Date: Tue, 20 Sep 2005 00:20:21 GMT From: "Andrew Watkins" <awatkins@ejungle.us> To: freebsd-i386@FreeBSD.org Subject: Re: i386/78929: atapicam prevents boot, system hangs Message-ID: <200509200020.j8K0KLj1031884@freefall.freebsd.org>
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The following reply was made to PR i386/78929; it has been noted by GNATS.
From: "Andrew Watkins" <awatkins@ejungle.us>
To: <bug-followup@FreeBSD.org>,
<harrycoin@quietfountain.com>
Cc:
Subject: Re: i386/78929: atapicam prevents boot, system hangs
Date: Mon, 19 Sep 2005 17:19:08 -0700
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This happened on both i386 for me and amd64 with 5.4, both using SMP and not
for dual processor support (dell sc1425) with a QSI-DVD burner. Dump of the
kernel provided this:
_mtx_lock_sleep+0x77 (kern_mutex.c, 521)
Get_softc+0x80 (atapi-cam.c, 776)
Atapi_cam_reinit_bus+0x16 (atapi-cam.c, 195)
I read through the code to see where the mutex is initialized and found that
the only place it is done is atapi_cam_attach_bus. I guess its possible for
the code to reach the atapi_cam_reinit_bus which calls get_softc before the
bus is attached? Anyway, I changed get_softc to look to see if the mutex is
initialized before locking and that did the trick. Below is my modified
code:
static struct atapi_xpt_softc *
get_softc(struct ata_channel *ata_ch) {
struct atapi_xpt_softc *scp = NULL;
/* There could be a race condition where the atapi mtx has not been
initialized */
if (mtx_initialized(&atapicam_softc_mtx) == 0)
mtx_init(&atapicam_softc_mtx, "ATAPI/CAM softc mutex", NULL,
MTX_DEF);
mtx_lock(&atapicam_softc_mtx);
LIST_FOREACH(scp, &all_buses, chain) {
if (scp->ata_ch == ata_ch)
break;
}
mtx_unlock(&atapicam_softc_mtx);
return scp;
}
After that it booted no problem and burned a DVD like a champ.
I don't think this change can impact the rest of the system, but can someone
let me know as this is going to be a production box. Let me know if you
need anymore information as I have trace and the kernel.debug (burned on a
dvd as my trophy).
Andrew
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<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>This happened on both i386 for me and amd64 with 5.4, =
both
using SMP and not for dual processor support (dell sc1425) with a =
QSI-DVD
burner. Dump of the kernel provided =
this:<o:p></o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>_<i><span =
style=3D'font-style:italic'>mtx</span></i>_lock_sleep+0x77
(kern_mutex.c, 521)<o:p></o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>Get_softc+0x80 (atapi-cam.c, =
776)<o:p></o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>Atapi_cam_reinit_bus+0x16 (atapi-cam.c, =
195)<o:p></o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>I read through the code to see where the mutex is
initialized and found that the only place it is done is =
atapi_cam_attach_bus.
I guess its possible for the code to reach the atapi_cam_reinit_bus =
which calls
get_softc before the bus is attached? Anyway, I changed get_softc =
to look
to see if the mutex is initialized before locking and that did the =
trick.
Below is my modified code:<o:p></o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>static struct atapi_xpt_softc =
*<o:p></o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>get_softc(struct ata_channel *ata_ch) =
{<o:p></o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'> struct atapi_xpt_softc *scp =3D =
NULL;<o:p></o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'> /* There could be a race condition =
where
the atapi mtx has not been initialized */<o:p></o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'> if
(mtx_initialized(&atapicam_softc_mtx) =3D=3D =
0)<o:p></o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>
mtx_init(&atapicam_softc_mtx, "ATAPI/CAM softc mutex", =
NULL,
MTX_DEF);<o:p></o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'> =
mtx_lock(&atapicam_softc_mtx);<o:p></o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'> LIST_FOREACH(scp, &all_buses, =
chain)
{<o:p></o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'> =
if
(scp->ata_ch =3D=3D ata_ch)<o:p></o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'> =
break;<o:p></o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'> }<o:p></o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'> =
mtx_unlock(&atapicam_softc_mtx);<o:p></o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'> return =
scp;<o:p></o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>}<o:p></o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>After that it booted no problem and burned a DVD like =
a
champ.<o:p></o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>I don’t think this change can impact the rest =
of the
system, but can someone let me know as this is going to be a production =
box.
Let me know if you need anymore information as I have trace and the
kernel.debug (burned on a dvd as my =
trophy).<o:p></o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=3DMsoNormal><font size=3D2 face=3DArial><span =
style=3D'font-size:10.0pt;
font-family:Arial'>Andrew<o:p></o:p></span></font></p>
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