linux-kernel - Re: [PATCH] uio: Fix uio driver to refcount device

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Date:	Wed, 11 Mar 2015 16:15:58 +0000
From:	Brian Russell <brian.russell@...cade.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Brian Russell <brussell@...cade.com>
CC:	"Hans J. Koch" <hjk@...sjkoch.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] uio: Fix uio driver to refcount device



On 11/03/15 16:02, Greg Kroah-Hartman wrote:
> On Wed, Mar 11, 2015 at 03:59:36PM +0000, Brian Russell wrote:
>>
>>
>> On 11/03/15 15:43, Greg Kroah-Hartman wrote:
>>> On Wed, Mar 11, 2015 at 03:31:42PM +0000, Brian Russell wrote:
>>>> Protect uio driver from crashing if its owner is hot unplugged while there
>>>> are open fds.
>>>> Signed-off-by: Brian Russell <brussell@...cade.com>
>>>
>>> Minor nit, you need a blank line before your s-o-b: line.
>>>
>>
>> Ack.
>>
>>>
>>>
>>>> ---
>>>>  drivers/uio/uio.c | 8 +++++++-
>>>>  1 file changed, 7 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
>>>> index 6276f13..70ce015 100644
>>>> --- a/drivers/uio/uio.c
>>>> +++ b/drivers/uio/uio.c
>>>> @@ -434,9 +434,11 @@ static int uio_open(struct inode *inode, struct file *filep)
>>>>  		goto out;
>>>>  	}
>>>>  
>>>> +	get_device(idev);
>>>
>>> What is the real oops caused when a device is removed?  Protecting this
>>> with a reference count seems ok, but it seems "heavy".
>>>
>>
>> I'm seeing it with PCI hotplug. The PCI subsystem calls remove and the
>> owner module in turn calls uio_unregister_device while app stil has
>> open fds.
> 
> Sorry, I meant, what exactly is the oops message, with the callback?
> What portion of code is crashing because we have an open fd?  The pci
> remove path of the UIO core should be fixed to handle this properly.
> Not to say that your patch isn't correct, just want to see the crash to
> know for sure.
> 

Ah, I see, sorry:

 [  168.890968] BUG: unable to handle kernel paging request at ffff8800b2fb7e70
[  168.893141] IP: [<ffffffff810b5acc>] module_put+0xc/0x20
[  168.894076] PGD 1bc8067 PUD 0 
[  168.894679] Oops: 0002 [#1] SMP 
[  168.895322] Modules linked in: igb_uio(O) xfrm_user xfrm_algo l2tp_ip6 l2tp_ip l2tp_eth l2tp_netlink l2tp_core tun uio cpufreq_userspace cpufreq_powersave cpufreq_ondemand cpufreq_conservative ipv6 crc32_pclmul microcode aesni_intel aes_x86_64 lrw gf128mul glue_helper serio_raw ablk_helper ghash_clmulni_intel intel_agp intel_gtt psmouse virtio_console processor agpgart cryptd evdev button i2c_piix4 i2c_core pcspkr thermal_sys virtio_balloon usb_storage ohci_hcd squashfs loop hid_generic usbhid hid pata_acpi ata_generic virtio_blk virtio_net floppy ata_piix virtio_pci virtio_ring virtio crc32c_intel [last unloaded: igb_uio]
[  168.900849] CPU: 0 PID: 4494 Comm: dataplane Tainted: G        W  O 3.14.33-1-amd64-vyatta #1
[  168.900849] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.7.5-20140531_083030-gandalf 04/01/2014
[  168.900849] task: ffff880036bb60b0 ti: ffff880036956000 task.ti: ffff880036956000
[  168.900849] RIP: 0010:[<ffffffff810b5acc>]  [<ffffffff810b5acc>] module_put+0xc/0x20
[  168.900849] RSP: 0018:ffff880036957ea0  EFLAGS: 00010282
[  168.900849] RAX: 00000000333b7e68 RBX: ffff880036d61ce0 RCX: 0000000000000001
[  168.900849] RDX: 0000000000000000 RSI: ffff880079c92800 RDI: ffff880078dfbb98
[  168.900849] RBP: ffff880078dfbb98 R08: 0000000000000000 R09: 0000000000000000
[  168.900849] R10: ffffffff8110da65 R11: 0000000000000001 R12: 0000000000000000
[  168.900849] R13: ffff88004be4c540 R14: ffff88007c8957a0 R15: ffff880079c92810
[  168.900849] FS:  00007fc28b9f7700(0000) GS:ffff88007fc00000(0000) knlGS:0000000000000000
[  168.900849] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  168.900849] CR2: ffff8800b2fb7e70 CR3: 00000000368f9000 CR4: 00000000000406f0
[  168.900849] Stack:
[  168.900849]  ffffffffa0191383 ffff880079c92800 0000000000000008 ffff88004fec9c30
[  168.900849]  ffffffff811431e8 ffffffff81082810 0000000000000000 ffffffff81ac0a50
[  168.900849]  ffff880036bb6ba0 ffff880036bb60b0 0000000001a8dc80 0000000000000003
[  168.900849] Call Trace:
[  168.900849]  [<ffffffffa0191383>] ? uio_release+0x43/0x70 [uio]
[  168.900849]  [<ffffffff811431e8>] ? __fput+0xc8/0x230
[  168.900849]  [<ffffffff81082810>] ? sched_clock_cpu+0x90/0xc0
[  168.900849]  [<ffffffff810707c7>] ? task_work_run+0x97/0xd0
[  168.900849]  [<ffffffff8100ceaa>] ? do_notify_resume+0x8a/0xb0
[  168.900849]  [<ffffffff814d5272>] ? int_signal+0x12/0x17
[  168.900849] Code: 48 89 de 48 c7 c7 c0 5b 70 81 31 c0 e8 8e 61 41 00 eb d9 66 66 66 2e 0f 1f 84 00 00 00 00 00 48 85 ff 74 0c 48 8b 87 28 02 00 00 <65> 48 ff 40 08 f3 c3 66 66 66 66 2e 0f 1f 84 00 00 00 00 00 41 
[  168.900849] RIP  [<ffffffff810b5acc>] module_put+0xc/0x20
[  168.900849]  RSP <ffff880036957ea0>
[  168.900849] CR2: ffff8800b2fb7e70
[  168.900849] ---[ end trace 20f273e64b20b382 ]---
[  168.900849] Kernel panic - not syncing: Fatal exception
[  168.900849] Kernel Offset: 0x0 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffff9fffffff)
[  168.900849] Rebooting in 60 seconds..



> thanks,
> 
> greg k-h
> 
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