linux-kernel - Re: [BUG][bisected 270065e] linux-next fails to boot on powerpc

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Message-ID: <1503094414.2622.21.camel@wdc.com>
Date:   Fri, 18 Aug 2017 22:13:36 +0000
From:   Bart Van Assche <Bart.VanAssche@....com>
To:     "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "abdhalee@...ux.vnet.ibm.com" <abdhalee@...ux.vnet.ibm.com>,
        "brking@...ux.vnet.ibm.com" <brking@...ux.vnet.ibm.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "hch@....de" <hch@....de>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "sfr@...b.auug.org.au" <sfr@...b.auug.org.au>,
        "sachinp@...ux.vnet.ibm.com" <sachinp@...ux.vnet.ibm.com>,
        "linux-next@...r.kernel.org" <linux-next@...r.kernel.org>,
        "hare@...e.com" <hare@...e.com>,
        "mpe@...erman.id.au" <mpe@...erman.id.au>
Subject: Re: [BUG][bisected 270065e] linux-next fails to boot on powerpc

On Fri, 2017-08-18 at 16:57 -0500, Brian King wrote:
> To add to my analysis above, #9 should not be there... It looks like
> jiffies_at_alloc would also be getting reinitialized in this case, resulting in
> a perpetual retry, which is what I was seeing.

Hello Brian,

Some time ago I noticed that jiffies_at_alloc is indeed set while a command
is being prepared instead of at command allocation time. I think that
behavior was introduced in 2005 through commit b21a41385118 ("[SCSI] add
global timeout to the scsi mid-layer"). At that time SCSI commands were
allocated at prep time and freed at unprep time. Recently that has been
changed such that a SCSI command (struct scsi_cmnd) has the same lifetime as
struct request. In other words, it was not possible in 2005 but it is
possible today to set jiffies_at_alloc at command allocation time instead of
when a command is being prepared. Do you want me to submit a patch that
implements this change?

Bart.