On 11/27/2018 07:34 AM, Andrew Morton wrote:
On Fri, 16 Nov 2018 15:12:48 +0800 Li Zhijian <lizhij...@cn.fujitsu.com> wrote:

Previously, sys_link() will fail due to the new path is already existed.
this case ofen appears when we use a concated initrd, below is an
sample:

1) prepare a basic rootfs, it contains a regular files rc.local
lizhijian@:~/yocto-tiny-i386-2016-04-22$ cat etc/rc.local
  #!/bin/sh
  echo "Running /etc/rc.local..."
yocto-tiny-i386-2016-04-22$ find . | sed 's,^\./,,' | cpio -o -H newc | gzip -n -9 
>../rootfs.cgz

2) create a extra initrd which also includes a etc/rc.local
lizhijian@:~/lkp-x86_64/etc$ echo "append initrd" >rc.local
lizhijian@:~/lkp/lkp-x86_64/etc$ cat rc.local
append initrd
lizhijian@:~/lkp/lkp-x86_64/etc$ ln rc.local rc.local.hardlink
append initrd
lizhijian@:~/lkp/lkp-x86_64/etc$ stat rc.local rc.local.hardlink
   File: 'rc.local'
   Size: 14             Blocks: 8          IO Block: 4096   regular file
Device: 801h/2049d      Inode: 11296086    Links: 2
Access: (0664/-rw-rw-r--)  Uid: ( 1002/lizhijian)   Gid: ( 1002/lizhijian)
Access: 2018-11-15 16:08:28.654464815 +0800
Modify: 2018-11-15 16:07:57.514903210 +0800
Change: 2018-11-15 16:08:24.180228872 +0800
  Birth: -
   File: 'rc.local.hardlink'
   Size: 14             Blocks: 8          IO Block: 4096   regular file
Device: 801h/2049d      Inode: 11296086    Links: 2
Access: (0664/-rw-rw-r--)  Uid: ( 1002/lizhijian)   Gid: ( 1002/lizhijian)
Access: 2018-11-15 16:08:28.654464815 +0800
Modify: 2018-11-15 16:07:57.514903210 +0800
Change: 2018-11-15 16:08:24.180228872 +0800
  Birth: -

lizhijian@:~/lkp/lkp-x86_64$ find . | sed 's,^\./,,' | cpio -o -H newc | gzip -n 
-9 >../rc-local.cgz
lizhijian@:~/lkp/lkp-x86_64$ gzip -dc ../rc-local.cgz | cpio -t
.
etc
etc/rc.local.hardlink <<< it will be extracted first at this initrd
etc/rc.local

3) concate 2 initrds and boot
lizhijian@:~/lkp$ cat rootfs.cgz rc-local.cgz >concate-initrd.cgz
lizhijian@:~/lkp$ qemu-system-x86_64 -nographic -enable-kvm -cpu host -smp 1 -m 1024 
-kernel ~/lkp/linux/arch/x86/boot/bzImage -append "console=ttyS0 earlyprint=ttyS0 
ignore_loglevel" -initrd ./concate-initr.cgz -serial stdio -nodefaults

In this case, sys_link(2) will fail and return -EEXIST, so we can only
get the rc.local at rootfs.cgz instead of rc-local.cgz
I can't claim to understand this, but I believe you ;)

thank you.

IMO, people who use concatenated initrd(cat rootfs.cgz rc-local.cgz 
>concatenated-initrd.cgz),
could expect that the later initrd(rc-local.cgz) can overwrite the previous 
initrd(rootfs.cgz).

However the previous kernel can not ensure this.


How serious is this problem?  Do you think a 4.20 merge is justified?

It's critical for our scenario where it always concatenates multiple initrds.
and our scenario often use the latest kernel, so 4.20+ is good to us.



Or a -stable backport?  If so, why?

The forward declaration is unpleasing.  Why not simply move the function?

Got it, i will update in V2


Thanks


--- a/init/initramfs.c~initramfs-clean-old-path-before-creating-a-hardlink-fix
+++ a/init/initramfs.c
@@ -291,7 +291,17 @@ static int __init do_reset(void)
        return 1;
  }
-static void __init clean_path(char *path, umode_t fmode);
+static void __init clean_path(char *path, umode_t fmode)
+{
+       struct kstat st;
+
+       if (!vfs_lstat(path, &st) && (st.mode ^ fmode) & S_IFMT) {
+               if (S_ISDIR(st.mode))
+                       ksys_rmdir(path);
+               else
+                       ksys_unlink(path);
+       }
+}
static int __init maybe_link(void)
  {
@@ -305,18 +315,6 @@ static int __init maybe_link(void)
        return 0;
  }
-static void __init clean_path(char *path, umode_t fmode)
-{
-       struct kstat st;
-
-       if (!vfs_lstat(path, &st) && (st.mode ^ fmode) & S_IFMT) {
-               if (S_ISDIR(st.mode))
-                       ksys_rmdir(path);
-               else
-                       ksys_unlink(path);
-       }
-}
-
  static __initdata int wfd;
static int __init do_name(void)
_



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