On Mon, Apr 08, 2013 at 01:19:23PM -0700, John Stultz wrote: > On 04/08/2013 05:47 AM, Prarit Bhargava wrote: > >2nd submit: I did quite a bit of testing with this patch and I don't see any > >ill effects. I've tested across several large and small x86 systems, and a > >ppc system for good measure. > > > >P. > > > >----8<--- > >` > >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. > > > >Signed-off-by: Prarit Bhargava <[email protected]> > >Cc: Thomas Gleixner <[email protected]> > >Cc: John Stultz <[email protected]> > > Prarit: Should this be tagged for -stable? > Please. I am hitting this problem with 3.8.6 on powerpc. The patch fixes it for me.
Tested-by: Guenter Roeck <[email protected]> Guenter -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
