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    Subject[021/118] hrtimer: Add expiry time overflow check in hrtimer_interrupt
    3.2.45-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Prarit Bhargava <prarit@redhat.com>

    commit 8f294b5a139ee4b75e890ad5b443c93d1e558a8b upstream.

    The settimeofday01 test in the LTP testsuite effectively does

    gettimeofday(current time);
    settimeofday(Jan 1, 1970 + 100 seconds);
    settimeofday(current time);

    This test causes a stack trace to be displayed on the console during the
    setting of timeofday to Jan 1, 1970 + 100 seconds:

    [ 131.066751] ------------[ cut here ]------------
    [ 131.096448] WARNING: at kernel/time/clockevents.c:209 clockevents_program_event+0x135/0x140()
    [ 131.104935] Hardware name: Dinar
    [ 131.108150] Modules linked in: sg nfsv3 nfs_acl nfsv4 auth_rpcgss nfs dns_resolver fscache lockd sunrpc nf_conntrack_netbios_ns nf_conntrack_broadcast ipt_MASQUERADE ip6table_mangle ip6t_REJECT nf_conntrack_ipv6 nf_defrag_ipv6 iptable_nat nf_nat_ipv4 nf_nat iptable_mangle ipt_REJECT nf_conntrack_ipv4 nf_defrag_ipv4 xt_conntrack nf_conntrack ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter ip_tables kvm_amd kvm sp5100_tco bnx2 i2c_piix4 crc32c_intel k10temp fam15h_power ghash_clmulni_intel amd64_edac_mod pcspkr serio_raw edac_mce_amd edac_core microcode xfs libcrc32c sr_mod sd_mod cdrom ata_generic crc_t10dif pata_acpi radeon i2c_algo_bit drm_kms_helper ttm drm ahci pata_atiixp libahci libata usb_storage i2c_core dm_mirror dm_region_hash dm_log dm_mod
    [ 131.176784] Pid: 0, comm: swapper/28 Not tainted 3.8.0+ #6
    [ 131.182248] Call Trace:
    [ 131.184684] <IRQ> [<ffffffff810612af>] warn_slowpath_common+0x7f/0xc0
    [ 131.191312] [<ffffffff8106130a>] warn_slowpath_null+0x1a/0x20
    [ 131.197131] [<ffffffff810b9fd5>] clockevents_program_event+0x135/0x140
    [ 131.203721] [<ffffffff810bb584>] tick_program_event+0x24/0x30
    [ 131.209534] [<ffffffff81089ab1>] hrtimer_interrupt+0x131/0x230
    [ 131.215437] [<ffffffff814b9600>] ? cpufreq_p4_target+0x130/0x130
    [ 131.221509] [<ffffffff81619119>] smp_apic_timer_interrupt+0x69/0x99
    [ 131.227839] [<ffffffff8161805d>] apic_timer_interrupt+0x6d/0x80
    [ 131.233816] <EOI> [<ffffffff81099745>] ? sched_clock_cpu+0xc5/0x120
    [ 131.240267] [<ffffffff814b9ff0>] ? cpuidle_wrap_enter+0x50/0xa0
    [ 131.246252] [<ffffffff814b9fe9>] ? cpuidle_wrap_enter+0x49/0xa0
    [ 131.252238] [<ffffffff814ba050>] cpuidle_enter_tk+0x10/0x20
    [ 131.257877] [<ffffffff814b9c89>] cpuidle_idle_call+0xa9/0x260
    [ 131.263692] [<ffffffff8101c42f>] cpu_idle+0xaf/0x120
    [ 131.268727] [<ffffffff815f8971>] start_secondary+0x255/0x257
    [ 131.274449] ---[ end trace 1151a50552231615 ]---

    When we change the system time to a low value like this, the value of
    timekeeper->offs_real will be a negative value.

    It seems that the WARN occurs because an hrtimer has been started in the time
    between the releasing of the timekeeper lock and the IPI call (via a call to
    on_each_cpu) in clock_was_set() in the do_settimeofday() code. The end result
    is that a REALTIME_CLOCK timer has been added with softexpires = expires =
    KTIME_MAX. The hrtimer_interrupt() fires/is called and the loop at
    kernel/hrtimer.c:1289 is executed. In this loop the code subtracts the
    clock base's offset (which was set to timekeeper->offs_real in
    do_settimeofday()) from the current hrtimer_cpu_base->expiry value (which
    was KTIME_MAX):

    KTIME_MAX - (a negative value) = overflow

    A simple check for an overflow can resolve this problem. Using KTIME_MAX
    instead of the overflow value will result in the hrtimer function being run,
    and the reprogramming of the timer after that.

    Cc: Thomas Gleixner <tglx@linutronix.de>
    Reviewed-by: Rik van Riel <riel@redhat.com>
    Signed-off-by: Prarit Bhargava <prarit@redhat.com>
    [jstultz: Tweaked commit subject]
    Signed-off-by: John Stultz <john.stultz@linaro.org>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    kernel/hrtimer.c | 2 ++
    1 file changed, 2 insertions(+)

    --- a/kernel/hrtimer.c
    +++ b/kernel/hrtimer.c
    @@ -1308,6 +1308,8 @@ retry:

    expires = ktime_sub(hrtimer_get_expires(timer),
    base->offset);
    + if (expires.tv64 < 0)
    + expires.tv64 = KTIME_MAX;
    if (expires.tv64 < expires_next.tv64)
    expires_next = expires;
    break;


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