linux-kernel - divide error trying to set rt

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Message-Id: <1214432249.5464.22.camel@Palanthas.Krynn>
Date:	Thu, 26 Jun 2008 00:17:27 +0200
From:	Dario Faggioli <raistlin@...ux.it>
To:	Michael Trimarchi <trimarchimichael@...oo.it>,
	PeterZijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>, "Daniel K." <dk@...no>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: divide error trying to set rt_period to zero

Hi all again,

Here it is another little Oops we found:

echo 0 > /dev/cgroups/0/cpu.rt_period_us
or
echo 4294967296 > /dev/cgroups/0/cpu.rt_period_us

[  205.509825] divide error: 0000 [#1] 
[  205.510151] Modules linked in:
[  205.510151] 
[  205.510151] Pid: 2339, comm: bash Not tainted (2.6.26-rc8 #33)
[  205.510151] EIP: 0060:[<c030c6ef>] EFLAGS: 00000293 CPU: 0
[  205.510151] EIP is at div64_u64+0x5f/0x70
[  205.510151] EAX: 0000389f EBX: 00000000 ECX: 00000000 EDX: 00000000
[  205.510151] ESI: d9800000 EDI: 00000000 EBP: c6cede60 ESP: c6cede50
[  205.510151]  DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 0068
[  205.510151] Process bash (pid: 2339, ti=c6cec000 task=c79be370 task.ti=c6cec000)
[  205.510151] Stack: d9800000 0000389f c05971a0 d9800000 c6cedeb4 c0214dbd 00000000 00000000 
[  205.510151]        c6cede88 c0242bd8 c05377c0 c7a41b40 00000000 00000000 00000000 c05971a0 
[  205.510151]        c780ed20 c7508494 c7a41b40 00000000 00000002 c6cedebc c05971a0 ffffffea 
[  205.510151] Call Trace:
[  205.510151]  [<c0214dbd>] ? __rt_schedulable+0x1cd/0x240
[  205.510151]  [<c0242bd8>] ? cgroup_file_open+0x18/0xe0
[  205.510151]  [<c0214fe4>] ? tg_set_bandwidth+0xa4/0xf0
[  205.510151]  [<c0215066>] ? sched_group_set_rt_period+0x36/0x50
[  205.510151]  [<c021508e>] ? cpu_rt_period_write_uint+0xe/0x10
[  205.510151]  [<c0242dc5>] ? cgroup_file_write+0x125/0x160
[  205.510151]  [<c0232c15>] ? hrtimer_interrupt+0x155/0x190
[  205.510151]  [<c02f047f>] ? security_file_permission+0xf/0x20
[  205.510151]  [<c0277ad8>] ? rw_verify_area+0x48/0xc0
[  205.510151]  [<c0283744>] ? dupfd+0x104/0x130
[  205.510151]  [<c027838c>] ? vfs_write+0x9c/0x160
[  205.510151]  [<c0242ca0>] ? cgroup_file_write+0x0/0x160
[  205.510151]  [<c027850d>] ? sys_write+0x3d/0x70
[  205.510151]  [<c0203019>] ? sysenter_past_esp+0x6a/0x91
[  205.510151]  =======================
[  205.510151] Code: 0f 45 de 31 f6 0f ad d0 d3 ea f6 c1 20 0f 45 c2 0f 45 d6 89 45 f0 89 55 f4 8b 55 f4 31 c9 8b 45 f0 39 d3 89 c6 77 08 89 d0 31 d2 <f7> f3 89 c1 83 c4 08 89 f0 f7 f3 89 ca 5b 5e 5d c3 55 89 e5 56 
[  205.510151] EIP: [<c030c6ef>] div64_u64+0x5f/0x70 SS:ESP 0068:c6cede50

The attached patch solves the issue for me.

I'm checking as soon as possible for the period not being zero since, if
it is, going ahead is useless. This way we also save a mutex_lock() and
a read_lock() wrt doing it inside tg_set_bandwidth() or
__rt_schedulable().

Regards,
Dario Faggioli

Signed-off-by: Dario Faggioli <raistlin@...ux.it>
Signed-off-by: Michael Trimarchi <trimarchimichael@...oo.it>
---
diff --git a/kernel/sched.c b/kernel/sched.c
index 3aaa5c8..9c3df51 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -8501,6 +8501,9 @@ int sched_group_set_rt_period(struct task_group
*tg, long rt_period_us)
 	rt_period = (u64)rt_period_us * NSEC_PER_USEC;
 	rt_runtime = tg->rt_bandwidth.rt_runtime;
 
+	if (period == 0)
+		return -EINVAL;
+
 	return tg_set_bandwidth(tg, rt_period, rt_runtime);
 }

-- 
<<This happens because I choose it to happen!>>
(Raistlin Majere, DragonLance Chronicles -Dragons of Spring Drawning-)
----------------------------------------------------------------------
Dario Faggioli
GNU/Linux Registered User: #340657
Web: http://www.linux.it/~raistlin
Blog: http://blog.linux.it/raistlin
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             raistlin@...ga.net
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