[PATCH] block: Fix dio_bio_alloc() to set BIO_PAGE_PINNED

[PATCH] block: Fix dio_bio_alloc() to set BIO_PAGE_PINNED

[David Howells]

    
Fix dio_bio_alloc() to set BIO_PAGE_PINNED, not BIO_PAGE_REFFED, so that
the bio code unpins the pinned pages rather than putting a ref on them.

The issue was causing:

        WARNING: CPU: 6 PID: 2220 at mm/gup.c:76 try_get_folio

This can be caused by creating a file on a loopback UDF filesystem, opening
it O_DIRECT and making two writes to it from the same source buffer.

Fixes: 1ccf164ec866 ("block: Use iov_iter_extract_pages() and page pinning in direct-io.c")
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202306120931.a9606b88-oliver.sang@intel.com
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Christoph Hellwig <hch@infradead.org>
cc: David Hildenbrand <david@redhat.com>
cc: Andrew Morton <akpm@linux-foundation.org>
cc: Jens Axboe <axboe@kernel.dk>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: Matthew Wilcox <willy@infradead.org>
cc: Jan Kara <jack@suse.cz>
cc: Jeff Layton <jlayton@kernel.org>
cc: Jason Gunthorpe <jgg@nvidia.com>
cc: Logan Gunthorpe <logang@deltatee.com>
cc: Hillf Danton <hdanton@sina.com>
cc: Christian Brauner <brauner@kernel.org>
cc: Linus Torvalds <torvalds@linux-foundation.org>
cc: linux-fsdevel@vger.kernel.org
cc: linux-block@vger.kernel.org
cc: linux-kernel@vger.kernel.org
cc: linux-mm@kvack.org
---
 fs/direct-io.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/direct-io.c b/fs/direct-io.c
index 14049204cac8..04e810826ee8 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -415,7 +415,8 @@ dio_bio_alloc(struct dio *dio, struct dio_submit *sdio,
 	else
 		bio->bi_end_io = dio_bio_end_io;
 	/* for now require references for all pages */
-	bio_set_flag(bio, BIO_PAGE_REFFED);
+	if (dio->need_unpin)
+		bio_set_flag(bio, BIO_PAGE_PINNED);
 	sdio->bio = bio;
 	sdio->logical_offset_in_bio = sdio->cur_page_fs_offset;
 }

Re: [PATCH] block: Fix dio_bio_alloc() to set BIO_PAGE_PINNED

[David Hildenbrand]

On 12.06.23 18:51, David Howells wrote:
>      
> Fix dio_bio_alloc() to set BIO_PAGE_PINNED, not BIO_PAGE_REFFED, so that
> the bio code unpins the pinned pages rather than putting a ref on them.
> 
> The issue was causing:
> 
>          WARNING: CPU: 6 PID: 2220 at mm/gup.c:76 try_get_folio
> 
> This can be caused by creating a file on a loopback UDF filesystem, opening
> it O_DIRECT and making two writes to it from the same source buffer.
> 
> Fixes: 1ccf164ec866 ("block: Use iov_iter_extract_pages() and page pinning in direct-io.c")
> Reported-by: kernel test robot <oliver.sang@intel.com>
> Closes: https://lore.kernel.org/oe-lkp/202306120931.a9606b88-oliver.sang@intel.com
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: Christoph Hellwig <hch@infradead.org>
> cc: David Hildenbrand <david@redhat.com>
> cc: Andrew Morton <akpm@linux-foundation.org>
> cc: Jens Axboe <axboe@kernel.dk>
> cc: Al Viro <viro@zeniv.linux.org.uk>
> cc: Matthew Wilcox <willy@infradead.org>
> cc: Jan Kara <jack@suse.cz>
> cc: Jeff Layton <jlayton@kernel.org>
> cc: Jason Gunthorpe <jgg@nvidia.com>
> cc: Logan Gunthorpe <logang@deltatee.com>
> cc: Hillf Danton <hdanton@sina.com>
> cc: Christian Brauner <brauner@kernel.org>
> cc: Linus Torvalds <torvalds@linux-foundation.org>
> cc: linux-fsdevel@vger.kernel.org
> cc: linux-block@vger.kernel.org
> cc: linux-kernel@vger.kernel.org
> cc: linux-mm@kvack.org
> ---
>   fs/direct-io.c |    3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> index 14049204cac8..04e810826ee8 100644
> --- a/fs/direct-io.c
> +++ b/fs/direct-io.c
> @@ -415,7 +415,8 @@ dio_bio_alloc(struct dio *dio, struct dio_submit *sdio,
>   	else
>   		bio->bi_end_io = dio_bio_end_io;
>   	/* for now require references for all pages */

Does the comment still hold?

> -	bio_set_flag(bio, BIO_PAGE_REFFED);
> +	if (dio->need_unpin)
> +		bio_set_flag(bio, BIO_PAGE_PINNED);
>   	sdio->bio = bio;
>   	sdio->logical_offset_in_bio = sdio->cur_page_fs_offset;
>   }
> 

-- 
Cheers,

David / dhildenb

Re: [PATCH] block: Fix dio_bio_alloc() to set BIO_PAGE_PINNED

[David Howells]

David Hildenbrand <david@redhat.com> wrote:

> >   	/* for now require references for all pages */
> 
> Does the comment still hold?

Actually, no.

David

Re: [PATCH] block: Fix dio_bio_alloc() to set BIO_PAGE_PINNED

[David Howells]

Okay, it isn't this.  The problem appears to be that __blockdev_direct_IO()
calls dio_cleanup() twice if do_direct_IO() fails.

David

Re: [PATCH] block: Fix dio_bio_alloc() to set BIO_PAGE_PINNED

[David Howells]

 static inline void dio_cleanup(struct dio *dio, struct dio_submit *sdio)
 {
-       while (sdio->head < sdio->tail)
-               put_page(dio->pages[sdio->head++]);
+       if (dio->is_pinned)
+               unpin_user_pages(dio->pages + sdio->head,
+                                sdio->tail - sdio->head);
 }
 
 /*

Meh.  It's obvious.  Need to advance head.

David