloc_trace+0xaf/0xc0
   ? do_init_module+0x60/0x250
   ? __do_sys_finit_module+0xac/0x120
   ? do_syscall_64+0x37/0x90
   ? entry_SYSCALL_64_after_hwframe+0x72/0xdc
   </TASK>
  Modules linked in: bpf_testmod(OE+) loop bpf_preload intel_rapl_msr intel_rapl_common crct10dif_pclmul crc32_pclmul crc32c_intel >


I can't really reliable reproduce this, but while checking the code, I wonder
we should call rethook_free only after we call unregister_ftrace_function like
in the patch below

jirka


---
diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
index 18d36842faf5..0121e8c0d54e 100644
--- a/kernel/trace/fprobe.c
+++ b/kernel/trace/fprobe.c
@@ -364,19 +364,13 @@ int unregister_fprobe(struct fprobe *fp)
 		    fp->ops.saved_func != fprobe_kprobe_handler))
 		return -EINVAL;
 
-	/*
-	 * rethook_free() starts disabling the rethook, but the rethook handlers
-	 * may be running on other processors at this point. To make sure that all
-	 * current running handlers are finished, call unregister_ftrace_function()
-	 * after this.
-	 */
-	if (fp->rethook)
-		rethook_free(fp->rethook);
-
 	ret = unregister_ftrace_function(&fp->ops);
 	if (ret < 0)
 		return ret;
 
+	if (fp->rethook)
+		rethook_free(fp->rethook);
+
 	ftrace_free_filter(&fp->ops);
 
 	return ret;