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Date:   Mon, 18 May 2020 17:18:01 +0000
From:   Luis Chamberlain <mcgrof@kernel.org>
To:     Ben Greear <greearb@candelatech.com>
Cc:     Johannes Berg <johannes@sipsolutions.net>, jeyu@kernel.org,
        akpm@linux-foundation.org, arnd@arndb.de, rostedt@goodmis.org,
        mingo@redhat.com, aquini@redhat.com, cai@lca.pw, dyoung@redhat.com,
        bhe@redhat.com, peterz@infradead.org, tglx@linutronix.de,
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        schlad@suse.de, andriy.shevchenko@linux.intel.com,
        keescook@chromium.org, daniel.vetter@ffwll.ch, will@kernel.org,
        mchehab+samsung@kernel.org, kvalo@codeaurora.org,
        davem@davemloft.net, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-wireless@vger.kernel.org,
        ath10k@lists.infradead.org
Subject: Re: [PATCH v2 12/15] ath10k: use new module_firmware_crashed()
Message-ID: <20200518171801.GL11244@42.do-not-panic.com>
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On Mon, May 18, 2020 at 10:15:45AM -0700, Ben Greear wrote:
> 
> 
> On 05/18/2020 10:09 AM, Luis Chamberlain wrote:
> > On Mon, May 18, 2020 at 09:58:53AM -0700, Ben Greear wrote:
> > > 
> > > 
> > > On 05/18/2020 09:51 AM, Luis Chamberlain wrote:
> > > > On Sat, May 16, 2020 at 03:24:01PM +0200, Johannes Berg wrote:
> > > > > On Fri, 2020-05-15 at 21:28 +0000, Luis Chamberlain wrote:> module_firmware_crashed
> > > > > 
> > > > > You didn't CC me or the wireless list on the rest of the patches, so I'm
> > > > > replying to a random one, but ...
> > > > > 
> > > > > What is the point here?
> > > > > 
> > > > > This should in no way affect the integrity of the system/kernel, for
> > > > > most devices anyway.
> > > > 
> > > > Keyword you used here is "most device". And in the worst case, *who*
> > > > knows what other odd things may happen afterwards.
> > > > 
> > > > > So what if ath10k's firmware crashes? If there's a driver bug it will
> > > > > not handle it right (and probably crash, WARN_ON, or something else),
> > > > > but if the driver is working right then that will not affect the kernel
> > > > > at all.
> > > > 
> > > > Sometimes the device can go into a state which requires driver removal
> > > > and addition to get things back up.
> > > 
> > > It would be lovely to be able to detect this case in the driver/system
> > > somehow!  I haven't seen any such cases recently,
> > 
> > I assure you that I have run into it. Once it does again I'll report
> > the crash, but the problem with some of this is that unless you scrape
> > the log you won't know. Eventually, a uevent would indeed tell inform
> > me.
> > 
> > > but in case there is
> > > some common case you see, maybe we can think of a way to detect it?
> > 
> > ath10k is just one case, this patch series addresses a simple way to
> > annotate this tree-wide.
> > 
> > > > > So maybe I can understand that maybe you want an easy way to discover -
> > > > > per device - that the firmware crashed, but that still doesn't warrant a
> > > > > complete kernel taint.
> > > > 
> > > > That is one reason, another is that a taint helps support cases *fast*
> > > > easily detect if the issue was a firmware crash, instead of scraping
> > > > logs for driver specific ways to say the firmware has crashed.
> > > 
> > > You can listen for udev events (I think that is the right term),
> > > and find crashes that way.  You get the actual crash info as well.
> > 
> > My follow up to this was to add uevent to add_taint() as well, this way
> > these could generically be processed by userspace.
> 
> I'm not opposed to the taint, though I have not thought much on it.
> 
> But, if you can already get the crash info from uevent, and it automatically
> comes without polling or scraping logs, then what benefit beyond that does
> the taint give you?

From a support perspective it is a *crystal* clear sign that the device
and / or device driver may be in a very bad state, in a generic way.

  Luis