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SubjectRe: [PATCH 3/7] mm: drop the mmap_sem in all read fault cases
On Thu, Oct 18, 2018 at 04:23:14PM -0400, Josef Bacik wrote:
> Johannes' patches didn't quite cover all of the IO cases that we need to
> drop the mmap_sem for, this patch covers the rest of them.
>
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> ---
> mm/filemap.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 1ed35cd99b2c..65395ee132a0 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -2523,6 +2523,7 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
> int error;
> struct mm_struct *mm = vmf->vma->vm_mm;
> struct file *file = vmf->vma->vm_file;
> + struct file *fpin = NULL;
> struct address_space *mapping = file->f_mapping;
> struct file_ra_state *ra = &file->f_ra;
> struct inode *inode = mapping->host;
> @@ -2610,11 +2611,15 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
> return ret | VM_FAULT_LOCKED;
>
> no_cached_page:
> + fpin = maybe_unlock_mmap_for_io(vmf->vma, vmf->flags);
> +
> /*
> * We're only likely to ever get here if MADV_RANDOM is in
> * effect.
> */
> error = page_cache_read(file, offset, vmf->gfp_mask);
> + if (fpin)
> + goto out_retry;

Please put the unlock after the comment explaining the goto label
so it's clear that the pin is associated only with the read
operations like so:

no_cached_page:
/*
* We're only likely to ever get here if MADV_RANDOM is in
* effect.
*/
fpin = maybe_unlock_mmap_for_io(vmf->vma, vmf->flags);
error = page_cache_read(file, offset, vmf->gfp_mask);
if (fpin)
goto out_retry;
>
> /*
> * The page we want has now been added to the page cache.
> @@ -2634,6 +2639,8 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
> return VM_FAULT_SIGBUS;
>
> page_not_uptodate:
> + fpin = maybe_unlock_mmap_for_io(vmf->vma, vmf->flags);
> +
> /*
> * Umm, take care of errors if the page isn't up-to-date.
> * Try to re-read it _once_. We do this synchronously,

Same here.

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com

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