RE: [hyperv] BUG at drivers/hv/channel.c:462 while changing MTU

[KY Srinivasan]

> -----Original Message-----
> From: Richard Weinberger [mailto:richard@xxxxxx]
> Sent: Monday, August 25, 2014 8:07 AM
> To: KY Srinivasan; Sitsofe Wheeler
> Cc: Haiyang Zhang; Greg Kroah-Hartman; devel@xxxxxxxxxxxxxxxxxxxxxx;
> linux-kernel@xxxxxxxxxxxxxxx; Jason Wang; Daniel Borkmann; David S. Miller;
> netdev@xxxxxxxxxxxxxxx
> Subject: Re: [hyperv] BUG at drivers/hv/channel.c:462 while changing MTU
> 
> Am 25.08.2014 16:53, schrieb KY Srinivasan:
> >
> >
> >> -----Original Message-----
> >> From: Richard Weinberger [mailto:richard.weinberger@xxxxxxxxx]
> >> Sent: Monday, August 25, 2014 3:48 AM
> >> To: Sitsofe Wheeler
> >> Cc: Haiyang Zhang; KY Srinivasan; Greg Kroah-Hartman;
> >> devel@xxxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Jason
> >> Wang; Daniel Borkmann; David S. Miller; netdev@xxxxxxxxxxxxxxx
> >> Subject: Re: [hyperv] BUG at drivers/hv/channel.c:462 while changing
> >> MTU
> >>
> >>  via
> >>
> >>
> >> On Wed, Aug 20, 2014 at 5:41 AM, Sitsofe Wheeler <sitsofe@xxxxxxxxx>
> >> wrote:
> >>> Aug 20 04:04:41 ubuntuhv kernel: [    9.230399] random: nonblocking pool
> is
> >> initialized
> >>> Aug 20 04:04:41 ubuntuhv kernel: [   10.338487] EXT4-fs (sda1): re-
> >> mounted. Opts: errors=remount-ro
> >>> Aug 20 04:04:41 ubuntuhv kernel: [   11.099094] hv_storvsc vmbus_0_1:
> >> cmd 0x85 scsi status 0x2 srb status 0x6
> >>> Aug 20 04:04:41 ubuntuhv kernel: [   11.099901] hv_storvsc vmbus_0_1:
> >> cmd 0x85 scsi status 0x2 srb status 0x6
> >>> Aug 20 04:04:43 ubuntuhv kernel: [   12.999830] psmouse serio1:
> trackpoint:
> >> IBM TrackPoint firmware: 0x01, buttons: 0/0
> >>> Aug 20 03:55:47 ubuntuhv kernel: [   13.003659] input: TPPS/2 IBM
> >> TrackPoint as /devices/platform/i8042/serio1/input/input4
> >>> Aug 20 03:57:28 ubuntuhv kernel: [  113.711832] hv_netvsc vmbus_0_14:
> >>> net device safe to remove Aug 20 03:57:28 ubuntuhv kernel: [
> >>> 113.713882] hv_netvsc: hv_netvsc channel opened successfully Aug 20
> >>> 03:57:29 ubuntuhv kernel: [  114.961312] hv_netvsc vmbus_0_14: Send
> >>> section size: 6144, Section count:2560 Aug 20 03:57:29 ubuntuhv
> >>> kernel: [  114.962711] hv_netvsc vmbus_0_14: Device MAC
> >>> 00:15:5d:6f:02:af link state up Aug 20 03:57:34 ubuntuhv kernel: [
> >>> 120.027718] hv_netvsc vmbus_0_14: net device safe to remove Aug 20
> >>> 03:57:34 ubuntuhv kernel: [  120.030047] hv_netvsc: hv_netvsc
> >>> channel opened successfully Aug 20 03:57:34 ubuntuhv kernel: [
> >>> 120.035422]
> >> hv_netvsc vmbus_0_14 eth0: unable to establish receive buffer's gpadl
> >> Aug
> >> 20 03:57:34 ubuntuhv kernel: [  120.039778] hv_netvsc vmbus_0_14 eth0:
> >> unable to connect to NetVSP - 4 Aug 20 03:57:34 ubuntuhv kernel: [
> >> 120.039818] ------------[ cut here ]------------ Aug 20 03:57:34 ubuntuhv
> kernel:
> >> [  120.039832] kernel BUG at drivers/hv/channel.c:504!
> >>
> >> This is one is also a rude BUG_ON:
> >>         ret = vmbus_post_msg(msg, sizeof(struct
> >> vmbus_channel_close_channel));
> >>
> >>         BUG_ON(ret != 0);
> >>
> >> vmbus_post_msg() hv_post_message() can easily return !0.
> >> i.e. if this kmalloc() fails:
> >>         addr = (unsigned long)kmalloc(sizeof(struct aligned_input),
> >> GFP_ATOMIC);
> >>         if (!addr)
> >>                 return -ENOMEM;
> >
> > I will submit a patch to handle this case. I suspect though that the
> > original ASSERT at channel.c (line 504) is not related to kmalloc failing in
> vmbus_post_msg(). I will also look at that issue as well.
> 
> I'm sure you can replace most BUG_ON() by a WARN_ON().
> Also print more details why the assertion does not hold.

The cases where I have intended to use BUG_ON are only cases where there was
reasonable way to roll back from the failure (barring bugs such as what we are discussing hre).
I will audit all BUG_ON calls and also print details to help debug.

Thank you,

K. Y  
> 
> Thanks,
> //richard
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