From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751309AbdH1Ube (ORCPT ); Mon, 28 Aug 2017 16:31:34 -0400 Received: from scorn.kernelslacker.org ([45.56.101.199]:40660 "EHLO scorn.kernelslacker.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750841AbdH1Ubc (ORCPT ); Mon, 28 Aug 2017 16:31:32 -0400 Date: Mon, 28 Aug 2017 16:31:30 -0400 From: Dave Jones To: Al Viro , Linux Kernel Cc: linux-xfs@vger.kernel.org Subject: Re: iov_iter_pipe warning. Message-ID: <20170828203130.y6dq5fqovev6wmrv@codemonkey.org.uk> Mail-Followup-To: Dave Jones , Al Viro , Linux Kernel , linux-xfs@vger.kernel.org References: <20170412152600.GP29622@ZenIV.linux.org.uk> <20170412162709.bn5qfk4seues3yos@codemonkey.org.uk> <20170412170723.GQ29622@ZenIV.linux.org.uk> <20170412190318.srkkdytf2ebrjzrg@codemonkey.org.uk> <20170421175430.GT29622@ZenIV.linux.org.uk> <20170428152955.mafs3f22srmm34aw@codemonkey.org.uk> <20170428164313.GK29622@ZenIV.linux.org.uk> <20170428165024.ofyl2atpjwohekqa@codemonkey.org.uk> <20170428172024.GL29622@ZenIV.linux.org.uk> <20170807201818.kykqzexce6ap6aik@codemonkey.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170807201818.kykqzexce6ap6aik@codemonkey.org.uk> User-Agent: NeoMutt/20170609 (1.8.3) X-Spam-Note: SpamAssassin invocation failed Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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