Re: [PATCH 1/2] filemap: fix the conditional folio_put in filemap_fault

[Jan Kara <jack@suse.cz>]

On Wed 03-05-23 17:45:25, Christoph Hellwig wrote:
> folio can't be NULL here now that __filemap_get_folio returns an
> ERR_PTR.  Remove the conditional folio_put after the out_retry
> label and add a new label for the cases where we have a valid folio.
> 
> Fixes: 66dabbb65d67 ("mm: return an ERR_PTR from __filemap_get_folio")
> Reported-by: syzbot+48011b86c8ea329af1b9@syzkaller.appspotmail.com
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Looks good to me. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

								Honza

> ---
>  mm/filemap.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/filemap.c b/mm/filemap.c
> index a34abfe8c65430..ae597f63a9bc54 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -3298,7 +3298,7 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
>  	}
>  
>  	if (!lock_folio_maybe_drop_mmap(vmf, folio, &fpin))
> -		goto out_retry;
> +		goto out_retry_put_folio;
>  
>  	/* Did it get truncated? */
>  	if (unlikely(folio->mapping != mapping)) {
> @@ -3334,7 +3334,7 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
>  	 */
>  	if (fpin) {
>  		folio_unlock(folio);
> -		goto out_retry;
> +		goto out_retry_put_folio;
>  	}
>  	if (mapping_locked)
>  		filemap_invalidate_unlock_shared(mapping);
> @@ -3363,7 +3363,7 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
>  	fpin = maybe_unlock_mmap_for_io(vmf, fpin);
>  	error = filemap_read_folio(file, mapping->a_ops->read_folio, folio);
>  	if (fpin)
> -		goto out_retry;
> +		goto out_retry_put_folio;
>  	folio_put(folio);
>  
>  	if (!error || error == AOP_TRUNCATED_PAGE)
> @@ -3372,14 +3372,14 @@ vm_fault_t filemap_fault(struct vm_fault *vmf)
>  
>  	return VM_FAULT_SIGBUS;
>  
> +out_retry_put_folio:
> +	folio_put(folio);
>  out_retry:
>  	/*
>  	 * We dropped the mmap_lock, we need to return to the fault handler to
>  	 * re-find the vma and come back and find our hopefully still populated
>  	 * page.
>  	 */
> -	if (folio)
> -		folio_put(folio);
>  	if (mapping_locked)
>  		filemap_invalidate_unlock_shared(mapping);
>  	if (fpin)
> -- 
> 2.39.2
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR