Re: [linux-next:master] BUILD REGRESSION 605cbf3d5f20470ec303b79feda3202935f4a142

[Amir Goldstein <amir73il@gmail.com>]

On Thu, Aug 20, 2020 at 11:40 PM Andrew Morton
<akpm@linux-foundation.org> wrote:
>
> On Fri, 21 Aug 2020 04:26:12 +0800 kernel test robot <lkp@intel.com> wrote:
>
> > tree/branch: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git  master
> > branch HEAD: 605cbf3d5f20470ec303b79feda3202935f4a142  Add linux-next specific files for 20200820
> >
> > Error/Warning in current branch:
> >
> > fs/notify/fsnotify.c:460 fsnotify() warn: variable dereferenced before check 'inode' (see line 449)
>
> Yes, this:
>
> :       if (!inode) {
> :               /* Dirent event - report on TYPE_INODE to dir */
> :               inode = dir;
> :       } else if (mask & FS_EVENT_ON_CHILD) {
> :               /*
> :                * Event on child - report on TYPE_INODE to dir if it is
> :                * watching children and on TYPE_CHILD to child.
> :                */
> :               child = inode;
> :               inode = dir;
> :       }
>
> `inode' is non-NULL here.
>
> :       sb = inode->i_sb;
>
> So this is OK.
>
> :       /*
> :        * Optimization: srcu_read_lock() has a memory barrier which can
> :        * be expensive.  It protects walking the *_fsnotify_marks lists.
> :        * However, if we do not walk the lists, we do not have to do
> :        * SRCU because we have no references to any objects and do not
> :        * need SRCU to keep them "alive".
> :        */
> :       if (!sb->s_fsnotify_marks &&
> :           (!mnt || !mnt->mnt_fsnotify_marks) &&
> :           (!inode || !inode->i_fsnotify_marks) &&
>
> So !inode is always false.
>
> :           (!child || !child->i_fsnotify_marks))
> :               return 0;
>
> I assume we can just zap the "!inode ||".  Amir & Jan, can you
> please take a look?
>

Andrew,

This warning was brought to our attention.
We both agreed that we like the code as it is with the unneeded !inode check.

https://lore.kernel.org/linux-fsdevel/20200730192537.GB13525@quack2.suse.cz/

Thanks,
Amir.