[PATCH 5/9] mm: drop the mmap_sem in all read fault cases

[Josef Bacik]

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 <jo...@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;
 
        /*
         * 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,
@@ -2647,6 +2654,8 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
                if (!PageUptodate(page))
                        error = -EIO;
        }
+       if (fpin)
+               goto out_retry;
        put_page(page);
 
        if (!error || error == AOP_TRUNCATED_PAGE)
@@ -2665,6 +2674,8 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
        }
 
 out_retry:
+       if (fpin)
+               fput(fpin);
        if (page)
                put_page(page);
        return ret | VM_FAULT_RETRY;
-- 
2.14.3