lkml.org 
[lkml]   [2012]   [Aug]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    Subject[PATCH] sched: fix divide by zero at {thread_group,task}_times
    On architectures where cputime_t is 64 bit type, is possible to trigger
    divide by zero on do_div(temp, (__force u32) total) line, if total is a
    non zero number but has lower 32 bit's zeroed. Removing casting is not
    a good solution since some do_div() implementations do cast to u32
    internally.

    This problem can be triggered in practice on very long lived processes:

    PID: 2331 TASK: ffff880472814b00 CPU: 2 COMMAND: "oraagent.bin"
    #0 [ffff880472a51b70] machine_kexec at ffffffff8103214b
    #1 [ffff880472a51bd0] crash_kexec at ffffffff810b91c2
    #2 [ffff880472a51ca0] oops_end at ffffffff814f0b00
    #3 [ffff880472a51cd0] die at ffffffff8100f26b
    #4 [ffff880472a51d00] do_trap at ffffffff814f03f4
    #5 [ffff880472a51d60] do_divide_error at ffffffff8100cfff
    #6 [ffff880472a51e00] divide_error at ffffffff8100be7b
    [exception RIP: thread_group_times+0x56]
    RIP: ffffffff81056a16 RSP: ffff880472a51eb8 RFLAGS: 00010046
    RAX: bc3572c9fe12d194 RBX: ffff880874150800 RCX: 0000000110266fad
    RDX: 0000000000000000 RSI: ffff880472a51eb8 RDI: 001038ae7d9633dc
    RBP: ffff880472a51ef8 R8: 00000000b10a3a64 R9: ffff880874150800
    R10: 00007fcba27ab680 R11: 0000000000000202 R12: ffff880472a51f08
    R13: ffff880472a51f10 R14: 0000000000000000 R15: 0000000000000007
    ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
    #7 [ffff880472a51f00] do_sys_times at ffffffff8108845d
    #8 [ffff880472a51f40] sys_times at ffffffff81088524
    #9 [ffff880472a51f80] system_call_fastpath at ffffffff8100b0f2
    RIP: 0000003808caac3a RSP: 00007fcba27ab6d8 RFLAGS: 00000202
    RAX: 0000000000000064 RBX: ffffffff8100b0f2 RCX: 0000000000000000
    RDX: 00007fcba27ab6e0 RSI: 000000000076d58e RDI: 00007fcba27ab6e0
    RBP: 00007fcba27ab700 R8: 0000000000000020 R9: 000000000000091b
    R10: 00007fcba27ab680 R11: 0000000000000202 R12: 00007fff9ca41940
    R13: 0000000000000000 R14: 00007fcba27ac9c0 R15: 00007fff9ca41940
    ORIG_RAX: 0000000000000064 CS: 0033 SS: 002b

    Cc: stable@vger.kernel.org
    Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
    ---
    kernel/sched/core.c | 34 ++++++++++++++++++++--------------
    1 files changed, 20 insertions(+), 14 deletions(-)

    diff --git a/kernel/sched/core.c b/kernel/sched/core.c
    index 468bdd4..1d441b0 100644
    --- a/kernel/sched/core.c
    +++ b/kernel/sched/core.c
    @@ -3142,6 +3142,20 @@ void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *st)
    # define nsecs_to_cputime(__nsecs) nsecs_to_jiffies(__nsecs)
    #endif

    +static cputime_t scale_utime(cputime_t utime, cputime_t rtime, cputime_t total)
    +{
    + u64 temp = (__force u64) rtime;
    +
    + temp *= (__force u64) utime;
    +
    + if (sizeof(cputime_t) == 4)
    + do_div(temp, (__force u32) total);
    + else
    + temp = div64_u64(temp, (__force u64) total);
    +
    + return (__force cputime_t) temp;
    +}
    +
    void task_times(struct task_struct *p, cputime_t *ut, cputime_t *st)
    {
    cputime_t rtime, utime = p->utime, total = utime + p->stime;
    @@ -3151,13 +3165,9 @@ void task_times(struct task_struct *p, cputime_t *ut, cputime_t *st)
    */
    rtime = nsecs_to_cputime(p->se.sum_exec_runtime);

    - if (total) {
    - u64 temp = (__force u64) rtime;
    -
    - temp *= (__force u64) utime;
    - do_div(temp, (__force u32) total);
    - utime = (__force cputime_t) temp;
    - } else
    + if (total)
    + utime = scale_utime(utime, rtime, total);
    + else
    utime = rtime;

    /*
    @@ -3184,13 +3194,9 @@ void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *st)
    total = cputime.utime + cputime.stime;
    rtime = nsecs_to_cputime(cputime.sum_exec_runtime);

    - if (total) {
    - u64 temp = (__force u64) rtime;
    -
    - temp *= (__force u64) cputime.utime;
    - do_div(temp, (__force u32) total);
    - utime = (__force cputime_t) temp;
    - } else
    + if (total)
    + utime = scale_utime(cputime.utime, rtime, total);
    + else
    utime = rtime;

    sig->prev_utime = max(sig->prev_utime, utime);
    --
    1.7.1


    \
     
     \ /
      Last update: 2012-08-08 12:03    [W:0.024 / U:32.324 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site