Re: [RFC PATCH 16/35] ovl: readd lsattr/chattr support

From: Amir Goldstein
Date: Tue Apr 17 2018 - 15:51:09 EST

On Thu, Apr 12, 2018 at 6:08 PM, Miklos Szeredi <mszeredi@xxxxxxxxxx> wrote:
> Implement FS_IOC_GETFLAGS and FS_IOC_SETFLAGS.
>
> Needs vfs_ioctl() exported to modules.
>
> Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
> ---
> fs/internal.h | 1 -
> fs/ioctl.c | 1 +
> fs/overlayfs/file.c | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++++
> include/linux/fs.h | 2 ++
> 4 files changed, 62 insertions(+), 1 deletion(-)
>
> diff --git a/fs/internal.h b/fs/internal.h
> index 3319bf39e339..d5108d9c6a2f 100644
> --- a/fs/internal.h
> +++ b/fs/internal.h
> @@ -176,7 +176,6 @@ extern const struct dentry_operations ns_dentry_operations;
> */
> extern int do_vfs_ioctl(struct file *file, unsigned int fd, unsigned int cmd,
> unsigned long arg);
> -extern long vfs_ioctl(struct file *file, unsigned int cmd, unsigned long arg);
>
> /*
> * iomap support:
> diff --git a/fs/ioctl.c b/fs/ioctl.c
> index 5ace7efb0d04..696f4c46a868 100644
> --- a/fs/ioctl.c
> +++ b/fs/ioctl.c
> @@ -49,6 +49,7 @@ long vfs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> out:
> return error;
> }
> +EXPORT_SYMBOL(vfs_ioctl);
>
> static int ioctl_fibmap(struct file *filp, int __user *p)
> {
> diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
> index 05e3e2f80b89..cc004ff1b05b 100644
> --- a/fs/overlayfs/file.c
> +++ b/fs/overlayfs/file.c
> @@ -8,6 +8,7 @@
>
> #include <linux/cred.h>
> #include <linux/file.h>
> +#include <linux/mount.h>
> #include <linux/xattr.h>
> #include <linux/uio.h>
> #include "overlayfs.h"
> @@ -291,6 +292,63 @@ long ovl_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
> return ret;
> }
>
> +static long ovl_real_ioctl(struct file *file, unsigned int cmd,
> + unsigned long arg)
> +{
> + struct fd real;
> + const struct cred *old_cred;
> + long ret;
> +
> + ret = ovl_real_file(file, &real);
> + if (ret)
> + return ret;
> +
> + old_cred = ovl_override_creds(file_inode(file)->i_sb);
> + ret = vfs_ioctl(real.file, cmd, arg);
> + revert_creds(old_cred);
> +
> + fdput(real);
> +
> + return ret;
> +}
> +
> +long ovl_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> +{
> + long ret;
> + struct inode *inode = file_inode(file);
> +
> + switch (cmd) {
> + case FS_IOC_GETFLAGS:
> + ret = ovl_real_ioctl(file, cmd, arg);
> + break;
> +
> + case FS_IOC_SETFLAGS:
> + if (!inode_owner_or_capable(inode))
> + return -EACCES;
> +
> + ret = mnt_want_write_file(file);
> + if (ret)
> + return ret;
> +
> + ret = ovl_copy_up(file_dentry(file));
> + if (!ret) {
> + ret = ovl_real_ioctl(file, cmd, arg);
> +

I got this lockdep splat with overlayfs-rorw and overlay/040, but I don't
see the problem in the patch:

overlay/040 [19:29:01][ 7.414427]
[ 7.415349] ============================================
[ 7.417863] WARNING: possible recursive locking detected
[ 7.419652] 4.16.0-rc7-xfstests-00054-g1b18a246f764-dirty #3233 Not tainted
[ 7.421517] --------------------------------------------
[ 7.422736] chattr/2376 is trying to acquire lock:
[ 7.423843] (sb_writers#10){.+.+}, at: [<000000003170ac81>]
mnt_want_write_file+0x21/0x4a
[ 7.425683]
[ 7.425683] but task is already holding lock:
[ 7.427397] (sb_writers#10){.+.+}, at: [<000000003170ac81>]
mnt_want_write_file+0x21/0x4a
[ 7.430180]
[ 7.430180] other info that might help us debug this:
[ 7.432511] Possible unsafe locking scenario:
[ 7.432511]
[ 7.433860] CPU0
[ 7.434424] ----
[ 7.434987] lock(sb_writers#10);
[ 7.435768] lock(sb_writers#10);
[ 7.436692]
[ 7.436692] *** DEADLOCK ***
[ 7.436692]
[ 7.438460] May be due to missing lock nesting notation
[ 7.438460]
[ 7.440477] 1 lock held by chattr/2376:
[ 7.441876] #0: (sb_writers#10){.+.+}, at: [<000000003170ac81>]
mnt_want_write_file+0x21/0x4a
[ 7.444537]
[ 7.444537] stack backtrace:
[ 7.445881] CPU: 1 PID: 2376 Comm: chattr Not tainted
4.16.0-rc7-xfstests-00054-g1b18a246f764-dirty #3233
[ 7.449594] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS Ubuntu-1.8.2-1ubuntu1 04/01/2014
[ 7.453121] Call Trace:
[ 7.453945] dump_stack+0x7c/0xb2
[ 7.454957] validate_chain.isra.24+0x6da/0x8af
[ 7.456341] __lock_acquire+0x5e6/0x67b
[ 7.457643] ? __lock_acquire+0x5e6/0x67b
[ 7.458879] lock_acquire+0x139/0x1dd
[ 7.459988] ? mnt_want_write_file+0x21/0x4a
[ 7.461317] __sb_start_write+0x91/0x163
[ 7.462500] ? mnt_want_write_file+0x21/0x4a
[ 7.463822] mnt_want_write_file+0x21/0x4a
[ 7.465091] xfs_ioc_setxflags+0x70/0xe5
[ 7.466266] xfs_file_ioctl+0x4a7/0xa90
[ 7.467452] ? __lock_acquire+0x5e6/0x67b
[ 7.468681] ? terminate_walk+0x20/0xd9
[ 7.469835] ? __lock_is_held+0x40/0x71
[ 7.471012] vfs_ioctl+0x1e/0x2b
[ 7.472008] ovl_real_ioctl+0x45/0x71
[ 7.473122] ovl_ioctl+0x9a/0xf2
[ 7.474114] vfs_ioctl+0x1e/0x2b
[ 7.475149] do_vfs_ioctl+0x579/0x5f1
[ 7.476341] ? entry_SYSCALL_64_after_hwframe+0x52/0xb7
[ 7.477765] SyS_ioctl+0x52/0x74
[ 7.479041] do_syscall_64+0x76/0x182
[ 7.480419] entry_SYSCALL_64_after_hwframe+0x42/0xb7
[ 7.482536] RIP: 0033:0x7fde8d270dd7
[ 7.483919] RSP: 002b:00007ffde2ae7e98 EFLAGS: 00000246 ORIG_RAX:
0000000000000010
[ 7.486862] RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007fde8d270dd7
[ 7.489554] RDX: 00007ffde2ae7eac RSI: 0000000040086602 RDI: 0000000000000003
[ 7.492227] RBP: 0000000000000010 R08: 0000000000000000 R09: 0000000000000001
[ 7.494922] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
[ 7.497642] R13: 00007ffde2ae81a0 R14: 00007ffde2ae8188 R15: 0000000000000000
[ 7.540886] XFS (vdf): Mounting V5 Filesystem
[ 7.563795] XFS (vdf): Ending clean mount

Thanks,
Amir.