Re: [PATCH] netfs: Set NETFS_RREQ_WRITE_TO_CACHE when caching is possible

[Trond Myklebust <trondmy@hammerspace.com>]

On Sun, 2024-08-04 at 16:57 +0300, Hristo Venev wrote:
> In addition to Ceph, in NFS there are also some crashes related to
> the
> use of 0x356 as a pointer.
> 
> `netfs_is_cache_enabled()` only returns true when the fscache cookie
> is
> fully initialized. This may happen after the request has been
> created,
> so check for the cookie's existence instead.
> 
> Link:
> https://lore.kernel.org/linux-nfs/b78c88db-8b3a-4008-94cb-82ae08f0e37b@free.fr/T/
> Fixes: 2ff1e97587f4 ("netfs: Replace PG_fscache by setting folio-
> >private and marking dirty")
> Cc: linux-nfs@vger.kernel.org <linux-nfs@vger.kernel.org>
> Cc: blokos <blokos@free.fr>
> Cc: Trond Myklebust <trondmy@hammerspace.com>
> Cc: dan.aloni@vastdata.com <dan.aloni@vastdata.com>
> Signed-off-by: Hristo Venev <hristo@venev.name>
> ---
>  fs/netfs/objects.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/netfs/objects.c b/fs/netfs/objects.c
> index f4a6427274792..a74ca90c86c9b 100644
> --- a/fs/netfs/objects.c
> +++ b/fs/netfs/objects.c
> @@ -27,7 +27,6 @@ struct netfs_io_request *netfs_alloc_request(struct
> address_space *mapping,
>  	bool is_unbuffered = (origin == NETFS_UNBUFFERED_WRITE ||
>  			      origin == NETFS_DIO_READ ||
>  			      origin == NETFS_DIO_WRITE);
> -	bool cached = !is_unbuffered && netfs_is_cache_enabled(ctx);
>  	int ret;
>  
>  	for (;;) {
> @@ -56,8 +55,9 @@ struct netfs_io_request *netfs_alloc_request(struct
> address_space *mapping,
>  	refcount_set(&rreq->ref, 1);
>  
>  	__set_bit(NETFS_RREQ_IN_PROGRESS, &rreq->flags);
> -	if (cached) {
> -		__set_bit(NETFS_RREQ_WRITE_TO_CACHE, &rreq->flags);
> +	if (!is_unbuffered &&
> fscache_cookie_valid(netfs_i_cookie(ctx))) {
> +		if(netfs_is_cache_enabled(ctx))
> +			__set_bit(NETFS_RREQ_WRITE_TO_CACHE, &rreq-
> >flags);
>  		if (test_bit(NETFS_ICTX_USE_PGPRIV2, &ctx->flags))
>  			/* Filesystem uses deprecated PG_private_2
> marking. */
>  			__set_bit(NETFS_RREQ_USE_PGPRIV2, &rreq-
> >flags);

Does this mean that netfs could still end up setting a value for folio-
>private in NFS given some other set of circumstances?


-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com