linux-kernel - Re: iov_iter

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Date:   Tue, 11 Apr 2017 22:29:11 -0400
From:   Dave Jones <davej@...emonkey.org.uk>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: iov_iter_pipe warning.

On Wed, Apr 12, 2017 at 02:15:32AM +0100, Al Viro wrote:
 > On Tue, Apr 11, 2017 at 08:58:53PM -0400, Dave Jones wrote:
 > > [  462.696557] in->f_op = ffffffffa02df980, ->splice_write = ffffffff812b2b20
 > > $ grep ffffffffa02df980 /proc/kallsyms 
 > > ffffffffa02df980 r nfs4_file_operations	[nfsv4]
 > > $ grep ffffffff812b2b20 /proc/kallsyms 
 > > ffffffff812b2b20 T iter_file_splice_write
 > 
 > Let's try to figure out whether it's read or write side going wrong.
 > 
 > diff --git a/fs/splice.c b/fs/splice.c
 > index 006ba50f4ece..0a7c0bd3e164 100644
 > --- a/fs/splice.c
 > +++ b/fs/splice.c
 > @@ -970,10 +970,26 @@ ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
 >  	while (len) {
 >  		size_t read_len;
 >  		loff_t pos = sd->pos, prev_pos = pos;
 > +		if (WARN_ON(pipe->nrbufs)) {
 > +			printk(KERN_ERR "in->f_op = %p, ->splice_write = %p\n",
 > +				in->f_op,
 > +				sd->u.file->f_op->splice_write);
 > +		}
 >  
 >  		ret = do_splice_to(in, &pos, pipe, len, flags);
 >  		if (unlikely(ret <= 0))
 >  			goto out_release;
 > +		{
 > +			int idx = pipe->curbuf;
 > +			int n = pipe->nrbufs;
 > +			size_t size = 0;
 > +			while (n--) {
 > +				size += pipe->bufs[idx++].len;
 > +				if (idx == pipe->buffers)
 > +					idx = 0;
 > +			}
 > +			WARN_ON(size != ret);
 > +		}
 >  
 >  		read_len = ret;
 >  		sd->total_len = read_len;

WARNING: CPU: 0 PID: 21500 at fs/splice.c:985 splice_direct_to_actor+0x13f/0x280
CPU: 0 PID: 21500 Comm: trinity-c4 Not tainted 4.11.0-rc6-think+ #10 
Call Trace:
 dump_stack+0x68/0x93
 __warn+0xcb/0xf0
 warn_slowpath_null+0x1d/0x20
 splice_direct_to_actor+0x13f/0x280
 ? generic_pipe_buf_nosteal+0x10/0x10
 do_splice_direct+0x9e/0xd0
 do_sendfile+0x1d7/0x3c0
 SyS_sendfile64+0x73/0xe0
 do_syscall_64+0x66/0x1d0
 entry_SYSCALL64_slow_path+0x25/0x25
RIP: 0033:0x7febc78b30f9
RSP: 002b:00007ffd767b6398 EFLAGS: 00000246
  ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 0000000000000028 RCX: 00007febc78b30f9
RDX: 00007febc5c1e000 RSI: 0000000000000130 RDI: 0000000000000130
RBP: 00007febc7f66000 R08: 0000000000000ff1 R09: fffffffffffffffd
R10: 0000000000000008 R11: 0000000000000246 R12: 0000000000000002
R13: 00007febc7f66048 R14: 00007febc7f89ad8 R15: 00007febc7f66000
---[ end trace d002d06d5879c8a9 ]---
in->f_op = ffffffffa02df980, ->splice_write = ffffffff812b2b20

This time around it locked up completely. Weird.

	Dave