Messages in this thread | | | Date | Wed, 16 Jul 2014 10:24:10 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [GIT PULL rcu/next] RCU commits for 3.17 |
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On Wed, Jul 16, 2014 at 11:57:27AM -0400, Pranith Kumar wrote: > On 07/16/2014 11:26 AM, 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@kernel.org> wrote: > >>> > >>>> > >>>> * Paul E. McKenney <paulmck@linux.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. > > > > Hi Paul, > > The other location where tick_nohz_full_mask is being allocated is in > tick_nohz_init_all(), called from tick_nohz_init(). rcu_init() is called before > tick_nohz_init() in init/main.c. CONFIG_NO_HZ_FULL_ALL for allocation of the > mask does not take effect when rcu_init() runs. > > So if nohz_full command line arg is not specified, tick_nohz_full_mask will > always be NULL when rcu_init() runs. So just checking for tick_nohz_full_mask > is NULL should be enough I guess.
Yep, that is indeed one of the conditions called out in the commit log below.
Thanx, Paul
> > 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? > > > > This may also be pulled from rcu/urgent in the -rcu git tree: > > > > git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git > > > > Thanx, Paul > > > > ------------------------------------------------------------------------ > > > > b/kernel/rcu/tree_plugin.h | 7 ++++--- > > 1 file changed, 4 insertions(+), 3 deletions(-) > > > > 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 NULL tick_nohz_full_mask otherwise. > > > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > > > > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h > > index f62b7f2f6abd..0f9ca12eabb9 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) > > did you mean #if defined(CONFIG_NO_HZ_FULL) && !defined(CONFIG_RCU_NOCB_CPU_ALL) > > > + if (tick_nohz_full_mask) > > + 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; > > > > -- > Pranith >
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