linux-kernel - Re: [PATCH] devcoredump: increase the device delete timeout to 10 mins

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Date:   Tue, 08 Feb 2022 22:54:34 +0100
From:   Johannes Berg <johannes@...solutions.net>
To:     Abhinav Kumar <quic_abhinavk@...cinc.com>,
        linux-kernel@...r.kernel.org
Cc:     rafael@...nel.org, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, swboyd@...omium.org,
        khsieh@...eaurora.org, nganji@...eaurora.org,
        seanpaul@...omium.org, gregkh@...uxfoundation.org,
        dmitry.baryshkov@...aro.org, aravindh@...eaurora.org,
        freedreno@...ts.freedesktop.org
Subject: Re: [PATCH] devcoredump: increase the device delete timeout to 10
 mins

On Tue, 2022-02-08 at 13:40 -0800, Abhinav Kumar wrote:
> > 
> I am checking what usermode sees and will get back ( I didnt see an 
> error do most likely it was EOF ). I didnt follow the second part.

I think probably it got -ENODEV, looking at kernfs_file_read_iter().

> If the file descriptor read returns EOF, even if we consider them 
> separate how will it resolve this issue?
> 
> My earlier questions were related to fixing it in devcoredump to detect
> and fix it there. Are you suggesting to fix in usermode instead? How?
> 

Yeah, no, you cannot fix it in userspace.

But I just followed the rabbit hole down kernfs and all, and it looks
like indeed the read would be cut short with -ENODEV, sorry.

It doesn't look like there's good API for this, but it seems at least
from the underlying kernfs POV it should be possible to get_device() in
open and put_device() in release, so that the device sticks around while
somebody has the file open? It's entirely virtual, so this should be OK?

johannes