Messages in this thread Patch in this message |  | | | Date | Mon, 6 Feb 2012 08:44:28 -0800 | | From | Tejun Heo <> | | Subject | Re: [patch]block: fix ioc locking warning |
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Hello,
On Mon, Feb 06, 2012 at 11:37:21AM -0500, Vivek Goyal wrote: > block: Do not lock try to lock already locked queue again > > put_io_context() can be called with one of the request queue lock > already held. But if the locked queue's cic is not first in the > ioc->ioc_list, then we have two possible issues. > > - For above condition, current code bails out and schedules the worker > thread for freeing up ioc. This can be optimized. > > - It might happen that we received the queue locked but we still do the > trylock on the queue. For SMP case that's not a problem as we will > fail to lock already locked queue, but in case of UP, we seem to > succeed and in the process increment the preempt count. Once we are > done with ioc_exit_icq(), we do not call spin_unlock() on locked > queue as we are not supposed to. This leads to imbalance in preemtion > count and following warning was reported. > > This patch fixes both the above issues by making sure we do not try to > lock already locked queue again. > > 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 > > Signed-off-by: Shaohua Li <shaohua.li@intel.com> > Reported-by: Meelis Roos <mroos@linux.ee> > Reported-by: Knut Petersen <Knut_Petersen@t-online.de> > Tested-by: Knut Petersen <Knut_Petersen@t-online.de>
Yeah, this seems better to me. Jens, if you're gonna amend the commit, please consider collapsing the following patch into the original patch too. Thanks.
diff --git a/block/blk-ioc.c b/block/blk-ioc.c index 7490b6d..12978fc 100644 --- a/block/blk-ioc.c +++ b/block/blk-ioc.c @@ -204,7 +204,14 @@ void put_io_context(struct io_context *ioc, struct request_queue *locked_q) spin_unlock(last_q->queue_lock); last_q = NULL; - /* spin_trylock() always successes in UP case */ + /* + * If icq for locked_q wasn't at the head of + * icq_list, we can try to switch back to locked_q. + * On SMP, the following locked_q test avoids + * unnecessary deferring to release_work, on UP, + * incorrect lock state transition (trylock + * succeeding while holding the same lock). + */ if (this_q != locked_q && !spin_trylock(this_q->queue_lock)) break;
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