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Message-ID: <20140716193647.GA16219@linux.vnet.ibm.com>
Date: Wed, 16 Jul 2014 12:36:47 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Ingo Molnar <mingo@...nel.org>
Cc: linux-kernel@...r.kernel.org, fabf@...net.be,
bobby.prani@...il.com, davidshan@...cent.com, joe@...ches.com,
keescook@...omium.org, Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [GIT PULL rcu/next] RCU commits for 3.17
On Wed, Jul 16, 2014 at 08:26:29AM -0700, Paul E. McKenney wrote:
> On Wed, Jul 16, 2014 at 07:17:07AM -0700, Paul E. McKenney wrote:
> > On Wed, Jul 16, 2014 at 03:13:22PM +0200, Ingo Molnar wrote:
> > >
> > > * Ingo Molnar <mingo@...nel.org> wrote:
> > >
> > > >
> > > > * Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:
> > > >
> > > > > Hello, Ingo,
> > > > >
> > > > > The changes in this series include:
> > > > >
> > > > > 1. Update RCU documentation. These were posted to LKML at
> > > > > https://lkml.org/lkml/2014/7/7/650.
> > > > >
> > > > > 2. Miscellaneous fixes. These were posted to LKML at
> > > > > https://lkml.org/lkml/2014/7/7/678.
> > > > >
> > > > > 3. Maintainership changes. These were posted to LKML at
> > > > > https://lkml.org/lkml/2014/7/7/713, with a couple of
> > > > > additional at https://lkml.org/lkml/2014/7/3/812 and
> > > > > https://lkml.org/lkml/2014/6/2/585.
> > > > >
> > > > > 4. Torture-test updates. These were posted to LKML at
> > > > > https://lkml.org/lkml/2014/7/7/816.
> > > > >
> > > > > 5. Callback-offloading changes. These were posted to LKML at
> > > > > https://lkml.org/lkml/2014/7/7/1007.
> > > > >
> > > > > All of these have been exposed to -next testing.
> > >
> > > JFYI, the attached x86 (rand!-) config crashes on early bootup:
> > >
> > > [ 0.000000] RCU: Adjusting geometry for rcu_fanout_leaf=16, nr_cpu_ids=2
> > > [ 0.000000] ------------[ cut here ]------------
> > > [ 0.000000] WARNING: CPU: 0 PID: 0 at arch/x86/kernel/cpu/common.c:1439 warn_pre_alternatives+0x1e/0x20()
> > > [ 0.000000] You're using static_cpu_has before alternatives have run!
> > > [ 0.000000] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.16.0-rc5+ #236363
> > > [ 0.000000] Hardware name: System manufacturer System Product Name/A8N-E, BIOS ASUS A8N-E ACPI BIOS Revision 1008 08/22/2005
> > > [ 0.000000] 0000000000000000 ffffffff82787c60 ffffffff81ff4ec0 ffffffff82787ca8
> > > [ 0.000000] ffffffff82787c98 ffffffff810651ac ffffffff81011531 ffffffff82787e48
> > > [ 0.000000] 0000000000000000 0000000000000000 ffffffff827cf880 ffffffff82787cf8
> > > [ 0.000000] Call Trace:
> > > [ 0.000000] [<ffffffff81ff4ec0>] dump_stack+0x4d/0x66
> > > [ 0.000000] [<ffffffff810651ac>] warn_slowpath_common+0x7a/0x93
> > > [ 0.000000] [<ffffffff81011531>] ? warn_pre_alternatives+0x1e/0x20
> > > [ 0.000000] [<ffffffff81065239>] warn_slowpath_fmt+0x4c/0x4e
> > > [ 0.000000] [<ffffffff82005817>] ? irq_return+0x7/0x7
> > > [ 0.000000] [<ffffffff81011531>] warn_pre_alternatives+0x1e/0x20
> > > [ 0.000000] [<ffffffff81033d31>] __do_page_fault+0xc3/0x43f
> > > [ 0.000000] [<ffffffff81005347>] ? print_context_stack+0x6a/0xb6
> > > [ 0.000000] [<ffffffff810045f1>] ? dump_trace+0x27d/0x294
> > > [ 0.000000] [<ffffffff815b185b>] ? number.isra.1+0x127/0x22c
> > > [ 0.000000] [<ffffffff8109abe2>] ? print_time.part.5+0x58/0x5c
> > > [ 0.000000] [<ffffffff81086a9a>] ? sched_clock_cpu+0x11/0xb9
> > > [ 0.000000] [<ffffffff810340ef>] do_page_fault+0x1e/0x54
> > > [ 0.000000] [<ffffffff82005817>] ? irq_return+0x7/0x7
> > > [ 0.000000] [<ffffffff82006872>] page_fault+0x22/0x30
> > > [ 0.000000] [<ffffffff815b65fa>] ? __bitmap_or+0x15/0x28
> > > [ 0.000000] [<ffffffff82c876f0>] rcu_init_one+0x4c0/0x55d
> > > [ 0.000000] [<ffffffff82c87b00>] rcu_init+0x270/0x2da
> > > [ 0.000000] [<ffffffff82c6ec82>] start_kernel+0x24f/0x4d2
> > > [ 0.000000] [<ffffffff82c6e841>] ? set_init_arg+0x53/0x53
> > > [ 0.000000] [<ffffffff82c6e453>] x86_64_start_reservations+0x2a/0x2c
> > > [ 0.000000] [<ffffffff82c6e546>] x86_64_start_kernel+0xf1/0xf4
> > > [ 0.000000] ---[ end trace 4650963e41188009 ]---
> > > [ 0.000000] BUG: unable to handle kernel NULL pointer dereference at (null)
> > > [ 0.000000] IP: [<ffffffff815b65fa>] __bitmap_or+0x15/0x28
> > > [ 0.000000] PGD 0
> > > [ 0.000000] Oops: 0000 [#1] SMP DEBUG_PAGEALLOC
> > > [ 0.000000] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G W 3.16.0-rc5+ #236363
> > > [ 0.000000] Hardware name: System manufacturer System Product Name/A8N-E, BIOS ASUS A8N-E ACPI BIOS Revision 1008 08/22/2005
> > > [ 0.000000] task: ffffffff827a3480 ti: ffffffff82784000 task.ti: ffffffff82784000
> > > [ 0.000000] RIP: 0010:[<ffffffff815b65fa>] [<ffffffff815b65fa>] __bitmap_or+0x15/0x28
> > > [ 0.000000] RSP: 0000:ffffffff82787ef8 EFLAGS: 00010002
> > > [ 0.000000] RAX: 0000000000000000 RBX: 00000000ffffffff RCX: 0000000000000001
> > > [ 0.000000] RDX: 0000000000000000 RSI: ffff880000019800 RDI: ffff880000019800
> > > [ 0.000000] RBP: ffffffff82787ef8 R08: 0000000000000000 R09: 0000000000000000
> > > [ 0.000000] R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff827cf880
> > > [ 0.000000] R13: 0000000000000002 R14: ffffffff827cf880 R15: 00000000001cd000
> > > [ 0.000000] FS: 0000000000000000(0000) GS:ffff88003f800000(0000) knlGS:0000000000000000
> > > [ 0.000000] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> > > [ 0.000000] CR2: 0000000000000000 CR3: 000000000279e000 CR4: 00000000000006b0
> > > [ 0.000000] Stack:
> > > [ 0.000000] ffffffff82787f50 ffffffff82c876f0 ffffffff83b7e7a0 0000000000000001
> > > [ 0.000000] 0000000000000082 0000000200000000 00000000ffffffff ffffffff82d37920
> > > [ 0.000000] ffff88003ffbba40 ffffffff82d3e890 0000000000000000 ffffffff82787f80
> > > [ 0.000000] Call Trace:
> > > [ 0.000000] [<ffffffff82c876f0>] rcu_init_one+0x4c0/0x55d
> > > [ 0.000000] [<ffffffff82c87b00>] rcu_init+0x270/0x2da
> > > [ 0.000000] [<ffffffff82c6ec82>] start_kernel+0x24f/0x4d2
> > > [ 0.000000] [<ffffffff82c6e841>] ? set_init_arg+0x53/0x53
> > > [ 0.000000] [<ffffffff82c6e453>] x86_64_start_reservations+0x2a/0x2c
> > > [ 0.000000] [<ffffffff82c6e546>] x86_64_start_kernel+0xf1/0xf4
> > > [ 0.000000] Code: 4c 89 04 c7 4d 09 c1 48 ff c0 eb e8 31 c0 4d 85 c9 0f 95 c0 5d c3 55 48 63 c9 31 c0 48 83 c1 3f 48 89 e5 48 c1 e9 06 39 c1 7e 11 <4c> 8b 04 c2 4c 0b 04 c6 4c 89 04 c7 48 ff c0 eb eb 5d c3 55 48
> > > [ 0.000000] RIP [<ffffffff815b65fa>] __bitmap_or+0x15/0x28
> > > [ 0.000000] RSP <ffffffff82787ef8>
> > > [ 0.000000] CR2: 0000000000000000
> > > [ 0.000000] ---[ end trace 4650963e4118800a ]---
> > > [ 0.000000] Kernel panic - not syncing: Attempted to kill the idle task!
> > > [ 0.000000] Rebooting in 1 seconds..Press any key to enter the menu
> > >
> > > Excluding the new RCU bits from tip:master makes it boot.
> > >
> > > Any idea what's wrong?
> >
> > Looks like you have a setup that has NO_HZ_FULL=y, but that somehow
> > avoids having a non-NULL tick_nohz_full_mask at rcu_init() time. But you
> > probably knew that already. And of course when I test locally with the
> > same RCU-related and NO_HZ_FULL-related configs, it all works just fine.
> > Perhaps there is some interaction with some other code in -tip.
> >
> > So let's see...
> >
> > Now your .config has CONFIG_NO_HZ_FULL_ALL=y and therefore also has
> > CONFIG_RCU_NOCB_CPU_ALL=y. In that case, there is no point in doing the
> > cpumask_or() because all the bits are already set. So the only time
> > that this cpumask_or() matters is when CONFIG_RCU_NOCB_CPU_ALL==n and
> > an explicit nohz_full= mask was specified at boot time. So one reasonable
> > change is to replace the #ifndef guarding the cpumask_or() with:
> >
> > #if defined(CONFIG_NO_HZ_FULL) && !defined(CONFIG_RCU_NOCB_CPU_ALL)
> >
> > I am now looking to see how tick_nohz_full_mask might be NULL in this
> > situation. Depending on what I find, I might insert a check for that.
>
> And of course if you don't actually specify a nohz_full= mask, then
> tick_nohz_full_mask can be NULL at RCU initialization time, and if it
> is also true that CONFIG_NO_HZ_FULL_ALL=n, this condition can persist
> forever.
>
> Does the following patch on top of 1823172ab582 (Merge branches
> 'doc.2014.07.08a', 'fixes.2014.07.09a', 'maintainers.2014.07.08b',
> 'nocbs.2014.07.07a' and 'torture.2014.07.07a' into HEAD) fix the
> problem?
Sigh. I needed to have tested sooner with CONFIG_CPUMASK_OFFSTACK=n.
Fortunately, Fengguang Wu's scripts never forget. ;-)
So the following patch should work better. The earlier one was prone
to ORing garbage into the rcu_nocb_mask on !CONFIG_CPUMASK_OFFSTACK
&& CONFIG_NO_HZ && !CONFIG_NO_HZ_ALL builds that were booted without
the nohz_full= kernel parameter.
Thanx, Paul
------------------------------------------------------------------------
rcu: Allow for NULL tick_nohz_full_mask when nohz_full= missing
If there isn't a nohz_full= kernel parameter specified, then
tick_nohz_full_mask can legitimately be NULL. This can cause
problems when RCU's boot code tries to cpumask_or() this value into
rcu_nocb_mask. In addition, if NO_HZ_FULL_ALL=y, there is no point
in doing the cpumask_or() in the first place because this will cause
RCU_NOCB_CPU_ALL=y, which in turn will have all bits already set in
rcu_nocb_mask.
This commit therefore avoids the cpumask_or() if NO_HZ_FULL_ALL=y
and checks for !tick_nohz_full_running otherwise, this latter check
catching cases when there was no nohz_full= kernel parameter specified.
Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index f62b7f2f6abd..00dc411e9676 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2479,9 +2479,10 @@ static void __init rcu_spawn_nocb_kthreads(struct rcu_state *rsp)
if (rcu_nocb_mask == NULL)
return;
-#ifdef CONFIG_NO_HZ_FULL
- cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
-#endif /* #ifdef CONFIG_NO_HZ_FULL */
+#if defined(CONFIG_NO_HZ_FULL) && !defined(CONFIG_NO_HZ_FULL_ALL)
+ if (tick_nohz_full_running)
+ cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask);
+#endif /* #if defined(CONFIG_NO_HZ_FULL) && !defined(CONFIG_NO_HZ_FULL_ALL) */
if (ls == -1) {
ls = int_sqrt(nr_cpu_ids);
rcu_nocb_leader_stride = ls;
--
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