mm/readahead: pass a file_ra_state into force_page_cache_ra

The file_ra_state being passed into page_cache_sync_readahead() was being
ignored in favour of using the one embedded in the struct file.  The only
caller for which this makes a difference is the fsverity code if the file
has been marked as POSIX_FADV_RANDOM, but it's confusing and worth fixing.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Eric Biggers <ebiggers@google.com>
Link: https://lkml.kernel.org/r/20200903140844.14194-10-willy@infradead.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/internal.h

@@ -51,12 +51,13 @@ void unmap_page_range(struct mmu_gather *tlb,
 
 void do_page_cache_ra(struct readahead_control *, unsigned long nr_to_read,
 		unsigned long lookahead_size);
-void force_page_cache_ra(struct readahead_control *, unsigned long nr);
+void force_page_cache_ra(struct readahead_control *, struct file_ra_state *,
+		unsigned long nr);
 static inline void force_page_cache_readahead(struct address_space *mapping,
 		struct file *file, pgoff_t index, unsigned long nr_to_read)
 {
 	DEFINE_READAHEAD(ractl, file, mapping, index);
-	force_page_cache_ra(&ractl, nr_to_read);
+	force_page_cache_ra(&ractl, &file->f_ra, nr_to_read);
 }
 
 struct page *find_get_entry(struct address_space *mapping, pgoff_t index);

mm/readahead.c

@@ -272,11 +272,10 @@ void do_page_cache_ra(struct readahead_control *ractl,
  * memory at once.
  */
 void force_page_cache_ra(struct readahead_control *ractl,
-		unsigned long nr_to_read)
+		struct file_ra_state *ra, unsigned long nr_to_read)
 {
 	struct address_space *mapping = ractl->mapping;
 	struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
-	struct file_ra_state *ra = &ractl->file->f_ra;
 	unsigned long max_pages, index;
 
 	if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages &&
@@ -562,7 +561,7 @@ void page_cache_sync_ra(struct readahead_control *ractl,
 
 	/* be dumb */
 	if (ractl->file && (ractl->file->f_mode & FMODE_RANDOM)) {
-		force_page_cache_ra(ractl, req_count);
+		force_page_cache_ra(ractl, ra, req_count);
 		return;
 	}