netdev - Re: [RFC] bonding: fix workqueue re-arming races

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Date:	Fri, 1 Oct 2010 20:22:32 +0200
From:	Jiri Bohac <jbohac@...e.cz>
To:	Narendra K <Narendra_K@...l.com>
Cc:	Jay Vosburgh <fubar@...ibm.com>, Jiri Bohac <jbohac@...e.cz>,
	bonding-devel@...ts.sourceforge.net, markine@...gle.com,
	jarkao2@...il.com, chavey@...gle.com, netdev@...r.kernel.org
Subject: Re: [RFC] bonding: fix workqueue re-arming races

On Fri, Sep 24, 2010 at 06:23:53AM -0500, Narendra K wrote:
> On Fri, Sep 17, 2010 at 04:14:33AM +0530, Jay Vosburgh wrote:
> > Jay Vosburgh <fubar@...ibm.com> wrote:
> The follwing call trace was seen -
> 
> 2.6.35.with.upstream.patch-next-20100811-0.7-default+
> [14602.945876] ------------[ cut here ]------------
> [14602.950474] kernel BUG at kernel/workqueue.c:2844!
> [14602.955242] invalid opcode: 0000 [#1] SMP 
> [14602.959341] last sysfs file: /sys/class/net/bonding_masters
> [14602.964888] CPU 1 
> [14602.966714] Modules linked in: af_packet bonding ipv6 cpufreq_conservative cpufreq_userspace cpufreq_powersave acpi_cpufreq mperf microcode fuse loop dm_mod joydev usbhid hid bnx2 tpm_tis tpm tpm_bios rtc_cmos iTCO_wdt iTCO_vendor_support sr_mod power_meter cdrom sg serio_raw mptctl pcspkr rtc_core usb_storage dcdbas rtc_lib button uhci_hcd ehci_hcd usbcore sd_mod crc_t10dif edd ext3 mbcache jbd fan processor ide_pci_generic ide_core ata_generic ata_piix libata mptsas mptscsih mptbase scsi_transport_sas scsi_mod thermal thermal_sys hwmon
> [14603.015002] 
> [14603.016524] Pid: 4006, comm: ifdown-bonding Not tainted 2.6.35.with.upstream.patch-next-20100811-0.7-default+ #2 0M233H/PowerEdge R710
> [14603.028554] RIP: 0010:[<ffffffff81067b50>]  [<ffffffff81067b50>] destroy_workqueue+0x1d0/0x1e0
> [14603.037144] RSP: 0018:ffff88022a379d88  EFLAGS: 00010286
> [14603.042432] RAX: 000000000000003c RBX: ffff880228674240 RCX: ffff880228f0e800
> [14603.049534] RDX: 0000000000001000 RSI: 0000000000000002 RDI: 000000000000001a
> [14603.056638] RBP: ffff88022a379da8 R08: ffff88022a379cf8 R09: 0000000000000000
> [14603.063741] R10: 00000000ffffffff R11: 0000000000000000 R12: 0000000000000002
> [14603.070842] R13: ffffffff817b8560 R14: ffff8802299d1480 R15: ffff8802299d1488
> [14603.077944] FS:  00007f8e6a28f700(0000) GS:ffff880001c00000(0000) knlGS:0000000000000000
> [14603.085999] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> [14603.091719] CR2: 00007f8e6a2c2000 CR3: 0000000127d1c000 CR4: 00000000000006e0
> [14603.098822] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [14603.105924] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> [14603.113026] Process ifdown-bonding (pid: 4006, threadinfo ffff88022a378000, task ffff8802299b0080)
> [14603.121944] Stack:
> [14603.123944]  ffff88022a379da8 ffff8802299d1000 ffff8802299d1000 000000010036b6a4
> [14603.131182] <0> ffff88022a379dc8 ffffffffa030a91d ffff8802299d1000 000000010036b6a4
> [14603.138857] <0> ffff88022a379e28 ffffffff812e0a08 ffff88022a379e38 ffff88022a379de8
> [14603.146718] Call Trace:
> [14603.149158]  [<ffffffffa030a91d>] bond_destructor+0x1d/0x30 [bonding]
> [14603.155572]  [<ffffffff812e0a08>] netdev_run_todo+0x1a8/0x270
> [14603.161293]  [<ffffffff812ee859>] rtnl_unlock+0x9/0x10
> [14603.166411]  [<ffffffffa0317824>] bonding_store_bonds+0x1c4/0x1f0 [bonding]
> [14603.173342]  [<ffffffff810f26be>] ? alloc_pages_current+0x9e/0x110
> [14603.179497]  [<ffffffff81285c9e>] class_attr_store+0x1e/0x20
> [14603.185132]  [<ffffffff8116e365>] sysfs_write_file+0xc5/0x140
> [14603.190853]  [<ffffffff8110a68f>] vfs_write+0xcf/0x190
> [14603.195967]  [<ffffffff8110a840>] sys_write+0x50/0x90
> [14603.200996]  [<ffffffff81002ec2>] system_call_fastpath+0x16/0x1b
> [14603.206974] Code: 00 7f 14 8b 3b eb 91 3d 00 10 00 00 89 c2 77 10 8b 3b e9 07 ff ff ff 3d 00 10 00 00 89 c2 76 f0 8b 3b e9 a9 fe ff ff 0f 0b eb fe <0f> 0b eb fe 66 66 66 2e 0f 1f 84 00 00 00 00 00 55 48 8b 3d 00 
> [14603.226419] RIP  [<ffffffff81067b50>] destroy_workqueue+0x1d0/0x1e0
> [14603.232669]  RSP <ffff88022a379d88>
> [    0.000000] Initializing cgroup subsys cpuset
> [    0.000000] Initializing cgroup subsys cpu

This should be the BUG_ON(cwq->nr_active) in
destroy_workqueue()

This is really strange. bondng_store_bonds() can do two things:
create or delete a bonding device.

I checked the delete path, where I would normally expect such a
problem, but I can't find a way it could fail in this way.
bondng_store_bonds() calls unregister_netdevice(), which 
- calls rollback_registered() -> bond_close()
- puts the device on the net_todo_list.
On rtnl_unlock() netdev_run_todo() gets called and that calls 
bond_destructor().

bond_close() now makes sure the rearming work items are not
pending, thus, the only work items that may still be pending on
the workqueue are the non-rearming "commit" work items.
flush_workqueue(), called at the beginning of destroy_workqueue()
should have waited for these to finish.
If all of the above is correct, this BUG_ON should never trigger.

Maybe I am overlooking something, or it may be some kind of
failure/race condition in the create path, resulting in
bond_destructor() being called as well.

Narendra, any chance to capture the dmesg lines preceeding the
BUG message? This should show which of the above cases it is.

I will try to come up with a debug patch that will tell us which
work remains active on the work queue.

-- 
Jiri Bohac <jbohac@...e.cz>
SUSE Labs, SUSE CZ

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