linux-kernel - Re: [PATCH v1 1/1] scsi: ufs: Add command logging infrastructure

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Message-ID: <20191029054620.GG1929@tuxbook-pro>
Date:   Mon, 28 Oct 2019 22:46:20 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     cang@...eaurora.org
Cc:     Avri Altman <Avri.Altman@....com>,
        "Winkler, Tomas" <tomas.winkler@...el.com>,
        asutoshd@...eaurora.org, nguyenb@...eaurora.org,
        rnayak@...eaurora.org, linux-scsi@...r.kernel.org,
        kernel-team@...roid.com, saravanak@...gle.com, salyzyn@...gle.com,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Pedro Sousa <pedrom.sousa@...opsys.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Evan Green <evgreen@...omium.org>,
        Janek Kotas <jank@...ence.com>,
        Stanley Chu <stanley.chu@...iatek.com>,
        Bean Huo <beanhuo@...ron.com>,
        Subhash Jadavani <subhashj@...eaurora.org>,
        Arnd Bergmann <arnd@...db.de>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 1/1] scsi: ufs: Add command logging infrastructure

On Mon 28 Oct 19:37 PDT 2019, cang@...eaurora.org wrote:

> On 2019-10-23 18:33, Avri Altman wrote:
> > > 
> > > > Add the necessary infrastructure to keep timestamp history of
> > > > commands, events and other useful info for debugging complex issues.
> > > > This helps in diagnosing events leading upto failure.
> > > 
> > > Why not use tracepoints, for that?
> > Ack on Tomas's comment.
> > Are there any pieces of information that you need not provided by the
> > upiu tracer?
> > 
> > Thanks,
> > Avri
> 
> In extreme cases, when the UFS runs into bad state, system may crash. There
> may not be a chance to collect trace. If trace is not collected and failure
> is hard to be reproduced, some command logs prints would be very helpful to
> help understand what was going on before we run into failure.
> 

This is a common problem shared among many/all subsystems, so it's
better to rely on a generic solution for this; such as using tracepoints
dumped into pstore/ramoops.

Regards,
Bjorn