linux-kernel - Re: [PATCH] workqueue: Try to catch flush_work() without INIT

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Message-ID: <90c831b3-0d09-3cf7-5a2c-2fa7afaa003e@i-love.sakura.ne.jp>
Date:   Sat, 19 Jan 2019 11:41:22 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Daniel Jordan <daniel.m.jordan@...cle.com>
Cc:     Tejun Heo <tj@...nel.org>, Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] workqueue: Try to catch flush_work() without INIT_WORK().

On 2019/01/19 4:48, Daniel Jordan wrote:
> On Sat, Jan 19, 2019 at 02:04:58AM +0900, Tetsuo Handa wrote:
>> syzbot found a flush_work() caller who forgot to call INIT_WORK()
>> because that work_struct was allocated by kzalloc(). But the message
>>
>>   INFO: trying to register non-static key.
>>   the code is fine but needs lockdep annotation.
>>   turning off the locking correctness validator.
>>
>> by lock_map_acquire() is failing to tell that INIT_WORK() is missing.
>>
>> Since flush_work() without INIT_WORK() is a bug, and INIT_WORK() should
>> set ->func field to non-zero, let's warn if ->func field is zero.
> 
> Agree that it's a good idea to catch this.  So the caller did flush_work
> without queueing it beforehand?  Out of curiosity, what situation leads to
> this?  Link to the report might be helpful.

I quoted the patch below.

> 
>> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
>> index 392be4b..a503ad9 100644
>> --- a/kernel/workqueue.c
>> +++ b/kernel/workqueue.c
>> @@ -2908,6 +2908,9 @@ static bool __flush_work(struct work_struct *work, bool from_cancel)
>>  	if (WARN_ON(!wq_online))
>>  		return false;
>>  
>> +	if (WARN_ON(!work->func))
>> +		return false;
>> +
> 
> __queue_work has a sanity check already for work, but using list_empty.  Seems
> slightly better to be consistent?
> 

list_empty() won't work, for "struct work_struct" is embedded into a struct
which is allocated by kzalloc().



>From 1bbf8d9c7aaef78d7f483d2131261162485c6f72 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
Date: Sat, 19 Jan 2019 01:38:53 +0900
Subject: [PATCH] drm/vkms: Fix flush_work() without INIT_WORK().

syzbot is hitting a lockdep warning [1] because flush_work() is called
without INIT_WORK() after kzalloc() at vkms_atomic_crtc_reset().

Commit 6c234fe37c57627a ("drm/vkms: Implement CRC debugfs API") added
INIT_WORK() to only vkms_atomic_crtc_duplicate_state() side. Assuming
that lifecycle of crc_work is appropriately managed, fix this problem
by adding INIT_WORK() to vkms_atomic_crtc_reset() side.

[1] https://syzkaller.appspot.com/bug?id=a5954455fcfa51c29ca2ab55b203076337e1c770

Reported-and-tested-by: syzbot <syzbot+12f1b031b6da017e34f8@...kaller.appspotmail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
---
 drivers/gpu/drm/vkms/vkms_crtc.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/gpu/drm/vkms/vkms_crtc.c b/drivers/gpu/drm/vkms/vkms_crtc.c
index 177bbcb..3c37d8c 100644
--- a/drivers/gpu/drm/vkms/vkms_crtc.c
+++ b/drivers/gpu/drm/vkms/vkms_crtc.c
@@ -104,6 +104,7 @@ static void vkms_atomic_crtc_reset(struct drm_crtc *crtc)
 	vkms_state = kzalloc(sizeof(*vkms_state), GFP_KERNEL);
 	if (!vkms_state)
 		return;
+	INIT_WORK(&vkms_state->crc_work, vkms_crc_work_handle);
 
 	crtc->state = &vkms_state->base;
 	crtc->state->crtc = crtc;
-- 
1.8.3.1