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114143a595
linux/fs/nfs/fscache.h
David Howells 7b589a9b45
netfs: Fix handling of USE_PGPRIV2 and WRITE_TO_CACHE flags 
The NETFS_RREQ_USE_PGPRIV2 and NETFS_RREQ_WRITE_TO_CACHE flags aren't used
correctly.  The problem is that we try to set them up in the request
initialisation, but we the cache may be in the process of setting up still,
and so the state may not be correct.  Further, we secondarily sample the
cache state and make contradictory decisions later.

The issue arises because we set up the cache resources, which allows the
cache's ->prepare_read() to switch on NETFS_SREQ_COPY_TO_CACHE - which
triggers cache writing even if we didn't set the flags when allocating.

Fix this in the following way:

 (1) Drop NETFS_ICTX_USE_PGPRIV2 and instead set NETFS_RREQ_USE_PGPRIV2 in
     ->init_request() rather than trying to juggle that in
     netfs_alloc_request().

 (2) Repurpose NETFS_RREQ_USE_PGPRIV2 to merely indicate that if caching is
     to be done, then PG_private_2 is to be used rather than only setting
     it if we decide to cache and then having netfs_rreq_unlock_folios()
     set the non-PG_private_2 writeback-to-cache if it wasn't set.

 (3) Split netfs_rreq_unlock_folios() into two functions, one of which
     contains the deprecated code for using PG_private_2 to avoid
     accidentally doing the writeback path - and always use it if
     USE_PGPRIV2 is set.

 (4) As NETFS_ICTX_USE_PGPRIV2 is removed, make netfs_write_begin() always
     wait for PG_private_2.  This function is deprecated and only used by
     ceph anyway, and so label it so.

 (5) Drop the NETFS_RREQ_WRITE_TO_CACHE flag and use
     fscache_operation_valid() on the cache_resources instead.  This has
     the advantage of picking up the result of netfs_begin_cache_read() and
     fscache_begin_write_operation() - which are called after the object is
     initialised and will wait for the cache to come to a usable state.

Just reverting ae678317b95e[1] isn't a sufficient fix, so this need to be
applied on top of that.  Without this as well, things like:

 rcu: INFO: rcu_sched detected expedited stalls on CPUs/tasks: {

and:

 WARNING: CPU: 13 PID: 3621 at fs/ceph/caps.c:3386

may happen, along with some UAFs due to PG_private_2 not getting used to
wait on writeback completion.

Fixes: 2ff1e97587 ("netfs: Replace PG_fscache by setting folio->private and marking dirty")
Reported-by: Max Kellermann <max.kellermann@ionos.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Ilya Dryomov <idryomov@gmail.com>
cc: Xiubo Li <xiubli@redhat.com>
cc: Hristo Venev <hristo@venev.name>
cc: Jeff Layton <jlayton@kernel.org>
cc: Matthew Wilcox <willy@infradead.org>
cc: ceph-devel@vger.kernel.org
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
cc: linux-mm@kvack.org
Link: https://lore.kernel.org/r/3575457.1722355300@warthog.procyon.org.uk/ [1]
Link: https://lore.kernel.org/r/1173209.1723152682@warthog.procyon.org.uk
Signed-off-by: Christian Brauner <brauner@kernel.org>
2024-08-12 22:03:27 +02:00

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/* SPDX-License-Identifier: GPL-2.0-or-later */
/* NFS filesystem cache interface definitions
*
* Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*/
#ifndef _NFS_FSCACHE_H
#define _NFS_FSCACHE_H
#include <linux/swap.h>
#include <linux/nfs_fs.h>
#include <linux/nfs_mount.h>
#include <linux/nfs4_mount.h>
#include <linux/fscache.h>
#include <linux/iversion.h>
#ifdef CONFIG_NFS_FSCACHE
/*
* Definition of the auxiliary data attached to NFS inode storage objects
* within the cache.
*
* The contents of this struct are recorded in the on-disk local cache in the
* auxiliary data attached to the data storage object backing an inode. This
* permits coherency to be managed when a new inode binds to an already extant
* cache object.
*/
struct nfs_fscache_inode_auxdata {
s64 mtime_sec;
s64 mtime_nsec;
s64 ctime_sec;
s64 ctime_nsec;
u64 change_attr;
};
struct nfs_netfs_io_data {
/*
* NFS may split a netfs_io_subrequest into multiple RPCs, each
* with their own read completion. In netfs, we can only call
* netfs_subreq_terminated() once for each subrequest. Use the
* refcount here to double as a marker of the last RPC completion,
* and only call netfs via netfs_subreq_terminated() once.
*/
refcount_t refcount;
struct netfs_io_subrequest *sreq;
/*
* Final disposition of the netfs_io_subrequest, sent in
* netfs_subreq_terminated()
*/
atomic64_t transferred;
int error;
};
static inline void nfs_netfs_get(struct nfs_netfs_io_data *netfs)
{
refcount_inc(&netfs->refcount);
}
static inline void nfs_netfs_put(struct nfs_netfs_io_data *netfs)
{
ssize_t final_len;
/* Only the last RPC completion should call netfs_subreq_terminated() */
if (!refcount_dec_and_test(&netfs->refcount))
return;
/*
* The NFS pageio interface may read a complete page, even when netfs
* only asked for a partial page. Specifically, this may be seen when
* one thread is truncating a file while another one is reading the last
* page of the file.
* Correct the final length here to be no larger than the netfs subrequest
* length, and thus avoid netfs's "Subreq overread" warning message.
*/
final_len = min_t(s64, netfs->sreq->len, atomic64_read(&netfs->transferred));
netfs_subreq_terminated(netfs->sreq, netfs->error ?: final_len, false);
kfree(netfs);
}
static inline void nfs_netfs_inode_init(struct nfs_inode *nfsi)
{
netfs_inode_init(&nfsi->netfs, &nfs_netfs_ops, false);
}
extern void nfs_netfs_initiate_read(struct nfs_pgio_header *hdr);
extern void nfs_netfs_read_completion(struct nfs_pgio_header *hdr);
extern int nfs_netfs_folio_unlock(struct folio *folio);
/*
* fscache.c
*/
extern int nfs_fscache_get_super_cookie(struct super_block *, const char *, int);
extern void nfs_fscache_release_super_cookie(struct super_block *);
extern void nfs_fscache_init_inode(struct inode *);
extern void nfs_fscache_clear_inode(struct inode *);
extern void nfs_fscache_open_file(struct inode *, struct file *);
extern void nfs_fscache_release_file(struct inode *, struct file *);
extern int nfs_netfs_readahead(struct readahead_control *ractl);
extern int nfs_netfs_read_folio(struct file *file, struct folio *folio);
static inline bool nfs_fscache_release_folio(struct folio *folio, gfp_t gfp)
{
if (folio_test_private_2(folio)) { /* [DEPRECATED] */
if (current_is_kswapd() || !(gfp & __GFP_FS))
return false;
folio_wait_private_2(folio);
}
fscache_note_page_release(netfs_i_cookie(netfs_inode(folio->mapping->host)));
return true;
}
static inline void nfs_fscache_update_auxdata(struct nfs_fscache_inode_auxdata *auxdata,
struct inode *inode)
{
memset(auxdata, 0, sizeof(*auxdata));
auxdata->mtime_sec = inode_get_mtime(inode).tv_sec;
auxdata->mtime_nsec = inode_get_mtime(inode).tv_nsec;
auxdata->ctime_sec = inode_get_ctime(inode).tv_sec;
auxdata->ctime_nsec = inode_get_ctime(inode).tv_nsec;
if (NFS_SERVER(inode)->nfs_client->rpc_ops->version == 4)
auxdata->change_attr = inode_peek_iversion_raw(inode);
}
/*
* Invalidate the contents of fscache for this inode. This will not sleep.
*/
static inline void nfs_fscache_invalidate(struct inode *inode, int flags)
{
struct nfs_fscache_inode_auxdata auxdata;
struct fscache_cookie *cookie = netfs_i_cookie(&NFS_I(inode)->netfs);
nfs_fscache_update_auxdata(&auxdata, inode);
fscache_invalidate(cookie, &auxdata, i_size_read(inode), flags);
}
/*
* indicate the client caching state as readable text
*/
static inline const char *nfs_server_fscache_state(struct nfs_server *server)
{
if (server->fscache)
return "yes";
return "no ";
}
static inline void nfs_netfs_set_pgio_header(struct nfs_pgio_header *hdr,
struct nfs_pageio_descriptor *desc)
{
hdr->netfs = desc->pg_netfs;
}
static inline void nfs_netfs_set_pageio_descriptor(struct nfs_pageio_descriptor *desc,
struct nfs_pgio_header *hdr)
{
desc->pg_netfs = hdr->netfs;
}
static inline void nfs_netfs_reset_pageio_descriptor(struct nfs_pageio_descriptor *desc)
{
desc->pg_netfs = NULL;
}
#else /* CONFIG_NFS_FSCACHE */
static inline void nfs_netfs_inode_init(struct nfs_inode *nfsi) {}
static inline void nfs_netfs_initiate_read(struct nfs_pgio_header *hdr) {}
static inline void nfs_netfs_read_completion(struct nfs_pgio_header *hdr) {}
static inline int nfs_netfs_folio_unlock(struct folio *folio)
{
return 1;
}
static inline void nfs_fscache_release_super_cookie(struct super_block *sb) {}
static inline void nfs_fscache_init_inode(struct inode *inode) {}
static inline void nfs_fscache_clear_inode(struct inode *inode) {}
static inline void nfs_fscache_open_file(struct inode *inode,
struct file *filp) {}
static inline void nfs_fscache_release_file(struct inode *inode, struct file *file) {}
static inline int nfs_netfs_readahead(struct readahead_control *ractl)
{
return -ENOBUFS;
}
static inline int nfs_netfs_read_folio(struct file *file, struct folio *folio)
{
return -ENOBUFS;
}
static inline bool nfs_fscache_release_folio(struct folio *folio, gfp_t gfp)
{
return true; /* may release folio */
}
static inline void nfs_fscache_invalidate(struct inode *inode, int flags) {}
static inline const char *nfs_server_fscache_state(struct nfs_server *server)
{
return "no ";
}
static inline void nfs_netfs_set_pgio_header(struct nfs_pgio_header *hdr,
struct nfs_pageio_descriptor *desc) {}
static inline void nfs_netfs_set_pageio_descriptor(struct nfs_pageio_descriptor *desc,
struct nfs_pgio_header *hdr) {}
static inline void nfs_netfs_reset_pageio_descriptor(struct nfs_pageio_descriptor *desc) {}
#endif /* CONFIG_NFS_FSCACHE */
#endif /* _NFS_FSCACHE_H */
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