lkml.org 
[lkml]   [2009]   [Mar]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH] Fix fixpoint divide exception in acct_update_integrals
From: Heiko Carstens <heiko.carstens@de.ibm.com>

Frans Pop reported the crash below when running an s390 kernel under Hercules:

17180168.889947! Kernel BUG at 000738b4 verbose debug info unavailable!
17180168.890213! fixpoint divide exception: 0009 #1! SMP
17180168.890487! 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
17180168.891891! CPU: 0 Not tainted 2.6.27.19 #13
17180168.892116! Process awk (pid: 2069, task: 0f9ed9b8, ksp: 0f4f7d18)
17180168.892371! Krnl PSW : 070c1000 800738b4 (acct_update_integrals+0x4c/0x118)
17180168.892830! R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:0 CC:1 PM:0
17180168.893115! Krnl GPRS: 00000000 000007d0 7fffffff fffff830
17180168.893376! 00000000 ffffffff 00000002 0f9ed9b8
17180168.893621! 00000000 00008ca0 00000000 0f9ed9b8
17180168.893873! 0f9edda4 8007386e 0f4f7ec8 0f4f7e98
17180168.894881! Krnl Code: 800738aa: a71807d0 lhi %r1,2000
17180168.895245! 800738ae: 8c200001 srdl %r2,1
17180168.895563! 800738b2: 1d21 dr %r2,%r1
17180168.895936! >800738b4: 5810d10e l %r1,270(%r13)
17180168.896246! 800738b8: 1823 lr %r2,%r3
17180168.896598! 800738ba: 4130f060 la %r3,96(%r15)
17180168.896913! 800738be: 0de1 basr %r14,%r1
17180168.897283! 800738c0: 5800f060 l %r0,96(%r15)
17180168.897517! Call Trace:
17180168.897656! ( <000000000004fdea>! blocking_notifier_call_chain+0x1e/0x2c)
17180168.897987! <0000000000038502>! do_exit+0x106/0x7c0
17180168.898275! <0000000000038c36>! do_group_exit+0x7a/0xb4
17180168.898570! <0000000000038c8e>! SyS_exit_group+0x1e/0x30
17180168.898869! <0000000000021c28>! sysc_do_restart+0x12/0x16
17180168.899173! <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>
---
kernel/tsacct.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

Index: linux-2.6/kernel/tsacct.c
===================================================================
--- linux-2.6.orig/kernel/tsacct.c
+++ linux-2.6/kernel/tsacct.c
@@ -122,8 +122,10 @@ void acct_update_integrals(struct task_s
if (likely(tsk->mm)) {
cputime_t time, dtime;
struct timeval value;
+ unsigned long flags;
u64 delta;

+ local_irq_save(flags);
time = tsk->stime + tsk->utime;
dtime = cputime_sub(time, tsk->acct_timexpd);
jiffies_to_timeval(cputime_to_jiffies(dtime), &value);
@@ -131,10 +133,12 @@ void acct_update_integrals(struct task_s
delta = delta * USEC_PER_SEC + value.tv_usec;

if (delta == 0)
- return;
+ goto out;
tsk->acct_timexpd = time;
tsk->acct_rss_mem1 += delta * get_mm_rss(tsk->mm);
tsk->acct_vm_mem1 += delta * tsk->mm->total_vm;
+ out:
+ local_irq_restore(flags);
}
}


\
 
 \ /
  Last update: 2009-03-09 13:35    [W:0.035 / U:23.136 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site