[RFC PATCH 32/37] f2fs: implement speculative fault handling

[Michel Lespinasse]

We just need to make sure f2fs_filemap_fault() doesn't block in the
speculative case as it is called with an rcu read lock held.

Signed-off-by: Michel Lespinasse <mic...@lespinasse.org>
---
 fs/f2fs/file.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index d26ff2ae3f5e..c1cfdc3ec98e 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -37,7 +37,12 @@ static vm_fault_t f2fs_filemap_fault(struct vm_fault *vmf)
        struct inode *inode = file_inode(vmf->vma->vm_file);
        vm_fault_t ret;
 
-       down_read(&F2FS_I(inode)->i_mmap_sem);
+       if (vmf->flags & FAULT_FLAG_SPECULATIVE) {
+               if (!down_read_trylock(&F2FS_I(inode)->i_mmap_sem))
+                       return VM_FAULT_RETRY;
+       } else {
+               down_read(&F2FS_I(inode)->i_mmap_sem);
+       }
        ret = filemap_fault(vmf);
        up_read(&F2FS_I(inode)->i_mmap_sem);
 
@@ -171,6 +176,7 @@ static const struct vm_operations_struct f2fs_file_vm_ops = 
{
        .fault          = f2fs_filemap_fault,
        .map_pages      = filemap_map_pages,
        .page_mkwrite   = f2fs_vm_page_mkwrite,
+       .speculative    = true,
 };
 
 static int get_parent_ino(struct inode *inode, nid_t *pino)
-- 
2.20.1