linux-kernel - Re: [PATCH v2 ] devcoredump : Serialize devcd

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Message-ID: <13df1664-fc52-4772-afa1-4f75019b7830@quicinc.com>
Date:   Tue, 26 Apr 2022 19:34:07 +0530
From:   Mukesh Ojha <quic_mojha@...cinc.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Johannes Berg <johannes@...solutions.net>,
        <linux-kernel@...r.kernel.org>
CC:     <sboyd@...nel.org>, <rafael@...nel.org>,
        <gregkh@...uxfoundation.org>, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH v2 ] devcoredump : Serialize devcd_del work



On 4/26/2022 1:07 AM, Thomas Gleixner wrote:
> Cc+: Kees
> 
> On Mon, Apr 25 2022 at 19:19, Johannes Berg wrote:
>> On Mon, 2022-04-25 at 19:00 +0200, Thomas Gleixner wrote:
>>>
>>> Johannes, can you please explain whether this immediate flush in
>>> disabled_store() is really required and if so, why?
>>>
>> I don't really know, as I remember that requirement (or maybe even code,
>> not sure) came from Kees, who needed the lockdown.
>>
>> Given the use case (ChromeOS?) I'm not sure I see a need to flush all of
>> them, since I guess a typical system would set the lockdown early in
>> boot and hopefully not have a crash-dump around already.
>>
>> That said, I don't think the diagram you made works - fn() during the
>> iteration is guaranteed to be invoked with a reference of its own, so
>> the put_device() there can't be the last reference, only as fn() returns
>> you'd put the last reference *there*, freeing it.
> 
> Bah, you are right, it's magically protected by the klist ref, which
> prevents devcd from going away. Damned obvious.
> 
> This really needs comments why this all can magically "work".
> 
> Thanks,
> 
>          tglx
> 

Thanks you all for your time in reviewing this.
I tried to address few comments in v3 here.

https://lore.kernel.org/lkml/1650981343-11739-1-git-send-email-quic_mojha@quicinc.com/

While, we would like to hear from Kees about reason of immediate flush 
from disabled_store().

Regards,
-Mukesh
> 
> 
>