Frans Pop reported the crash below when running an s390 kernel under Hercules:
Kernel BUG at 000738b4 verbose debug info unavailable!
fixpoint divide exception: 0009 #1! SMP
Modules linked in: nfs lockd nfs_acl sunrpc ctcm fsm tape_34xx
cu3088 tape ccwgroup tape_class ext3 jbd mbcache dm_mirror dm_log dm_snapshot
dm_mod dasd_eckd_mod dasd_mod
CPU: 0 Not tainted 2.6.27.19 #13
Process awk (pid: 2069, task: 0f9ed9b8, ksp: 0f4f7d18)
Krnl PSW : 070c1000 800738b4 (acct_update_integrals+0x4c/0x118)
R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:0 CC:1 PM:0
Krnl GPRS: 00000000 000007d0 7fffffff fffff830
00000000 ffffffff 00000002 0f9ed9b8
00000000 00008ca0 00000000 0f9ed9b8
0f9edda4 8007386e 0f4f7ec8 0f4f7e98
Krnl Code: 800738aa: a71807d0 lhi %r1,2000
800738ae: 8c200001 srdl %r2,1
800738b2: 1d21 dr %r2,%r1
>800738b4: 5810d10e l %r1,270(%r13)
800738b8: 1823 lr %r2,%r3
800738ba: 4130f060 la %r3,96(%r15)
800738be: 0de1 basr %r14,%r1
800738c0: 5800f060 l %r0,96(%r15)
Call Trace:
( <000000000004fdea>! blocking_notifier_call_chain+0x1e/0x2c)
<0000000000038502>! do_exit+0x106/0x7c0
<0000000000038c36>! do_group_exit+0x7a/0xb4
<0000000000038c8e>! SyS_exit_group+0x1e/0x30
<0000000000021c28>! sysc_do_restart+0x12/0x16
<0000000077e7e924>! 0x77e7e924
Reason for this is that cpu time accounting usually only happens from
interrupt context, but acct_update_integrals gets also called from
process context with interrupts enabled.
So in acct_update_integrals we may end up with the following scenario:
Between reading tsk->stime/tsk->utime and tsk->acct_timexpd an interrupt
happens which updates accouting values. This causes acct_timexpd to be
greater than the former stime + utime. The subsequent calculation of
dtime = cputime_sub(time, tsk->acct_timexpd);
will be negative and the division performed by
cputime_to_jiffies(dtime)
will generate an exception since the result won't fit into a 32 bit
register.
In order to fix this just always disable interrupts while accessing any
of the accounting values.
Reported by: Frans Pop <elendil@planet.nl>
Tested by: Frans Pop <elendil@planet.nl>
Cc: stable@kernel.org
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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