Re: [PATCH 1/3] mm: Handle MADV_WILLNEED through vfs_fadvise()

On 11/07/2019 17:00, Jan Kara wrote:

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 amir73il@gmail.com CC: stable@vger.kernel.org # Needed by "xfs: Fix stale data exposure when readahead races with hole punch" Signed-off-by: Jan Kara jack@suse.cz

I had a similar patch for my needs. But did not drop the mmap_sem when calling into the FS. This one is much better.

Reviewed-by: Boaz Harrosh boazh@netapp.com

I tested this patch, Works perfect for my needs.

Thank you for this patch Boaz

---

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

diff --git a/mm/madvise.c b/mm/madvise.c index 628022e674a7..ae56d0ef337d 100644 --- 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_area_struct *vma, 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_area_struct *vma, 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;

}