Re: [LKP] [fs/namei.c] e013ec23b8: WARNING:at_fs/dcache.c:#dentry_free

[Oliver Sang]

On Wed, Sep 04, 2019 at 02:52:40PM +0800, Oliver Sang wrote:
> On Sat, Aug 31, 2019 at 04:42:46PM +0100, Al Viro wrote:
> > On Sat, Aug 31, 2019 at 09:09:17PM +0800, kernel test robot wrote:
> > 
> > > [   13.886602] WARNING: CPU: 0 PID: 541 at fs/dcache.c:338 dentry_free+0x7f/0x90
> > > [   13.889208] Modules linked in:
> > > [   13.890276] CPU: 0 PID: 541 Comm: readlink Not tainted 5.3.0-rc1-00008-ge013ec23b8231 #1
> > > [   13.892699] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014
> > > [   13.895419] RIP: 0010:dentry_free+0x7f/0x90
> > > [   13.896739] Code: f0 75 cb 48 8d be b0 00 00 00 48 83 c4 08 48 c7 c6 60 8d cd a5 e9 51 69 e4 ff 48 89 3c 24 48 c7 c7 f8 a9 cb a6 e8 7f 37 e3 ff <0f> 0b 48 8b 34 24 eb 8f 66 0f 1f 84 00 00 00 00 00 66 66 66 66 90
> > > [   13.901957] RSP: 0018:ffffb5524063fe38 EFLAGS: 00010282
> > > [   13.903527] RAX: 0000000000000024 RBX: ffff9941878040c0 RCX: ffffffffa706aa08
> > > [   13.905566] RDX: 0000000000000000 RSI: 0000000000000096 RDI: 0000000000000246
> > > [   13.907612] RBP: 0000000000000000 R08: 0000000000000280 R09: 0000000000000033
> > > [   13.909664] R10: 0000000000000000 R11: ffffb5524063fce8 R12: ffff994187804118
> > > [   13.911711] R13: ffff99427a810000 R14: ffff994187d7c8f0 R15: ffff99427a810b80
> > > [   13.913753] FS:  0000000000000000(0000) GS:ffff9942bfc00000(0000) knlGS:0000000000000000
> > > [   13.916187] CS:  0010 DS: 002b ES: 002b CR0: 0000000080050033
> > > [   13.917892] CR2: 000000000937458b CR3: 000000006800a000 CR4: 00000000000006f0
> > > [   13.919925] Call Trace:
> > > [   13.920840]  __dentry_kill+0x13c/0x1a0
> > > [   13.922076]  path_put+0x12/0x20
> > > [   13.923148]  free_fs_struct+0x1b/0x30
> > > [   13.924346]  do_exit+0x304/0xc40
> > > [   13.925438]  ? __schedule+0x25d/0x670
> > > [   13.926642]  do_group_exit+0x3a/0xa0
> > > [   13.927817]  __ia32_sys_exit_group+0x14/0x20
> > > [   13.929160]  do_fast_syscall_32+0xa9/0x340
> > > [   13.930565]  entry_SYSENTER_compat+0x7f/0x91
> > > [   13.931924] ---[ end trace 02c6706eb2c2ebf2 ]---
> > > 
> > > 
> > > To reproduce:
> > > 
> > >         # build kernel
> > > 	cd linux
> > > 	cp config-5.3.0-rc1-00008-ge013ec23b8231 .config
> > > 	make HOSTCC=gcc-7 CC=gcc-7 ARCH=x86_64 olddefconfig prepare modules_prepare bzImage
> > > 
> > >         git clone https://github.com/intel/lkp-tests.git
> > >         cd lkp-tests
> > >         bin/lkp qemu -k <bzImage> job-script # job-script is attached in this email
> > 
> > Can't reproduce here...
> 
> any detail failure by using this reproducer?
> 
> > 
> > I see one potential problem in there, but I would expect it to have the
> > opposite effect (I really don't believe that it's a ->d_count wraparound -
> > that would've taken much longer than a minute, if nothing else).
> > 
> > How reliably is it reproduced on your setup and does the following have
> > any impact, one way or another?
> 
> It is always reproduced. We noticed that your branch was rebased. If it's still with problem, will let you know.

by testing the below HEAD commit of current branch, the issue gone

commit 46c46f8df9aa425cc4d6bc89d57a6fedf83dc797 (HEAD -> work.namei, origin/work.namei)
Author: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Date:   Sat Jul 27 16:29:22 2019 -0400

> 
> > 
> > diff --git a/fs/namei.c b/fs/namei.c
> > index 412479e4c258..671c3c1a3425 100644
> > --- a/fs/namei.c
> > +++ b/fs/namei.c
> > @@ -643,10 +643,8 @@ static bool legitimize_root(struct nameidata *nd)
> >  {
> >  	if (!nd->root.mnt || (nd->flags & LOOKUP_ROOT))
> >  		return true;
> > -	if (unlikely(!legitimize_path(nd, &nd->root, nd->root_seq)))
> > -		return false;
> >  	nd->flags |= LOOKUP_ROOT_GRABBED;
> > -	return true;
> > +	return legitimize_path(nd, &nd->root, nd->root_seq);
> >  }
> >  
> >  /*
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