Messages in this thread |  | | | Date | Mon, 06 Feb 2012 17:09:05 +0100 | | From | Jens Axboe <> | | Subject | Re: [patch]block: fix ioc locking warning |
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On 02/06/2012 04:12 PM, Vivek Goyal wrote: > On Mon, Feb 06, 2012 at 03:50:11PM +0800, Shaohua Li wrote: >> Meelis reported a warning: >> >> WARNING: at kernel/timer.c:1122 run_timer_softirq+0x199/0x1ec() >> Hardware name: 939Dual-SATA2 >> timer: cfq_idle_slice_timer+0x0/0xaa preempt leak: 00000102 -> 00000103 >> Modules linked in: sr_mod cdrom videodev media drm_kms_helper ohci_hcd ehci_hcd v4l2_compat_ioctl32 usbcore i2c_ali15x3 snd_seq drm snd_timer snd_seq >> Pid: 0, comm: swapper Not tainted 3.3.0-rc2-00110-gd125666 #176 >> Call Trace: >> <IRQ> [<ffffffff81022aaa>] warn_slowpath_common+0x7e/0x96 >> [<ffffffff8114c485>] ? cfq_slice_expired+0x1d/0x1d >> [<ffffffff81022b56>] warn_slowpath_fmt+0x41/0x43 >> [<ffffffff8114c526>] ? cfq_idle_slice_timer+0xa1/0xaa >> [<ffffffff8114c485>] ? cfq_slice_expired+0x1d/0x1d >> [<ffffffff8102c124>] run_timer_softirq+0x199/0x1ec >> [<ffffffff81047a53>] ? timekeeping_get_ns+0x12/0x31 >> [<ffffffff810145fd>] ? apic_write+0x11/0x13 >> [<ffffffff81027475>] __do_softirq+0x74/0xfa >> [<ffffffff812f337a>] call_softirq+0x1a/0x30 >> [<ffffffff81002ff9>] do_softirq+0x31/0x68 >> [<ffffffff810276cf>] irq_exit+0x3d/0xa3 >> [<ffffffff81014aca>] smp_apic_timer_interrupt+0x6b/0x77 >> [<ffffffff812f2de9>] apic_timer_interrupt+0x69/0x70 >> <EOI> [<ffffffff81040136>] ? sched_clock_cpu+0x73/0x7d >> [<ffffffff81040136>] ? sched_clock_cpu+0x73/0x7d >> [<ffffffff8100801f>] ? default_idle+0x1e/0x32 >> [<ffffffff81008019>] ? default_idle+0x18/0x32 >> [<ffffffff810008b1>] cpu_idle+0x87/0xd1 >> [<ffffffff812de861>] rest_init+0x85/0x89 >> [<ffffffff81659a4d>] start_kernel+0x2eb/0x2f8 >> [<ffffffff8165926e>] x86_64_start_reservations+0x7e/0x82 >> [<ffffffff81659362>] x86_64_start_kernel+0xf0/0xf7 >> >> this_q == locked_q is possible. There are two problems here: >> 1. In UP case, there is preemption counter issue as spin_trylock always >> successes. >> 2. In SMP case, the loop breaks too earlier. > > Thanks Shaohua. So is it the case where there are more than one cic's on > ioc->ioc_list and first cic's queue is not same as locked_queue. But some > other cic other than first has queue same as locked_queue. > > In that case current code will still defer freeing of ioc and cic to a > worker thread. So this patch will introduce one optimization to handle > those cases and avoid calling worker thread. > > Secondly it fixes the discrepancy of preemption count on UP machines, > where we have one extra preemption count after finish of function > put_io_context(). So for UP case spin_trylock() increases the preemption > count and always returns success. As this_q == locked_q we never try to do > unlock on this queue and hence never decrement the preemption count > hence resulting in preemption count warning. > > Changlog was not obivious atleast to me. I wished it was little more > descriptive. Anyway, patch is already committed..
We can always amend the changelog, so don't worry about it already being committed. If you want to add/change something, just send it in.
-- Jens Axboe
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