Re: [bug report] mm: Provide a means of invalidation without using launder_folio

[Matthew Wilcox <willy@infradead.org>]

On Thu, Jun 13, 2024 at 04:55:30PM +0300, Dan Carpenter wrote:
> Hello David Howells,
> 
> Commit 74e797d79cf1 ("mm: Provide a means of invalidation without
> using launder_folio") from Mar 27, 2024 (linux-next), leads to the
> following Smatch static checker warning:
> 
> 	mm/filemap.c:4229 filemap_invalidate_inode()
> 	error: we previously assumed 'mapping' could be null (see line 4200)

I think David has been overly cautious here.  I don't think i_mapping
can ever be NULL.  inode_init_always() sets i_mapping to be
&inode->i_data and I don't see anywhere that changes i_mapping to be
NULL.

> mm/filemap.c
>   4192  int filemap_invalidate_inode(struct inode *inode, bool flush,
>   4193                               loff_t start, loff_t end)
>   4194  {
>   4195          struct address_space *mapping = inode->i_mapping;
>   4196          pgoff_t first = start >> PAGE_SHIFT;
>   4197          pgoff_t last = end >> PAGE_SHIFT;
>   4198          pgoff_t nr = end == LLONG_MAX ? ULONG_MAX : last - first + 1;
>   4199  
>   4200          if (!mapping || !mapping->nrpages || end < start)
>                     ^^^^^^^^
> If mapping is NULL