From: "Prekas, George" <prekageo@amazon.com>
To: Jan Kiszka <jan.kiszka@siemens.com>, <linux-kernel@vger.kernel.org>
Cc: Kieran Bingham <kbingham@kernel.org>
Subject: Re: [PATCH] scripts/gdb: fix list_for_each
Date: Tue, 22 Sep 2020 12:17:00 -0500 [thread overview]
Message-ID: <109fe98d-4143-cfd3-b145-8d5fee189f63@amazon.com> (raw)
In-Reply-To: <2516a051-306f-670b-1f9e-d46fc577c7f8@siemens.com>
On 9/22/2020 9:32 AM, Jan Kiszka wrote:
>
> On 22.09.20 16:28, George Prekas wrote:
>> If the next pointer is NULL, list_for_each gets stuck in an infinite
>> loop.
>>
>> Signed-off-by: George Prekas <prekageo@amazon.com>
>> ---
>> scripts/gdb/linux/lists.py | 2 ++
>> 1 file changed, 2 insertions(+)
>>
>> diff --git a/scripts/gdb/linux/lists.py b/scripts/gdb/linux/lists.py
>> index c487ddf09d38..424a91c1aa8b 100644
>> --- a/scripts/gdb/linux/lists.py
>> +++ b/scripts/gdb/linux/lists.py
>> @@ -27,6 +27,8 @@ def list_for_each(head):
>> raise TypeError("Must be struct list_head not {}"
>> .format(head.type))
>>
>> + if head['next'] == 0:
>> + return
>> node = head['next'].dereference()
>> while node.address != head.address:
>> yield node.address
>
> Obviously, infinite loops are bad and should be avoided. But NULL is
> bug, isn't it? Shouldn't we report such a corruption?
>
Hi Jan,
Is it a bug? Or does it mean that the list is empty?
Let me give some background. If you do the following:
$ qemu-system-x86_64 -nographic -m 1024 -kernel
build/arch/x86/boot/bzImage -s -S < /dev/null > /dev/null &
$ gdb -q build/vmlinux -ex 'target remote localhost:1234' -iex 'set
auto-load safe-path /' -ex 'lx-symbols'
You will see:
loading vmlinux
scanning for modules in /home/ubuntu/linux-5.8.10
no module object found for ''
And the last line repeats forever. This happens because modules.next ==
NULL. This is the Python stack trace:
File ".../symbols.py", line 174, in invoke
self.load_all_symbols()
File ".../symbols.py", line 161, in load_all_symbols
[self.load_module_symbols(module) for module in module_list]
File ".../symbols.py", line 161, in <listcomp>
[self.load_module_symbols(module) for module in module_list]
File ".../modules.py", line 30, in module_list
for module in lists.list_for_each_entry(modules, module_ptr_type,
"list"):
File ".../lists.py", line 41, in list_for_each_entry
for node in list_for_each(head):
File ".../lists.py", line 31, in list_for_each
traceback.print_stack()
This patch tries to fix the above problem.
George
next prev parent reply other threads:[~2020-09-22 17:17 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-22 14:28 [PATCH] scripts/gdb: fix list_for_each George Prekas
2020-09-22 14:32 ` Jan Kiszka
2020-09-22 17:17 ` Prekas, George [this message]
2020-09-22 19:11 ` Kieran Bingham
2020-09-23 13:13 ` George Prekas
2020-09-23 21:17 ` Kieran Bingham
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