[PATCH 0/2] tracing: Fix some bug about synth

[PATCH 0/2] tracing: Fix some bug about synth

[Shang XiaoJing]

Some bugs are found when insert synth_event_gen_test, and fixed by this
patch set. 

Shang XiaoJing (2):
  tracing: Fix memory leak in test_gen_synth_cmd() and
    test_empty_synth_event()
  tracing: Fix wild-memory-access in register_synth_event()

 kernel/trace/synth_event_gen_test.c | 2 ++
 kernel/trace/trace_events_synth.c   | 2 ++
 2 files changed, 4 insertions(+)

-- 
2.17.1

[PATCH 1/2] tracing: Fix memory leak in test_gen_synth_cmd() and test_empty_synth_event()

[Shang XiaoJing]

test_gen_synth_cmd() only free buf in fail path, hence buf will leak
when there is no failure. Add kfree(buf) to prevent the memleak. The
same reason and solution in test_empty_synth_event().

unreferenced object 0xffff8881127de000 (size 2048):
  comm "modprobe", pid 247, jiffies 4294972316 (age 78.756s)
  hex dump (first 32 bytes):
    20 67 65 6e 5f 73 79 6e 74 68 5f 74 65 73 74 20   gen_synth_test
    20 70 69 64 5f 74 20 6e 65 78 74 5f 70 69 64 5f   pid_t next_pid_
  backtrace:
    [<000000004254801a>] kmalloc_trace+0x26/0x100
    [<0000000039eb1cf5>] 0xffffffffa00083cd
    [<000000000e8c3bc8>] 0xffffffffa00086ba
    [<00000000c293d1ea>] do_one_initcall+0xdb/0x480
    [<00000000aa189e6d>] do_init_module+0x1cf/0x680
    [<00000000d513222b>] load_module+0x6a50/0x70a0
    [<000000001fd4d529>] __do_sys_finit_module+0x12f/0x1c0
    [<00000000b36c4c0f>] do_syscall_64+0x3f/0x90
    [<00000000bbf20cf3>] entry_SYSCALL_64_after_hwframe+0x63/0xcd
unreferenced object 0xffff8881127df000 (size 2048):
  comm "modprobe", pid 247, jiffies 4294972324 (age 78.728s)
  hex dump (first 32 bytes):
    20 65 6d 70 74 79 5f 73 79 6e 74 68 5f 74 65 73   empty_synth_tes
    74 20 20 70 69 64 5f 74 20 6e 65 78 74 5f 70 69  t  pid_t next_pi
  backtrace:
    [<000000004254801a>] kmalloc_trace+0x26/0x100
    [<00000000d4db9a3d>] 0xffffffffa0008071
    [<00000000c31354a5>] 0xffffffffa00086ce
    [<00000000c293d1ea>] do_one_initcall+0xdb/0x480
    [<00000000aa189e6d>] do_init_module+0x1cf/0x680
    [<00000000d513222b>] load_module+0x6a50/0x70a0
    [<000000001fd4d529>] __do_sys_finit_module+0x12f/0x1c0
    [<00000000b36c4c0f>] do_syscall_64+0x3f/0x90
    [<00000000bbf20cf3>] entry_SYSCALL_64_after_hwframe+0x63/0xcd

Fixes: 9fe41efaca08 ("tracing: Add synth event generation test module")
Signed-off-by: Shang XiaoJing <shangxiaojing@huawei.com>
---
 kernel/trace/synth_event_gen_test.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/trace/synth_event_gen_test.c b/kernel/trace/synth_event_gen_test.c
index 0b15e975d2c2..db1ec4809ad1 100644
--- a/kernel/trace/synth_event_gen_test.c
+++ b/kernel/trace/synth_event_gen_test.c
@@ -120,6 +120,7 @@ static int __init test_gen_synth_cmd(void)
 
 	/* Now generate a gen_synth_test event */
 	ret = synth_event_trace_array(gen_synth_test, vals, ARRAY_SIZE(vals));
+	kfree(buf);
  out:
 	return ret;
  delete:
@@ -227,6 +228,7 @@ static int __init test_empty_synth_event(void)
 
 	/* Now trace an empty_synth_test event */
 	ret = synth_event_trace_array(empty_synth_test, vals, ARRAY_SIZE(vals));
+	kfree(buf);
  out:
 	return ret;
  delete:
-- 
2.17.1

[PATCH 2/2] tracing: Fix wild-memory-access in register_synth_event()

[Shang XiaoJing]

In register_synth_event(), if set_synth_event_print_fmt() failed, then
both trace_remove_event_call() and unregister_trace_event() will be
called. If call->event.funcs is not NULL, then the trace_event_call will
call __unregister_trace_event() twice. As the result, the second
__unregister_trace_event() will causes the wild-memory-access.

register_synth_event
    set_synth_event_print_fmt failed
    trace_remove_event_call
        event_remove
            if call->event.funcs then
            __unregister_trace_event (first call)
    unregister_trace_event
        __unregister_trace_event (second call)

Fix the bug by avoiding to call the second __unregister_trace_event() by
checking if the first one is called.

general protection fault, probably for non-canonical address
	0xfbd59c0000000024: 0000 [#1] SMP KASAN PTI
KASAN: maybe wild-memory-access in range
[0xdead000000000120-0xdead000000000127]
CPU: 0 PID: 3807 Comm: modprobe Not tainted
6.1.0-rc1-00186-g76f33a7eedb4 #299
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org 04/01/2014
RIP: 0010:unregister_trace_event+0x6e/0x280
Code: 00 fc ff df 4c 89 ea 48 c1 ea 03 80 3c 02 00 0f 85 0e 02 00 00 48
b8 00 00 00 00 00 fc ff df 4c 8b 63 08 4c 89 e2 48 c1 ea 03 <80> 3c 02
00 0f 85 e2 01 00 00 49 89 2c 24 48 85 ed 74 28 e8 7a 9b
RSP: 0018:ffff88810413f370 EFLAGS: 00010a06
RAX: dffffc0000000000 RBX: ffff888105d050b0 RCX: 0000000000000000
RDX: 1bd5a00000000024 RSI: ffff888119e276e0 RDI: ffffffff835a8b20
RBP: dead000000000100 R08: 0000000000000000 R09: fffffbfff0913481
R10: ffffffff8489a407 R11: fffffbfff0913480 R12: dead000000000122
R13: ffff888105d050b8 R14: 0000000000000000 R15: ffff888105d05028
FS:  00007f7823e8d540(0000) GS:ffff888119e00000(0000)
knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7823e7ebec CR3: 000000010a058002 CR4: 0000000000330ef0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 __create_synth_event+0x1e37/0x1eb0
 create_or_delete_synth_event+0x110/0x250
 synth_event_run_command+0x2f/0x110
 test_gen_synth_cmd+0x170/0x2eb [synth_event_gen_test]
 synth_event_gen_test_init+0x76/0x9bc [synth_event_gen_test]
 do_one_initcall+0xdb/0x480
 do_init_module+0x1cf/0x680
 load_module+0x6a50/0x70a0
 __do_sys_finit_module+0x12f/0x1c0
 do_syscall_64+0x3f/0x90
 entry_SYSCALL_64_after_hwframe+0x63/0xcd

Fixes: 4b147936fa50 ("tracing: Add support for 'synthetic' events")
Signed-off-by: Shang XiaoJing <shangxiaojing@huawei.com>
Cc: stable@vger.kernel.org
---
 kernel/trace/trace_events_synth.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
index e310052dc83c..a51280a153e3 100644
--- a/kernel/trace/trace_events_synth.c
+++ b/kernel/trace/trace_events_synth.c
@@ -830,6 +830,8 @@ static int register_synth_event(struct synth_event *event)
 	ret = set_synth_event_print_fmt(call);
 	if (ret < 0) {
 		trace_remove_event_call(call);
+		if (call->event.funcs)
+			return ret;
 		goto err;
 	}
  out:
-- 
2.17.1

Re: [PATCH 1/2] tracing: Fix memory leak in test_gen_synth_cmd() and test_empty_synth_event()

[Tom Zanussi]

Hi Shang,

Thanks for finding this bug, comment below...

On Tue, 2022-11-08 at 16:31 +0800, Shang XiaoJing wrote:
> test_gen_synth_cmd() only free buf in fail path, hence buf will leak
> when there is no failure. Add kfree(buf) to prevent the memleak. The
> same reason and solution in test_empty_synth_event().
> 
> unreferenced object 0xffff8881127de000 (size 2048):
>   comm "modprobe", pid 247, jiffies 4294972316 (age 78.756s)
>   hex dump (first 32 bytes):
>     20 67 65 6e 5f 73 79 6e 74 68 5f 74 65 73 74 20   gen_synth_test
>     20 70 69 64 5f 74 20 6e 65 78 74 5f 70 69 64 5f   pid_t next_pid_
>   backtrace:
>     [<000000004254801a>] kmalloc_trace+0x26/0x100
>     [<0000000039eb1cf5>] 0xffffffffa00083cd
>     [<000000000e8c3bc8>] 0xffffffffa00086ba
>     [<00000000c293d1ea>] do_one_initcall+0xdb/0x480
>     [<00000000aa189e6d>] do_init_module+0x1cf/0x680
>     [<00000000d513222b>] load_module+0x6a50/0x70a0
>     [<000000001fd4d529>] __do_sys_finit_module+0x12f/0x1c0
>     [<00000000b36c4c0f>] do_syscall_64+0x3f/0x90
>     [<00000000bbf20cf3>] entry_SYSCALL_64_after_hwframe+0x63/0xcd
> unreferenced object 0xffff8881127df000 (size 2048):
>   comm "modprobe", pid 247, jiffies 4294972324 (age 78.728s)
>   hex dump (first 32 bytes):
>     20 65 6d 70 74 79 5f 73 79 6e 74 68 5f 74 65 73   empty_synth_tes
>     74 20 20 70 69 64 5f 74 20 6e 65 78 74 5f 70 69  t  pid_t next_pi
>   backtrace:
>     [<000000004254801a>] kmalloc_trace+0x26/0x100
>     [<00000000d4db9a3d>] 0xffffffffa0008071
>     [<00000000c31354a5>] 0xffffffffa00086ce
>     [<00000000c293d1ea>] do_one_initcall+0xdb/0x480
>     [<00000000aa189e6d>] do_init_module+0x1cf/0x680
>     [<00000000d513222b>] load_module+0x6a50/0x70a0
>     [<000000001fd4d529>] __do_sys_finit_module+0x12f/0x1c0
>     [<00000000b36c4c0f>] do_syscall_64+0x3f/0x90
>     [<00000000bbf20cf3>] entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> Fixes: 9fe41efaca08 ("tracing: Add synth event generation test
> module")
> Signed-off-by: Shang XiaoJing <shangxiaojing@huawei.com>
> ---
>  kernel/trace/synth_event_gen_test.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/trace/synth_event_gen_test.c
> b/kernel/trace/synth_event_gen_test.c
> index 0b15e975d2c2..db1ec4809ad1 100644
> --- a/kernel/trace/synth_event_gen_test.c
> +++ b/kernel/trace/synth_event_gen_test.c
> @@ -120,6 +120,7 @@ static int __init test_gen_synth_cmd(void)
>  
>         /* Now generate a gen_synth_test event */
>         ret = synth_event_trace_array(gen_synth_test, vals,
> ARRAY_SIZE(vals));
> +       kfree(buf);
>   out:
>         return ret;
>   delete:
> @@ -227,6 +228,7 @@ static int __init test_empty_synth_event(void)
>  
>         /* Now trace an empty_synth_test event */
>         ret = synth_event_trace_array(empty_synth_test, vals,
> ARRAY_SIZE(vals));
> +       kfree(buf);
>   out:
>         return ret;
>   delete:

Makes sense, and if you do this then you could probably remove the
other kfree() at the bottom and clean the code up a bit, like change
this:

       /* Now generate a gen_synth_test event */
       ret = synth_event_trace_array(gen_synth_test, vals, ARRAY_SIZE(vals));
       kfree(buf);
 out:
        return ret;
 delete:
        /* We got an error after creating the event, delete it */
	synth_event_delete("gen_synth_test");
 free:
        kfree(buf);

	goto out;
}

to this:

       /* Now generate a gen_synth_test event */
       ret = synth_event_trace_array(gen_synth_test, vals, ARRAY_SIZE(vals));
 free:
       kfree(buf);
       return ret;
 delete:
        /* We got an error after creating the event, delete it */
	synth_event_delete("gen_synth_test");
 	goto free;
}

What do you think?

Tom

Re: [PATCH 2/2] tracing: Fix wild-memory-access in register_synth_event()

[Tom Zanussi]

Hi Shang,

On Tue, 2022-11-08 at 16:31 +0800, Shang XiaoJing wrote:
> In register_synth_event(), if set_synth_event_print_fmt() failed, then
> both trace_remove_event_call() and unregister_trace_event() will be
> called. If call->event.funcs is not NULL, then the trace_event_call will
> call __unregister_trace_event() twice. As the result, the second
> __unregister_trace_event() will causes the wild-memory-access.
> 
> register_synth_event
>     set_synth_event_print_fmt failed
>     trace_remove_event_call
>         event_remove
>             if call->event.funcs then
>             __unregister_trace_event (first call)
>     unregister_trace_event
>         __unregister_trace_event (second call)
> 
> Fix the bug by avoiding to call the second __unregister_trace_event() by
> checking if the first one is called.
> 
> general protection fault, probably for non-canonical address
>         0xfbd59c0000000024: 0000 [#1] SMP KASAN PTI
> KASAN: maybe wild-memory-access in range
> [0xdead000000000120-0xdead000000000127]
> CPU: 0 PID: 3807 Comm: modprobe Not tainted
> 6.1.0-rc1-00186-g76f33a7eedb4 #299
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org 04/01/2014
> RIP: 0010:unregister_trace_event+0x6e/0x280
> Code: 00 fc ff df 4c 89 ea 48 c1 ea 03 80 3c 02 00 0f 85 0e 02 00 00 48
> b8 00 00 00 00 00 fc ff df 4c 8b 63 08 4c 89 e2 48 c1 ea 03 <80> 3c 02
> 00 0f 85 e2 01 00 00 49 89 2c 24 48 85 ed 74 28 e8 7a 9b
> RSP: 0018:ffff88810413f370 EFLAGS: 00010a06
> RAX: dffffc0000000000 RBX: ffff888105d050b0 RCX: 0000000000000000
> RDX: 1bd5a00000000024 RSI: ffff888119e276e0 RDI: ffffffff835a8b20
> RBP: dead000000000100 R08: 0000000000000000 R09: fffffbfff0913481
> R10: ffffffff8489a407 R11: fffffbfff0913480 R12: dead000000000122
> R13: ffff888105d050b8 R14: 0000000000000000 R15: ffff888105d05028
> FS:  00007f7823e8d540(0000) GS:ffff888119e00000(0000)
> knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f7823e7ebec CR3: 000000010a058002 CR4: 0000000000330ef0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  __create_synth_event+0x1e37/0x1eb0
>  create_or_delete_synth_event+0x110/0x250
>  synth_event_run_command+0x2f/0x110
>  test_gen_synth_cmd+0x170/0x2eb [synth_event_gen_test]
>  synth_event_gen_test_init+0x76/0x9bc [synth_event_gen_test]
>  do_one_initcall+0xdb/0x480
>  do_init_module+0x1cf/0x680
>  load_module+0x6a50/0x70a0
>  __do_sys_finit_module+0x12f/0x1c0
>  do_syscall_64+0x3f/0x90
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> Fixes: 4b147936fa50 ("tracing: Add support for 'synthetic' events")
> Signed-off-by: Shang XiaoJing <shangxiaojing@huawei.com>
> Cc: stable@vger.kernel.org
> ---
>  kernel/trace/trace_events_synth.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
> index e310052dc83c..a51280a153e3 100644
> --- a/kernel/trace/trace_events_synth.c
> +++ b/kernel/trace/trace_events_synth.c
> @@ -830,6 +830,8 @@ static int register_synth_event(struct synth_event *event)
>         ret = set_synth_event_print_fmt(call);
>         if (ret < 0) {
>                 trace_remove_event_call(call);
> +               if (call->event.funcs)
> +                       return ret;
>                 goto err;
>         }
>   out:

Good catch, thanks for finding this bug!

It looks like call->event.funcs will always be true here since it's set
to &synth_event_funcs above.

So it seems like you could just call trace_remove_event_call() and fall
through for this (ret < 0) case?  If so, it might be good to put a
comment there noting that trace_remove_event_call() will call
unregister_trace_event(), so it's ok to just return.

Thanks,

Tom 

Re: [PATCH 1/2] tracing: Fix memory leak in test_gen_synth_cmd() and test_empty_synth_event()

[shangxiaojing]

On 2022/11/13 5:12, Tom Zanussi wrote:
> Hi Shang,
> 
> Thanks for finding this bug, comment below...
> 
> On Tue, 2022-11-08 at 16:31 +0800, Shang XiaoJing wrote:
>> test_gen_synth_cmd() only free buf in fail path, hence buf will leak
>> when there is no failure. Add kfree(buf) to prevent the memleak. The
>> same reason and solution in test_empty_synth_event().
>>
>> unreferenced object 0xffff8881127de000 (size 2048):
>>    comm "modprobe", pid 247, jiffies 4294972316 (age 78.756s)
>>    hex dump (first 32 bytes):
>>      20 67 65 6e 5f 73 79 6e 74 68 5f 74 65 73 74 20   gen_synth_test
>>      20 70 69 64 5f 74 20 6e 65 78 74 5f 70 69 64 5f   pid_t next_pid_
>>    backtrace:
>>      [<000000004254801a>] kmalloc_trace+0x26/0x100
>>      [<0000000039eb1cf5>] 0xffffffffa00083cd
>>      [<000000000e8c3bc8>] 0xffffffffa00086ba
>>      [<00000000c293d1ea>] do_one_initcall+0xdb/0x480
>>      [<00000000aa189e6d>] do_init_module+0x1cf/0x680
>>      [<00000000d513222b>] load_module+0x6a50/0x70a0
>>      [<000000001fd4d529>] __do_sys_finit_module+0x12f/0x1c0
>>      [<00000000b36c4c0f>] do_syscall_64+0x3f/0x90
>>      [<00000000bbf20cf3>] entry_SYSCALL_64_after_hwframe+0x63/0xcd
>> unreferenced object 0xffff8881127df000 (size 2048):
>>    comm "modprobe", pid 247, jiffies 4294972324 (age 78.728s)
>>    hex dump (first 32 bytes):
>>      20 65 6d 70 74 79 5f 73 79 6e 74 68 5f 74 65 73   empty_synth_tes
>>      74 20 20 70 69 64 5f 74 20 6e 65 78 74 5f 70 69  t  pid_t next_pi
>>    backtrace:
>>      [<000000004254801a>] kmalloc_trace+0x26/0x100
>>      [<00000000d4db9a3d>] 0xffffffffa0008071
>>      [<00000000c31354a5>] 0xffffffffa00086ce
>>      [<00000000c293d1ea>] do_one_initcall+0xdb/0x480
>>      [<00000000aa189e6d>] do_init_module+0x1cf/0x680
>>      [<00000000d513222b>] load_module+0x6a50/0x70a0
>>      [<000000001fd4d529>] __do_sys_finit_module+0x12f/0x1c0
>>      [<00000000b36c4c0f>] do_syscall_64+0x3f/0x90
>>      [<00000000bbf20cf3>] entry_SYSCALL_64_after_hwframe+0x63/0xcd
>>
>> Fixes: 9fe41efaca08 ("tracing: Add synth event generation test
>> module")
>> Signed-off-by: Shang XiaoJing <shangxiaojing@huawei.com>
>> ---
>>   kernel/trace/synth_event_gen_test.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/kernel/trace/synth_event_gen_test.c
>> b/kernel/trace/synth_event_gen_test.c
>> index 0b15e975d2c2..db1ec4809ad1 100644
>> --- a/kernel/trace/synth_event_gen_test.c
>> +++ b/kernel/trace/synth_event_gen_test.c
>> @@ -120,6 +120,7 @@ static int __init test_gen_synth_cmd(void)
>>   
>>          /* Now generate a gen_synth_test event */
>>          ret = synth_event_trace_array(gen_synth_test, vals,
>> ARRAY_SIZE(vals));
>> +       kfree(buf);
>>    out:
>>          return ret;
>>    delete:
>> @@ -227,6 +228,7 @@ static int __init test_empty_synth_event(void)
>>   
>>          /* Now trace an empty_synth_test event */
>>          ret = synth_event_trace_array(empty_synth_test, vals,
>> ARRAY_SIZE(vals));
>> +       kfree(buf);
>>    out:
>>          return ret;
>>    delete:
> 
> Makes sense, and if you do this then you could probably remove the
> other kfree() at the bottom and clean the code up a bit, like change
> this:
> 
>         /* Now generate a gen_synth_test event */
>         ret = synth_event_trace_array(gen_synth_test, vals, ARRAY_SIZE(vals));
>         kfree(buf);
>   out:
>          return ret;
>   delete:
>          /* We got an error after creating the event, delete it */
> 	synth_event_delete("gen_synth_test");
>   free:
>          kfree(buf);
> 
> 	goto out;
> }
> 
> to this:
> 
>         /* Now generate a gen_synth_test event */
>         ret = synth_event_trace_array(gen_synth_test, vals, ARRAY_SIZE(vals));
>   free:
>         kfree(buf);
>         return ret;
>   delete:
>          /* We got an error after creating the event, delete it */
> 	synth_event_delete("gen_synth_test");
>   	goto free;
> }
> 
> What do you think?
> 

Right, I thought maybe less change is better for the bugfix. It looks 
better to carry some clean up, thanks for the review, will fix in v2.

Thanks,
-- 
Shang XiaoJing

Re: [PATCH 2/2] tracing: Fix wild-memory-access in register_synth_event()

[shangxiaojing]

On 2022/11/13 5:24, Tom Zanussi wrote:
> Hi Shang,
> 
> On Tue, 2022-11-08 at 16:31 +0800, Shang XiaoJing wrote:
>> In register_synth_event(), if set_synth_event_print_fmt() failed, then
>> both trace_remove_event_call() and unregister_trace_event() will be
>> called. If call->event.funcs is not NULL, then the trace_event_call will
>> call __unregister_trace_event() twice. As the result, the second
>> __unregister_trace_event() will causes the wild-memory-access.
>>
>> register_synth_event
>>      set_synth_event_print_fmt failed
>>      trace_remove_event_call
>>          event_remove
>>              if call->event.funcs then
>>              __unregister_trace_event (first call)
>>      unregister_trace_event
>>          __unregister_trace_event (second call)
>>
>> Fix the bug by avoiding to call the second __unregister_trace_event() by
>> checking if the first one is called.
>>
>> general protection fault, probably for non-canonical address
>>          0xfbd59c0000000024: 0000 [#1] SMP KASAN PTI
>> KASAN: maybe wild-memory-access in range
>> [0xdead000000000120-0xdead000000000127]
>> CPU: 0 PID: 3807 Comm: modprobe Not tainted
>> 6.1.0-rc1-00186-g76f33a7eedb4 #299
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
>> rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org 04/01/2014
>> RIP: 0010:unregister_trace_event+0x6e/0x280
>> Code: 00 fc ff df 4c 89 ea 48 c1 ea 03 80 3c 02 00 0f 85 0e 02 00 00 48
>> b8 00 00 00 00 00 fc ff df 4c 8b 63 08 4c 89 e2 48 c1 ea 03 <80> 3c 02
>> 00 0f 85 e2 01 00 00 49 89 2c 24 48 85 ed 74 28 e8 7a 9b
>> RSP: 0018:ffff88810413f370 EFLAGS: 00010a06
>> RAX: dffffc0000000000 RBX: ffff888105d050b0 RCX: 0000000000000000
>> RDX: 1bd5a00000000024 RSI: ffff888119e276e0 RDI: ffffffff835a8b20
>> RBP: dead000000000100 R08: 0000000000000000 R09: fffffbfff0913481
>> R10: ffffffff8489a407 R11: fffffbfff0913480 R12: dead000000000122
>> R13: ffff888105d050b8 R14: 0000000000000000 R15: ffff888105d05028
>> FS:  00007f7823e8d540(0000) GS:ffff888119e00000(0000)
>> knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 00007f7823e7ebec CR3: 000000010a058002 CR4: 0000000000330ef0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> Call Trace:
>>   <TASK>
>>   __create_synth_event+0x1e37/0x1eb0
>>   create_or_delete_synth_event+0x110/0x250
>>   synth_event_run_command+0x2f/0x110
>>   test_gen_synth_cmd+0x170/0x2eb [synth_event_gen_test]
>>   synth_event_gen_test_init+0x76/0x9bc [synth_event_gen_test]
>>   do_one_initcall+0xdb/0x480
>>   do_init_module+0x1cf/0x680
>>   load_module+0x6a50/0x70a0
>>   __do_sys_finit_module+0x12f/0x1c0
>>   do_syscall_64+0x3f/0x90
>>   entry_SYSCALL_64_after_hwframe+0x63/0xcd
>>
>> Fixes: 4b147936fa50 ("tracing: Add support for 'synthetic' events")
>> Signed-off-by: Shang XiaoJing <shangxiaojing@huawei.com>
>> Cc: stable@vger.kernel.org
>> ---
>>   kernel/trace/trace_events_synth.c | 2 ++
>>   1 file changed, 2 insertions(+)
>>
>> diff --git a/kernel/trace/trace_events_synth.c b/kernel/trace/trace_events_synth.c
>> index e310052dc83c..a51280a153e3 100644
>> --- a/kernel/trace/trace_events_synth.c
>> +++ b/kernel/trace/trace_events_synth.c
>> @@ -830,6 +830,8 @@ static int register_synth_event(struct synth_event *event)
>>          ret = set_synth_event_print_fmt(call);
>>          if (ret < 0) {
>>                  trace_remove_event_call(call);
>> +               if (call->event.funcs)
>> +                       return ret;
>>                  goto err;
>>          }
>>    out:
> 
> Good catch, thanks for finding this bug!
> 
> It looks like call->event.funcs will always be true here since it's set
> to &synth_event_funcs above.
> 
> So it seems like you could just call trace_remove_event_call() and fall
> through for this (ret < 0) case?  If so, it might be good to put a
> comment there noting that trace_remove_event_call() will call
> unregister_trace_event(), so it's ok to just return.
> 

Ok, will fix in v2.

Thanks,
-- 
Shang XiaoJing