On Mon, Oct 10, 2016 at 04:43:57AM +0100, Al Viro wrote:
> Very interesting. Could you slap something like
> diff --git a/lib/iov_iter.c b/lib/iov_iter.c
> index 0ce3411..1ef00e7 100644
> --- a/lib/iov_iter.c
> +++ b/lib/iov_iter.c
> @@ -682,8 +682,9 @@ static void pipe_advance(struct iov_iter *i, size_t size)
> {
> struct pipe_inode_info *pipe = i->pipe;
> struct pipe_buffer *buf;
> - int idx = i->idx;
> - size_t off = i->iov_offset;
> + int old_idx = idx = i->idx;
> + size_t old_off = off = i->iov_offset;
> + size_t old_size = size;
>
> if (unlikely(i->count < size))
> size = i->count;
> @@ -713,6 +714,9 @@ static void pipe_advance(struct iov_iter *i, size_t size)
> pipe->nrbufs--;
> }
> }
> + if (!sanity(i))
> + printk(KERN_ERR "buggered pipe_advance(%zd) [%d,%zd]",
> + old_size, old_idx, old_off);
> }
>
> void iov_iter_advance(struct iov_iter *i, size_t size)
>
> in there and try to reproduce that one?
My compiler choked on that, but I fixed it up. The printk didn't
trigger though..
idx = 0, offset = 0
curbuf = 0, nrbufs = 1, buffers = 16
[ffffffffb9a21100 ffffea00126019c0 0 4096]
[ (null) ffffea0013746440 0 0]
[ (null) ffffea00132956c0 0 0]
[ (null) ffffea0013295700 0 0]
[ (null) ffffea0013295740 0 0]
[ (null) ffffea0013295780 0 0]
[ (null) ffffea00132957c0 0 0]
[ (null) ffffea0013595c00 0 0]
[ (null) ffffea0012b1b6c0 0 0]
[ (null) (null) 0 0]
[ (null) (null) 0 0]
[ (null) (null) 0 0]
[ (null) (null) 0 0]
[ (null) (null) 0 0]
[ (null) (null) 0 0]
[ (null) (null) 0 0]
------------[ cut here ]------------
WARNING: CPU: 1 PID: 13581 at lib/iov_iter.c:327 sanity+0x102/0x150
CPU: 1 PID: 13581 Comm: trinity-c17 Not tainted 4.8.0-think+ #9
ffffc90000963ae8
ffffffffb93e22d1
0000000000000000
0000000000000000
ffffffffb9c1e1cb
ffffffffb93fa5b2
ffffc90000963b28
ffffffffb908b010
00000147d43c0e7f
ffffffffb9c1e1cb
0000000000000147
0000000000000010
Call Trace:
[<ffffffffb93e22d1>] dump_stack+0x6c/0x9b
[<ffffffffb93fa5b2>] ? sanity+0x102/0x150
[<ffffffffb908b010>] __warn+0x110/0x130
[<ffffffffb908b19c>] warn_slowpath_null+0x2c/0x40
[<ffffffffb93fa5b2>] sanity+0x102/0x150
[<ffffffffb93fe94e>] copy_page_to_iter+0x2be/0x480
[<ffffffffb91cc8b1>] ? workingset_activation+0xc1/0x120
[<ffffffffb91cc7f0>] ? workingset_refault+0x190/0x190
[<ffffffffb9195b85>] generic_file_read_iter+0x245/0xd30
[<ffffffffb92764ed>] generic_file_splice_read+0xfd/0x230
[<ffffffffb92763f0>] ? pipe_to_user+0x40/0x40
[<ffffffffb9275f08>] do_splice_to+0x98/0xd0
[<ffffffffb9276014>] splice_direct_to_actor+0xd4/0x2c0
[<ffffffffb9275660>] ? generic_pipe_buf_nosteal+0x10/0x10
[<ffffffffb92762c5>] do_splice_direct+0xc5/0x110
[<ffffffffb92381c2>] do_sendfile+0x242/0x470
[<ffffffffb923929d>] SyS_sendfile64+0x7d/0xf0
[<ffffffffb900279f>] do_syscall_64+0x7f/0x200
[<ffffffffb99de8cb>] entry_SYSCALL64_slow_path+0x25/0x25
---[ end trace 6773f425063b7f84 ]---
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