Messages in this thread Patch in this message | | | Date | Thu, 29 May 2014 12:33:42 -0300 | From | 'Arnaldo Carvalho de Melo' <> | Subject | [PATCH/RFC] Handle EFAULT in partial recvmmsg was Re: [PATCH/RFC] Re: recvmmsg() timeout behavior strangeness [RESEND] |
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Em Thu, May 29, 2014 at 11:17:05AM -0300, 'Arnaldo Carvalho de Melo' escreveu: > Em Thu, May 29, 2014 at 02:06:04PM +0000, David Laight escreveu: > > From: 'Arnaldo Carvalho de Melo' > > ... > > > > I remember some discussions from an XNET standards meeting (I've forgotten > > > > exactly which errors on which calls were being discussed). > > > > My recollection is that you return success with a partial transfer > > > > count for ANY error that happens after some data has been transferred. > > > > The actual error will be returned when it happens again on the next > > > > system call - Note the AGAIN, not a saved error.
> > > A saved error, for the right entity, in the recvmmsg case, that > > > basically is batching multiple recvmsg syscalls, doesn't sound like a > > > problem, i.e. the idea is to, as much as possible, mimic what multiple > > > recvmsg calls would do, but reduce its in/out kernel (and inside kernel > > > subsystems) overhead.
> > > Perhaps we can have something in between, i.e. for things like EFAULT, > > > we should report straight away, effectively dropping whatever datagrams > > > successfully received in the current batch, do you agree?
> > Not unreasonable - EFAULT shouldn't happen unless the application > > is buggy.
> Ok.
So the patch below should handle it, and record that the packets were dropped, not at the transport level, like UDP_MIB_INERRORS, for instance, would indicate, but at the batching, recvmmsg level, so perhaps we'll need a MIB variable for that.
Also a counterpart to the trace_kfree_skb(skb, udp_recvmsg) tracepoint for dropwatch and similar tools to use, Neil?
I'm keeping this separate from the timeout update patch.
- Arnaldo
diff --git a/net/socket.c b/net/socket.c index abf56b2a14f9..63491f015912 100644 --- a/net/socket.c +++ b/net/socket.c @@ -2415,13 +2415,17 @@ out_put: return datagrams; if (datagrams != 0) { + if (err == -EFAULT) { + atomic_add(datagrams, &sock->sk->sk_drops); + return -EFAULT; + } /* * We may return less entries than requested (vlen) if the * sock is non block and there aren't enough datagrams... */ if (err != -EAGAIN) { /* - * ... or if recvmsg returns an error after we + * ... or if recvmsg returns a socket error after we * received some datagrams, where we record the * error to return on the next call or if the * app asks about it using getsockopt(SO_ERROR).
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