[PATCH 5.2 298/313] mm: Handle MADV_WILLNEED through vfs_fadvise()

[Greg Kroah-Hartman]

From: Jan Kara <j...@suse.cz>

commit 692fe62433d4ca47605b39f7c416efd6679ba694 upstream.

Currently handling of MADV_WILLNEED hint calls directly into readahead
code. Handle it by calling vfs_fadvise() instead so that filesystem can
use its ->fadvise() callback to acquire necessary locks or otherwise
prepare for the request.

Suggested-by: Amir Goldstein <amir7...@gmail.com>
Reviewed-by: Boaz Harrosh <bo...@netapp.com>
CC: sta...@vger.kernel.org
Signed-off-by: Jan Kara <j...@suse.cz>
Reviewed-by: Darrick J. Wong <darrick.w...@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.w...@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 mm/madvise.c |   22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -14,6 +14,7 @@
 #include <linux/userfaultfd_k.h>
 #include <linux/hugetlb.h>
 #include <linux/falloc.h>
+#include <linux/fadvise.h>
 #include <linux/sched.h>
 #include <linux/ksm.h>
 #include <linux/fs.h>
@@ -275,6 +276,7 @@ static long madvise_willneed(struct vm_a
                             unsigned long start, unsigned long end)
 {
        struct file *file = vma->vm_file;
+       loff_t offset;
 
        *prev = vma;
 #ifdef CONFIG_SWAP
@@ -298,12 +300,20 @@ static long madvise_willneed(struct vm_a
                return 0;
        }
 
-       start = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
-       if (end > vma->vm_end)
-               end = vma->vm_end;
-       end = ((end - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
-
-       force_page_cache_readahead(file->f_mapping, file, start, end - start);
+       /*
+        * Filesystem's fadvise may need to take various locks.  We need to
+        * explicitly grab a reference because the vma (and hence the
+        * vma's reference to the file) can go away as soon as we drop
+        * mmap_sem.
+        */
+       *prev = NULL;   /* tell sys_madvise we drop mmap_sem */
+       get_file(file);
+       up_read(&current->mm->mmap_sem);
+       offset = (loff_t)(start - vma->vm_start)
+                       + ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
+       vfs_fadvise(file, offset, end - start, POSIX_FADV_WILLNEED);
+       fput(file);
+       down_read(&current->mm->mmap_sem);
        return 0;
 }