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@xxxxxxxxx>
> CC: stable@xxxxxxxxxxxxxxx # Needed by "xfs: Fix stale data exposure
> when readahead races with hole punch"
> Signed-off-by: Jan Kara <jack@xxxxxxx>
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@xxxxxxxxxx>
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(¤t->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(¤t->mm->mmap_sem);
> return 0;
> }
>
>
