linux-kernel - Re: [regression?] distcc says: (dcc_pump_sendfile) ERROR: sendfile returned 0? can't cope (bisected)

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Date:	Thu, 08 May 2008 23:22:19 -0500
From:	Tom Zanussi <zanussi@...cast.net>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Dan Williams <dan.j.williams@...el.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [regression?] distcc says: (dcc_pump_sendfile) ERROR: sendfile
	returned 0? can't cope (bisected)


On Thu, 2008-05-08 at 02:21 -0500, Tom Zanussi wrote:
> On Wed, 2008-05-07 at 23:16 +0200, Jens Axboe wrote:
> > On Wed, May 07 2008, Dan Williams wrote:
> > > Hi Tom, Jens,
> > > 
> > > My build system started reporting these error messages recently.
> > > Reverting commit c3270e577c18b3d0e984c3371493205a4807db9d on top of
> > > 2.6.26-rc1 gets things working for me again.
> > 
> > Irk, that patch did scare me a bit (hence I asked Tom to double check as
> > wel :-). I'll take a look in the morning, all test boxes are off at this
> > point in time.
> > 
> 
> I did, and it still looks ok to me, but obviously it's not, so I'll have
> to do some more digging.
> 
> The only thing I can think of right now that might be a possible cause
> would be in splice_direct_to_actor(), if we had an incomplete transfer,
> the sd->pos returned and assigned would have the value set by the failed
> actor().  Maybe something like the following would take care of that
> case, but I haven't had a chance to test it yet - will do that tomorrow
> night...
> 

Looks like I was on the right track - can you try this patch out
instead?  It makes sure sd.pos is updated correctly if the transfer was
incomplete or failed.  I ran some kernel compiles using distcc while
running blktrace in sendfile mode and didn't see any problems with
either.

Tom

diff --git a/fs/splice.c b/fs/splice.c
index 633f58e..3bd95a7 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -986,7 +986,7 @@ ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
 
 	while (len) {
 		size_t read_len;
-		loff_t pos = sd->pos;
+		loff_t pos = sd->pos, prev_pos = pos;
 
 		ret = do_splice_to(in, &pos, pipe, len, flags);
 		if (unlikely(ret <= 0))
@@ -1001,15 +1001,19 @@ ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
 		 * could get stuck data in the internal pipe:
 		 */
 		ret = actor(pipe, sd);
-		if (unlikely(ret <= 0))
+		if (unlikely(ret <= 0)) {
+			sd->pos = prev_pos;
 			goto out_release;
+		}
 
 		bytes += ret;
 		len -= ret;
 		sd->pos = pos;
 
-		if (ret < read_len)
+		if (ret < read_len) {
+			sd->pos = prev_pos + ret;
 			goto out_release;
+		}
 	}
 
 done:


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