On Mon, Aug 07, 2017 at 04:18:18PM -0400, Dave Jones wrote:
> On Fri, Apr 28, 2017 at 06:20:25PM +0100, Al Viro wrote:
> > On Fri, Apr 28, 2017 at 12:50:24PM -0400, Dave Jones wrote:
> > > currently running v4.11-rc8-75-gf83246089ca0
> > >
> > > sunrpc bit is for the other unrelated problem I'm chasing.
> > >
> > > note also, I saw the backtrace without the fs/splice.c changes.
> >
> > Interesting... Could you add this and see if that triggers?
> >
> > diff --git a/fs/splice.c b/fs/splice.c
> > index 540c4a44756c..12a12d9c313f 100644
> > --- a/fs/splice.c
> > +++ b/fs/splice.c
> > @@ -306,6 +306,9 @@ ssize_t generic_file_splice_read(struct file *in, loff_t *ppos,
> > kiocb.ki_pos = *ppos;
> > ret = call_read_iter(in, &kiocb, &to);
> > if (ret > 0) {
> > + if (WARN_ON(iov_iter_count(&to) != len - ret))
> > + printk(KERN_ERR "ops %p: was %zd, left %zd, returned %d\n",
> > + in->f_op, len, iov_iter_count(&to), ret);
> > *ppos = kiocb.ki_pos;
> > file_accessed(in);
> > } else if (ret < 0) {
>
> Hey Al,
> Due to a git stash screw up on my part, I've had this leftover WARN_ON
> in my tree for the last couple months. (That screw-up might turn out to be
> serendipitous if this is a real bug..)
>
> Today I decided to change things up and beat up on xfs for a change, and
> was able to trigger this again.
>
> Is this check no longer valid, or am I triggering the same bug we were chased
> down in nfs, but now in xfs ? (None of the other detritus from that debugging
> back in April made it, just those three lines above).
Revisiting this. I went back and dug out some of the other debug diffs [1]
from that old thread.
I can easily trigger this spew on xfs.
WARNING: CPU: 1 PID: 2251 at fs/splice.c:292 test_it+0xd4/0x1d0
CPU: 1 PID: 2251 Comm: trinity-c42 Not tainted 4.13.0-rc7-think+ #1
task: ffff880459173a40 task.stack: ffff88044f7d0000
RIP: 0010:test_it+0xd4/0x1d0
RSP: 0018:ffff88044f7d7878 EFLAGS: 00010283
RAX: 0000000000000000 RBX: ffff88044f44b968 RCX: ffffffff81511ea0
RDX: 0000000000000003 RSI: dffffc0000000000 RDI: ffff88044f44ba68
RBP: ffff88044f7d78c8 R08: ffff88046b218ec0 R09: 0000000000000000
R10: ffff88044f7d7518 R11: 0000000000000000 R12: 0000000000001000
R13: 0000000000000001 R14: 00000000ffffffff R15: 0000000000000001
FS: 00007fdbc09b2700(0000) GS:ffff88046b200000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 0000000459e1d000 CR4: 00000000001406e0
Call Trace:
generic_file_splice_read+0x414/0x4e0
? opipe_prep.part.14+0x180/0x180
? lockdep_init_map+0xb2/0x2b0
? rw_verify_area+0x65/0x150
do_splice_to+0xab/0xc0
splice_direct_to_actor+0x1f5/0x540
? generic_pipe_buf_nosteal+0x10/0x10
? do_splice_to+0xc0/0xc0
? rw_verify_area+0x9d/0x150
do_splice_direct+0x1b9/0x230
? splice_direct_to_actor+0x540/0x540
? __sb_start_write+0x164/0x1c0
? do_sendfile+0x7b3/0x840
do_sendfile+0x428/0x840
? do_compat_pwritev64+0xb0/0xb0
? __might_sleep+0x72/0xe0
? kasan_check_write+0x14/0x20
SyS_sendfile64+0xa4/0x120
? SyS_sendfile+0x150/0x150
? mark_held_locks+0x23/0xb0
? do_syscall_64+0xc0/0x3e0
? SyS_sendfile+0x150/0x150
do_syscall_64+0x1bc/0x3e0
? syscall_return_slowpath+0x240/0x240
? mark_held_locks+0x23/0xb0
? return_from_SYSCALL_64+0x2d/0x7a
? trace_hardirqs_on_caller+0x182/0x260
? trace_hardirqs_on_thunk+0x1a/0x1c
entry_SYSCALL64_slow_path+0x25/0x25
RIP: 0033:0x7fdbc02dd219
RSP: 002b:00007ffc5024fa48 EFLAGS: 00000246
ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 0000000000000028 RCX: 00007fdbc02dd219
RDX: 00007fdbbe348000 RSI: 0000000000000011 RDI: 0000000000000015
RBP: 00007ffc5024faf0 R08: 000000000000006d R09: 0094e82f2c730a50
R10: 0000000000001000 R11: 0000000000000246 R12: 0000000000000002
R13: 00007fdbc0885058 R14: 00007fdbc09b2698 R15: 00007fdbc0885000
---[ end trace a5847ef0f7be7e20 ]---
asked to read 4096, claims to have read 1
actual size of data in pipe 4096
[0:4096]
f_op: ffffffffa058c920, f_flags: 49154, pos: 0/1, size: 0
I'm still trying to narrow down an exact reproducer, but it seems having
trinity do a combination of sendfile & writev, with pipes and regular
files as fd's is the best repro.
Is this a real problem, or am I chasing ghosts ? That it doesn't happen
on ext4 or btrfs is making me wonder...
Dave
[1] https://lkml.org/lkml/2017/4/11/921
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