linux-kernel - Re: 4.9.0 regression in pipe-backed iov

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Message-ID: <22648.41914.351371.678606@wylie.me.uk>
Date:   Fri, 13 Jan 2017 09:54:02 +0000
From:   "Alan J. Wylie" <alan@...ie.me.uk>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Thorsten Leemhuis <regressions@...mhuis.info>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: 4.9.0 regression in pipe-backed iov_iter with systemd-nspawn

at 09:33 on Fri 13-Jan-2017 Al Viro (viro@...IV.linux.org.uk) wrote:

> > 1735  splice(5, NULL, 1, NULL, 9223372036854775807, 0) = -1 EAGAIN (Resource temporarily unavailable)
> 
> Lovely...  So it was getting -EAGAIN all along.  Just in case - could you
> try the delta below and see if it triggers?  Simply to exclude the possibility
> that it *is* this call of splice() and the change has somehow buggered cleanup
> after the kernel_readv() failure...


$ git checkout linux-4.9.y
$ git apply patch1

$ uname -a
Linux frodo 4.9.3-dirty #1 SMP PREEMPT Fri Jan 13 09:44:42 GMT 2017 x86_64 AMD FX(tm)-8350 Eight-Core Processor AuthenticAMD GNU/Linux

# ps axfu | grep -A10 cron
root       987  0.0  0.0  18764  2128 ?        Ss   09:47   0:00 /usr/sbin/cron
root      1662  0.0  0.0  27340  2160 ?        S    09:51   0:00  \_ /usr/sbin/cron
root      1664  0.0  0.0   9840  1148 ?        Ss   09:51   0:00      \_ /bin/bash -c date; /work/chroot-shared/test.sh; date
root      1668  0.0  0.0   9840  2652 ?        S    09:51   0:00      |   \_ /bin/bash /work/chroot-shared/test.sh
root      1667  0.0  0.0  76156  5576 ?        S    09:51   0:00      \_ /usr/sbin/sendmail -FCronDaemon -odi -oem -oi -t
root      1669  0.0  0.0  76144  5412 ?        S    09:51   0:00          \_ /usr/sbin/postdrop -r

Another hang.

# dmesg  | tail
[   22.352442] r8169 0000:03:00.0: loading /lib/firmware/4.9.3-dirty/rtl_nic/rtl8168e-3.fw failed with error -2
[   22.408814] r8169 0000:03:00.0: direct-loading rtl_nic/rtl8168e-3.fw
[   22.408821] fw_set_page_data: fw-rtl_nic/rtl8168e-3.fw buf=ffff92b7b1cb8c80 data=ffffad1641179000 size=3872
[   22.536043] r8169 0000:03:00.0 enp3s0: link down
[   22.536079] r8169 0000:03:00.0 enp3s0: link down
[   24.873801] r8169 0000:03:00.0 enp3s0: link up
[   24.874766] br0: port 1(enp3s0) entered blocking state
[   24.876622] br0: port 1(enp3s0) entered forwarding state
[   24.878560] IPv6: ADDRCONF(NETDEV_CHANGE): br0: link becomes ready
[  219.683974] nr: 0->16, cur: 5->5, buffers: 16->16
# 

> 
> diff --git a/fs/splice.c b/fs/splice.c
> index 873d83104e79..1a2d1bc7f19e 100644
> --- a/fs/splice.c
> +++ b/fs/splice.c
> @@ -393,6 +393,9 @@ static ssize_t default_file_splice_read(struct file *in, loff_t *ppos,
>  	size_t offset, dummy, copied = 0;
>  	ssize_t res;
>  	int i;
> +	unsigned nrbufs = pipe->nrbufs,
> +		 curbuf = pipe->curbuf,
> +		 buffers = pipe->buffers;
>  
>  	if (pipe->nrbufs == pipe->buffers)
>  		return -EAGAIN;
> @@ -445,6 +448,16 @@ static ssize_t default_file_splice_read(struct file *in, loff_t *ppos,
>  		put_page(pages[i]);
>  	kvfree(pages);
>  	iov_iter_advance(&to, copied);	/* truncates and discards */
> +	if (res == -EAGAIN && (
> +		pipe->nrbufs != nrbufs ||
> +		pipe->curbuf != curbuf ||
> +		pipe->buffers != buffers)
> +	    ) {
> +		printk(KERN_ERR "nr: %d->%d, cur: %d->%d, buffers: %d->%d\n",
> +			nrbufs, pipe->nrbufs,
> +			curbuf, pipe->curbuf,
> +			buffers, pipe->buffers);
> +	}
>  	return res;
>  }
>  

-- 
Alan J. Wylie                                          http://www.wylie.me.uk/

Dance like no-one's watching. / Encrypt like everyone is.
Security is inversely proportional to convenience