Re: [tip:sched/urgent] sched: Check sched_domain before computinggroup power

From: Yinghai Lu
Date: Tue Nov 19 2013 - 18:36:22 EST

On Tue, Nov 19, 2013 at 11:15 AM, tip-bot for Srikar Dronamraju
<tipbot@xxxxxxxxx> wrote:
> Commit-ID: 9abf24d465180f5f2eb26a43545348262f16b771
> Gitweb: http://git.kernel.org/tip/9abf24d465180f5f2eb26a43545348262f16b771
> Author: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
> AuthorDate: Tue, 12 Nov 2013 22:11:26 +0530
> Committer: Ingo Molnar <mingo@xxxxxxxxxx>
> CommitDate: Tue, 19 Nov 2013 17:01:15 +0100
>
> sched: Check sched_domain before computing group power
>
> After commit 863bffc80898 ("sched/fair: Fix group power_orig
> computation"), we can dereference rq->sd before it is set.
>
> Fix this by falling back to power_of() in this case and add a comment
> explaining things.
>
> Signed-off-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
> [ Added comment and tweaked patch. ]
> Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: mikey@xxxxxxxxxxx
> Link: http://lkml.kernel.org/r/20131113151718.GN21461@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
> ---
> kernel/sched/fair.c | 27 ++++++++++++++++++++++++---
> 1 file changed, 24 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index e8b652e..fd773ad 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5379,10 +5379,31 @@ void update_group_power(struct sched_domain *sd, int cpu)
> */
>
> for_each_cpu(cpu, sched_group_cpus(sdg)) {
> - struct sched_group *sg = cpu_rq(cpu)->sd->groups;
> + struct sched_group_power *sgp;
> + struct rq *rq = cpu_rq(cpu);
>
> - power_orig += sg->sgp->power_orig;
> - power += sg->sgp->power;
> + /*
> + * build_sched_domains() -> init_sched_groups_power()
> + * gets here before we've attached the domains to the
> + * runqueues.
> + *
> + * Use power_of(), which is set irrespective of domains
> + * in update_cpu_power().
> + *
> + * This avoids power/power_orig from being 0 and
> + * causing divide-by-zero issues on boot.
> + *
> + * Runtime updates will correct power_orig.
> + */
> + if (unlikely(!rq->sd)) {
> + power_orig += power_of(cpu);
> + power += power_of(cpu);
> + continue;
> + }
> +
> + sgp = rq->sd->groups->sgp;
> + power_orig += sgp->power_orig;
> + power += sgp->power;
> }
> } else {
> /*

This one seems fix NULL reference in compute_group_power.

but get following on current Linus tree plus tip/sched/urgent.

divide error: 0000 [#1] SMP
[ 28.190477] Modules linked in:
[ 28.192012] CPU: 11 PID: 484 Comm: kworker/u324:0 Not tainted
3.12.0-yh-10487-g4b94e59-dirty #2044
[ 28.210488] Hardware name: Oracle Corporation Sun Fire
[ 28.229877] task: ffff88ff25205140 ti: ffff88ff2520a000 task.ti:
ffff88ff2520a000
[ 28.236139] RIP: 0010:[<ffffffff810d9ff4>] [<ffffffff810d9ff4>]
find_busiest_group+0x2b4/0x8a0
[ 28.252075] RSP: 0000:ffff88ff2520b9a8 EFLAGS: 00010046
[ 28.269591] RAX: 0000000000013fff RBX: 00000000ffffffff RCX: 00000000000000a0
[ 28.272977] RDX: 0000000000000000 RSI: 0000000000014000 RDI: 0000000000000050
[ 28.291968] RBP: ffff88ff2520bb08 R08: 00000000000003b6 R09: 0000000000000000
[ 28.309327] R10: 0000000000000000 R11: 0000000000000002 R12: ffff88ff2520ba90
[ 28.314222] R13: ffff887f2491c000 R14: 0000000000014000 R15: ffff88ff2520bba0
[ 28.331408] FS: 0000000000000000(0000) GS:ffff887f7d800000(0000)
knlGS:0000000000000000
[ 28.349333] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[ 28.351524] CR2: 0000000000000168 CR3: 0000000002c14000 CR4: 00000000000007e0
[ 28.370245] Stack:
[ 28.371466] 000000002520b9b8 000000000000000b 0000000000000048
0000000000000000
[ 28.389951] ffff887f2491c018 ffff88ff2520ba20 000000000000003c
00000000000002b6
[ 28.395085] 00000000000002b6 00000000000002b6 0000000000002df0
0000000100000001
[ 28.412079] Call Trace:
[ 28.413617] [<ffffffff810da798>] load_balance+0x1b8/0x8c0
[ 28.429692] [<ffffffff810ec67b>] ? __lock_acquire+0xadb/0xce0
[ 28.433037] [<ffffffff810db3c1>] idle_balance+0x101/0x1c0
[ 28.450328] [<ffffffff810db304>] ? idle_balance+0x44/0x1c0
[ 28.453420] [<ffffffff8214a13b>] __schedule+0x2cb/0xa10
[ 28.469847] [<ffffffff810e66d8>] ? trace_hardirqs_off_caller+0x28/0x160
[ 28.473782] [<ffffffff810e681d>] ? trace_hardirqs_off+0xd/0x10
[ 28.490654] [<ffffffff810d1c14>] ? local_clock+0x34/0x60
[ 28.493723] [<ffffffff810b837b>] ? worker_thread+0x2db/0x370
[ 28.510363] [<ffffffff8214f450>] ? _raw_spin_unlock_irq+0x30/0x40
[ 28.514002] [<ffffffff8214a935>] schedule+0x65/0x70
[ 28.530380] [<ffffffff810b8380>] worker_thread+0x2e0/0x370
[ 28.533450] [<ffffffff810ea19d>] ? trace_hardirqs_on+0xd/0x10
[ 28.550976] [<ffffffff810b80a0>] ? manage_workers.isra.17+0x330/0x330
[ 28.554356] [<ffffffff810bf598>] kthread+0x108/0x110
[ 28.571857] [<ffffffff810bf490>] ? __init_kthread_worker+0x70/0x70
[ 28.588961] [<ffffffff82157cec>] ret_from_fork+0x7c/0xb0
[ 28.592017] [<ffffffff810bf490>] ? __init_kthread_worker+0x70/0x70
[ 28.609904] Code: 89 85 b8 fe ff ff 49 8b 45 10 41 8b 7d 0c 44 8b
50 08 44 8b 70 04 89 f8 48 c1 e0 0a 45 89 d1 49 8d 44 01 ff 48 89 c2
48 c1 fa 3f <49> f7 f9 31 d2 49 89 c1 89 f8 44 89 f7 41 f7 f1 48 81 c7
00 02
[ 28.641210] RIP [<ffffffff810d9ff4>] find_busiest_group+0x2b4/0x8a0
[ 28.650476] RSP <ffff88ff2520b9a8>
[ 28.651754] divide error: 0000 [#2] [ 28.651762] ---[ end trace
bcaaa28065586d41 ]---
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