linux-kernel - Re: iov_iter

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Date:   Wed, 12 Apr 2017 12:27:09 -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 04:26:00PM +0100, Al Viro wrote:
 > On Wed, Apr 12, 2017 at 10:35:19AM -0400, Dave Jones wrote:
 > 
 > > [ 4140.040002] asked to read 8, claims to have read 4
 > > [ 4140.051634] actual size of data in pipe 8 
 > > [ 4140.063234] [0:8
 > 
 > > [ 4140.342955] ---[ end trace d074a8823fe244d4 ]---
 > > [ 4140.353868] in->f_op = ffffffffa02dc980, ->splice_write = ffffffff812b2c20
 > 
 > IOW, we just had someone's ->read_iter() return 4 after having deposited 8
 > bytes.  The next question is which file_operations had that been, whether
 > it was O_DIRECT or not and where in file had we been reading from...

[ 1010.008906] WARNING: CPU: 2 PID: 15216 at fs/splice.c:297 test_it+0x7d/0x120
[ 1010.021094] CPU: 2 PID: 15216 Comm: trinity-c5 Not tainted 4.11.0-rc6-think+ #13 
[ 1010.045849] Call Trace:
[ 1010.058136]  dump_stack+0x68/0x93
[ 1010.070379]  __warn+0xcb/0xf0
[ 1010.082473]  warn_slowpath_null+0x1d/0x20
[ 1010.094489]  test_it+0x7d/0x120
[ 1010.106443]  generic_file_splice_read+0x19a/0x1e0
[ 1010.118337]  do_splice_to+0x79/0x90
[ 1010.130161]  splice_direct_to_actor+0xc6/0x280
[ 1010.142032]  ? generic_pipe_buf_nosteal+0x10/0x10
[ 1010.153871]  do_splice_direct+0x9e/0xd0
[ 1010.165687]  do_sendfile+0x1d7/0x3c0
[ 1010.177442]  SyS_sendfile64+0x73/0xe0
[ 1010.189128]  do_syscall_64+0x66/0x1d0
[ 1010.200743]  entry_SYSCALL64_slow_path+0x25/0x25
[ 1010.212287] RIP: 0033:0x7f1bda69d0f9
[ 1010.223883] RSP: 002b:00007ffede478db8 EFLAGS: 00000246
[ 1010.235516]  ORIG_RAX: 0000000000000028
[ 1010.247115] RAX: ffffffffffffffda RBX: 0000000000000028 RCX: 00007f1bda69d0f9
[ 1010.258850] RDX: 00007f1bdac39000 RSI: 0000000000000186 RDI: 0000000000000186
[ 1010.270550] RBP: 00007f1bdad49000 R08: ffffe5d6e7f7c7f4 R09: 0000000092d54252
[ 1010.282174] R10: 0000000000200000 R11: 0000000000000246 R12: 0000000000000002
[ 1010.293781] R13: 00007f1bdad49048 R14: 00007f1bdad73ad8 R15: 00007f1bdad49000
[ 1010.305695] ---[ end trace 048fab9469c0948e ]---
[ 1010.317696] asked to read 2097152, claims to have read 7025
[ 1010.329471] actual size of data in pipe 65536 
[ 1010.341162] [0:4096
[ 1010.353232] ,1:4096
[ 1010.364402] ,2:4096
[ 1010.375608] ,3:4096
[ 1010.386346] ,4:4096
[ 1010.397027] ,5:4096
[ 1010.407611] ,6:4096
[ 1010.418010] ,7:4096
[ 1010.428533] ,8:4096
[ 1010.438885] ,9:4096
[ 1010.449269] ,10:4096
[ 1010.459462] ,11:4096
[ 1010.469519] ,12:4096
[ 1010.479326] ,13:4096
[ 1010.489093] ,14:4096
[ 1010.498711] ,15:4096
[ 1010.508217] ]
[ 1010.517570] f_op: ffffffffa0242980, f_flags: 311298, pos: 11/7036, size: 7036