Date: Tue, 12 Aug 1997 18:10:50 -0700 (PDT) From: Julian Elischer <julian@FreeBSD.ORG> To: hackers@FreeBSD.ORG Subject: 2.2.2+ crash.. more info Message-ID: <199708130110.SAA21060@freefall.freebsd.org>
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We have several hundred Bsd machines here.. we see this one enough for
me to recognise it..
the plot thickens..
I have discovered the following:
1/ the code that crashes:
scanning the queues in swithc:
looking a the queue array:
}, {
ph_link = 0xf01be350,
ph_rlink = 0xf01be350
}, {
ph_link = 0x0, <----- a few instructions before, this ALSO was 0xf07e1000
ph_rlink = 0xf07e1000
}, {
ph_link = 0xf01be360,
ph_rlink = 0xf01be360
}, {
ph_link = 0xf01be368,
ph_rlink = 0xf01be368
},
one entry is bogus from the registers we see it was 0xf07e1000
shortly before.
looking at the registers we can see what proc struct is being looked at..
$11 = {
p_procq = {
tqe_next = 0x0,
tqe_prev = 0xf01be7e8
},
p_list = {
le_next = 0xf07e1200,
le_prev = 0xf07d2808
},
...
this is where the NULL came from
but wait!
this looks like an entry in a sleep queue..
sure enough!
in the array of sleep queues...
}, {
tqh_first = 0x0,
tqh_last = 0xf01be7d8
}, {
tqh_first = 0x0,
tqh_last = 0xf01be7e0
}, {
tqh_first = 0xf07e1000, <--------- !!!!!
tqh_last = 0xf07e1000
}, {
tqh_first = 0x0,
tqh_last = 0xf01be7f0
}, {
tqh_first = 0x0,
so why was this sleeping?
looking in the proc struct again..
p_wchan = 0xf272f698,
p_wmesg = 0xf015bead "swread",
Since the processes proc structure looks liek a sleeping process,
it was probably put onto the sleep queue last, when it was already on
the runnable queue.
how can this happen?
some ideas:
it was half way through being woken up when the scheduling occured?
and still looked like a sleeping process? unlikely..
it was put onto the sleep queue accidentally by interrupt code
that just had it's proc address by accident?
unlikely.
somehow a wakeup occured during the tsleep call?
sounds unlikely..
code examinations will follow with more info..
if this strikes anyone as familiar, do chime in!
julian
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