Date: Thu, 19 Jan 2017 22:55:01 +0000 From: Rick Macklem <rmacklem@uoguelph.ca> To: FreeBSD Net <freebsd-net@freebsd.org> Subject: Re: sosend returning ERESTART Message-ID: <YTXPR01MB01890EF52EB851BE60C2384ADD7E0@YTXPR01MB0189.CANPRD01.PROD.OUTLOOK.COM> In-Reply-To: <YTXPR01MB01897EB23D86F8ADADD94F85DD7E0@YTXPR01MB0189.CANPRD01.PROD.OUTLOOK.COM> References: <01000159aac969e6-b2fc3913-d04e-42d4-befd-402ed0d830bf-000000@email.amazonses.com> <20170117100634.GS2349@kib.kiev.ua> <01000159afddb7ce-064a5d17-4b81-4b2c-a9b4-3ddd2ad2e377-000000@email.amazonses.com> <20170118103650.GE2349@kib.kiev.ua> <01000159b390c409-5adcb488-67e8-4038-b9b0-5d4f33460205-000000@email.amazonses.com> <YTXPR01MB018941314216E668972D7FCADD7F0@YTXPR01MB0189.CANPRD01.PROD.OUTLOOK.COM>, <20170119073424.GM2349@kib.kiev.ua>, <YTXPR01MB01897EB23D86F8ADADD94F85DD7E0@YTXPR01MB0189.CANPRD01.PROD.OUTLOOK.COM>
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Konstantin Belousov wrote:
>On Wed, Jan 18, 2017 at 10:52:02PM +0000, Rick Macklem wrote:
>> Colin Percival wrote:
>> >On 01/18/17 02:36, Konstantin Belousov wrote:
>> >> On Wed, Jan 18, 2017 at 04:37:40AM +0000, Colin Percival wrote:
>> >>> Thanks, looks like that was exactly it -- if the TCP send buffer was=
full
>> >>> we would call sbwait, and if a signal arrived it would return ERESTA=
RT.
>> >>> It looks like setting the SB_NOINTR flag will prevent this; I'm test=
ing a
>> >>> patch right now.
>> >>
>> >> Note that passing SB_NOINTR unconditionally or even only for mounts
>> >> with nointr (default) option is wrong. You make the socket operation
>> >> uninterruptible, process terminate-ability becomes depended on the
>> >> external factor, the behaviour of the remote system.
>> >
>> >I'm not sure what you're getting at here. The fact that "NFS mounted w=
ithout
>> >the intr flag" + "unresponsive NFS server" =3D "unkillable processes" h=
as been
>> >a (mis)feature of NFS for decades.
>> The case I would like to see work is the forced dismount. I need to go l=
ook at
>> what it does and see if SB_NOINTR would break it worse than it is broken=
now.
>> (It is currently broken when something like "umount" without -f is done,=
which
>> locks up the mounted on vnode so "umount -f" never gets to the umount(2=
) syscall.
>> I do plan on a "straight ot NFS" option for umount(8) to avoid this pro=
blem, but
>> haven't gotten around to it.)
>>
>> The alternative to SB_NOINTR is looping and doing the sosend() again for=
the
>> case where it returns ERESTART and "intr" wasn't set on the mount.
>Note that the condition of pending signal which triggered ERESTART is
>permanent until the signal is delivered or blocked. In other words, or
>future PCATCH sleeps will fail with ERESTART/EINTR.
Right. But presumably if the TCP connection is still working, a subsequent
attempt will not have to sleep in sblock() or sbwait() in sosend() and will
succeed?
I think Colin was already testing this looping version before SB_NOINTR and
found it worked well for his case.
--> I think this does imply that it should only loop N times and then give =
up
and reply RPC_CANTSEND (which is what it does the first time now).
- The RPC_CANTSEND is what triggers the client to create a new TCP co=
nnection
and this is what causes grief for his mounts against the AmazonEFS =
server
(which is broken because the new TCP connection often results in a
NFS4ERR_BAD_SESSION which should not happen.)
Colin, have you tested the "loop on ERESTART" version of the patch?
And maybe you could add a loop counter to limit the number of iterations?
rick
[stuff snipped]
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