linux-kernel - Re: [PATCH] netfs: Set NETFS_RREQ_WRITE_TO

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Message-ID: <ba17aecba9615f85b7901ea96609abdad3c29db1.camel@hammerspace.com>
Date: Sun, 4 Aug 2024 23:22:04 +0000
From: Trond Myklebust <trondmy@...merspace.com>
To: "max.kellermann@...os.com" <max.kellermann@...os.com>, "hristo@...ev.name"
	<hristo@...ev.name>, "dhowells@...hat.com" <dhowells@...hat.com>
CC: "dan.aloni@...tdata.com" <dan.aloni@...tdata.com>, "xiubli@...hat.com"
	<xiubli@...hat.com>, "linux-fsdevel@...r.kernel.org"
	<linux-fsdevel@...r.kernel.org>, "ceph-devel@...r.kernel.org"
	<ceph-devel@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "netfs@...ts.linux.dev"
	<netfs@...ts.linux.dev>, "jlayton@...nel.org" <jlayton@...nel.org>,
	"idryomov@...il.com" <idryomov@...il.com>, "willy@...radead.org"
	<willy@...radead.org>, "blokos@...e.fr" <blokos@...e.fr>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>
Subject: Re: [PATCH] netfs: Set NETFS_RREQ_WRITE_TO_CACHE when caching is
 possible

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@...r.kernel.org <linux-nfs@...r.kernel.org>
> Cc: blokos <blokos@...e.fr>
> Cc: Trond Myklebust <trondmy@...merspace.com>
> Cc: dan.aloni@...tdata.com <dan.aloni@...tdata.com>
> Signed-off-by: Hristo Venev <hristo@...ev.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@...merspace.com