Re: [PATCH] fsnotify: fix unlink performance regression

[Amir Goldstein <amir73il@gmail.com>]

On Sun, May 5, 2019 at 7:34 PM kbuild test robot <lkp@intel.com> wrote:
>
> Hi Amir,
>
> I love your patch! Yet something to improve:
>
> [auto build test ERROR on linus/master]
> [also build test ERROR on v5.1-rc7 next-20190503]
> [if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
>
> url:    https://github.com/0day-ci/linux/commits/Amir-Goldstein/fsnotify-fix-unlink-performance-regression/20190505-233115
> config: riscv-tinyconfig (attached as .config)
> compiler: riscv64-linux-gcc (GCC) 8.1.0
> reproduce:
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # save the attached .config to linux build tree
>         GCC_VERSION=8.1.0 make.cross ARCH=riscv
>
> If you fix the issue, kindly add following tag
> Reported-by: kbuild test robot <lkp@intel.com>
>
> All errors (new ones prefixed by >>):
>
>    In file included from fs///attr.c:15:
>    include/linux/fsnotify.h: In function 'fsnotify_nameremove':
> >> include/linux/fsnotify.h:179:23: error: 'struct inode' has no member named 'i_fsnotify_mask'
>      if (!(d_inode(parent)->i_fsnotify_mask & FS_DELETE) &&
>                           ^~
> >> include/linux/fsnotify.h:180:20: error: 'struct super_block' has no member named 's_fsnotify_mask'
>          !(dentry->d_sb->s_fsnotify_mask & FS_DELETE))
>                        ^~
>

Crap! forgot these wrappers are not NOOPed without CONFIG_FSNOTIFY.
It is so annoying to fix bugs in code that should not exist.

In d_delete() at this point, dentry is either negative or inode->i_nlink
which accounts for this name should be decremented.
If d_move() was possible on this dentry, bad things would happen.

I really wish I could just drop this take_dentry_name_snapshot()
and leave the WARN_ON() I suggested instead...
For now will just send an unbroken patch.

Thanks,
Amir.