1. 09 Mar, 2009 1 commit
    • Heiko Carstens's avatar
      Fix fixpoint divide exception in acct_update_integrals · 6d5b5acc
      Heiko Carstens authored
      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: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      6d5b5acc
  2. 08 Mar, 2009 18 commits
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  4. 05 Mar, 2009 15 commits