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linux/fs/nfs/fscache.h
David Howells f1fe29b4a0 NFS: Use i_writecount to control whether to get an fscache cookie in nfs_open()
Use i_writecount to control whether to get an fscache cookie in nfs_open() as
NFS does not do write caching yet.  I *think* this is the cause of a problem
encountered by Mark Moseley whereby __fscache_uncache_page() gets a NULL
pointer dereference because cookie->def is NULL:

BUG: unable to handle kernel NULL pointer dereference at 0000000000000010
IP: [<ffffffff812a1903>] __fscache_uncache_page+0x23/0x160
PGD 0
Thread overran stack, or stack corrupted
Oops: 0000 [] SMP
Modules linked in: ...
CPU: 7 PID: 18993 Comm: php Not tainted 3.11.1 
Hardware name: Dell Inc. PowerEdge R420/072XWF, BIOS 1.3.5 08/21/2012
task: ffff8804203460c0 ti: ffff880420346640
RIP: 0010:[<ffffffff812a1903>] __fscache_uncache_page+0x23/0x160
RSP: 0018:ffff8801053af878 EFLAGS: 00210286
RAX: 0000000000000000 RBX: ffff8800be2f8780 RCX: ffff88022ffae5e8
RDX: 0000000000004c66 RSI: ffffea00055ff440 RDI: ffff8800be2f8780
RBP: ffff8801053af898 R08: 0000000000000001 R09: 0000000000000003
R10: 0000000000000000 R11: 0000000000000000 R12: ffffea00055ff440
R13: 0000000000001000 R14: ffff8800c50be538 R15: 0000000000000000
FS: 0000000000000000(0000) GS:ffff88042fc60000(0063) knlGS:00000000e439c700
CS: 0010 DS: 002b ES: 002b CR0: 0000000080050033
CR2: 0000000000000010 CR3: 0000000001d8f000 CR4: 00000000000607f0
Stack:
...
Call Trace:
[<ffffffff81365a72>] __nfs_fscache_invalidate_page+0x42/0x70
[<ffffffff813553d5>] nfs_invalidate_page+0x75/0x90
[<ffffffff811b8f5e>] truncate_inode_page+0x8e/0x90
[<ffffffff811b90ad>] truncate_inode_pages_range.part.12+0x14d/0x620
[<ffffffff81d6387d>] ? __mutex_lock_slowpath+0x1fd/0x2e0
[<ffffffff811b95d3>] truncate_inode_pages_range+0x53/0x70
[<ffffffff811b969d>] truncate_inode_pages+0x2d/0x40
[<ffffffff811b96ff>] truncate_pagecache+0x4f/0x70
[<ffffffff81356840>] nfs_setattr_update_inode+0xa0/0x120
[<ffffffff81368de4>] nfs3_proc_setattr+0xc4/0xe0
[<ffffffff81357f78>] nfs_setattr+0xc8/0x150
[<ffffffff8122d95b>] notify_change+0x1cb/0x390
[<ffffffff8120a55b>] do_truncate+0x7b/0xc0
[<ffffffff8121f96c>] do_last+0xa4c/0xfd0
[<ffffffff8121ffbc>] path_openat+0xcc/0x670
[<ffffffff81220a0e>] do_filp_open+0x4e/0xb0
[<ffffffff8120ba1f>] do_sys_open+0x13f/0x2b0
[<ffffffff8126aaf6>] compat_SyS_open+0x36/0x50
[<ffffffff81d7204c>] sysenter_dispatch+0x7/0x24

The code at the instruction pointer was disassembled:

> (gdb) disas __fscache_uncache_page
> Dump of assembler code for function __fscache_uncache_page:
> ...
> 0xffffffff812a18ff <+31>: mov 0x48(%rbx),%rax
> 0xffffffff812a1903 <+35>: cmpb $0x0,0x10(%rax)
> 0xffffffff812a1907 <+39>: je 0xffffffff812a19cd <__fscache_uncache_page+237>

These instructions make up:

	ASSERTCMP(cookie->def->type, !=, FSCACHE_COOKIE_TYPE_INDEX);

That cmpb is the faulting instruction (%rax is 0).  So cookie->def is NULL -
which presumably means that the cookie has already been at least partway
through __fscache_relinquish_cookie().

What I think may be happening is something like a three-way race on the same
file:

	PROCESS 1	PROCESS 2	PROCESS 3
	===============	===============	===============
	open(O_TRUNC|O_WRONLY)
			open(O_RDONLY)
					open(O_WRONLY)
	-->nfs_open()
	-->nfs_fscache_set_inode_cookie()
	nfs_fscache_inode_lock()
	nfs_fscache_disable_inode_cookie()
	__fscache_relinquish_cookie()
	nfs_inode->fscache = NULL
	<--nfs_fscache_set_inode_cookie()

			-->nfs_open()
			-->nfs_fscache_set_inode_cookie()
			nfs_fscache_inode_lock()
			nfs_fscache_enable_inode_cookie()
			__fscache_acquire_cookie()
			nfs_inode->fscache = cookie
			<--nfs_fscache_set_inode_cookie()
	<--nfs_open()
	-->nfs_setattr()
	...
	...
	-->nfs_invalidate_page()
	-->__nfs_fscache_invalidate_page()
	cookie = nfsi->fscache
					-->nfs_open()
					-->nfs_fscache_set_inode_cookie()
					nfs_fscache_inode_lock()
					nfs_fscache_disable_inode_cookie()
					-->__fscache_relinquish_cookie()
	-->__fscache_uncache_page(cookie)
	<crash>
					<--__fscache_relinquish_cookie()
					nfs_inode->fscache = NULL
					<--nfs_fscache_set_inode_cookie()

What is needed is something to prevent process  from reacquiring the cookie
- and I think checking i_writecount should do the trick.

It's also possible to have a two-way race on this if the file is opened
O_TRUNC|O_RDONLY instead.

Reported-by: Mark Moseley <moseleymark@gmail.com>
Signed-off-by: David Howells <dhowells@redhat.com>
2013-09-27 18:40:25 +01:00

230 lines
6.5 KiB
C

/* NFS filesystem cache interface definitions
*
* Copyright (C) 2008 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public Licence
* as published by the Free Software Foundation; either version
* 2 of the Licence, or (at your option) any later version.
*/
#ifndef _NFS_FSCACHE_H
#define _NFS_FSCACHE_H
#include <linux/nfs_fs.h>
#include <linux/nfs_mount.h>
#include <linux/nfs4_mount.h>
#include <linux/fscache.h>
#ifdef CONFIG_NFS_FSCACHE
/*
* set of NFS FS-Cache objects that form a superblock key
*/
struct nfs_fscache_key {
struct rb_node node;
struct nfs_client *nfs_client; /* the server */
/* the elements of the unique key - as used by nfs_compare_super() and
* nfs_compare_mount_options() to distinguish superblocks */
struct {
struct {
unsigned long s_flags; /* various flags
* (& NFS_MS_MASK) */
} super;
struct {
struct nfs_fsid fsid;
int flags;
unsigned int rsize; /* read size */
unsigned int wsize; /* write size */
unsigned int acregmin; /* attr cache timeouts */
unsigned int acregmax;
unsigned int acdirmin;
unsigned int acdirmax;
} nfs_server;
struct {
rpc_authflavor_t au_flavor;
} rpc_auth;
/* uniquifier - can be used if nfs_server.flags includes
* NFS_MOUNT_UNSHARED */
u8 uniq_len;
char uniquifier[0];
} key;
};
/*
* fscache-index.c
*/
extern struct fscache_netfs nfs_fscache_netfs;
extern const struct fscache_cookie_def nfs_fscache_server_index_def;
extern const struct fscache_cookie_def nfs_fscache_super_index_def;
extern const struct fscache_cookie_def nfs_fscache_inode_object_def;
extern int nfs_fscache_register(void);
extern void nfs_fscache_unregister(void);
/*
* fscache.c
*/
extern void nfs_fscache_get_client_cookie(struct nfs_client *);
extern void nfs_fscache_release_client_cookie(struct nfs_client *);
extern void 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_invalidate_page(struct page *, struct inode *);
extern int nfs_fscache_release_page(struct page *, gfp_t);
extern int __nfs_readpage_from_fscache(struct nfs_open_context *,
struct inode *, struct page *);
extern int __nfs_readpages_from_fscache(struct nfs_open_context *,
struct inode *, struct address_space *,
struct list_head *, unsigned *);
extern void __nfs_readpage_to_fscache(struct inode *, struct page *, int);
/*
* wait for a page to complete writing to the cache
*/
static inline void nfs_fscache_wait_on_page_write(struct nfs_inode *nfsi,
struct page *page)
{
if (PageFsCache(page))
fscache_wait_on_page_write(nfsi->fscache, page);
}
/*
* release the caching state associated with a page if undergoing complete page
* invalidation
*/
static inline void nfs_fscache_invalidate_page(struct page *page,
struct inode *inode)
{
if (PageFsCache(page))
__nfs_fscache_invalidate_page(page, inode);
}
/*
* Retrieve a page from an inode data storage object.
*/
static inline int nfs_readpage_from_fscache(struct nfs_open_context *ctx,
struct inode *inode,
struct page *page)
{
if (NFS_I(inode)->fscache)
return __nfs_readpage_from_fscache(ctx, inode, page);
return -ENOBUFS;
}
/*
* Retrieve a set of pages from an inode data storage object.
*/
static inline int nfs_readpages_from_fscache(struct nfs_open_context *ctx,
struct inode *inode,
struct address_space *mapping,
struct list_head *pages,
unsigned *nr_pages)
{
if (NFS_I(inode)->fscache)
return __nfs_readpages_from_fscache(ctx, inode, mapping, pages,
nr_pages);
return -ENOBUFS;
}
/*
* Store a page newly fetched from the server in an inode data storage object
* in the cache.
*/
static inline void nfs_readpage_to_fscache(struct inode *inode,
struct page *page,
int sync)
{
if (PageFsCache(page))
__nfs_readpage_to_fscache(inode, page, sync);
}
/*
* Invalidate the contents of fscache for this inode. This will not sleep.
*/
static inline void nfs_fscache_invalidate(struct inode *inode)
{
fscache_invalidate(NFS_I(inode)->fscache);
}
/*
* Wait for an object to finish being invalidated.
*/
static inline void nfs_fscache_wait_on_invalidate(struct inode *inode)
{
fscache_wait_on_invalidate(NFS_I(inode)->fscache);
}
/*
* indicate the client caching state as readable text
*/
static inline const char *nfs_server_fscache_state(struct nfs_server *server)
{
if (server->fscache && (server->options & NFS_OPTION_FSCACHE))
return "yes";
return "no ";
}
#else /* CONFIG_NFS_FSCACHE */
static inline int nfs_fscache_register(void) { return 0; }
static inline void nfs_fscache_unregister(void) {}
static inline void nfs_fscache_get_client_cookie(struct nfs_client *clp) {}
static inline void nfs_fscache_release_client_cookie(struct nfs_client *clp) {}
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 int nfs_fscache_release_page(struct page *page, gfp_t gfp)
{
return 1; /* True: may release page */
}
static inline void nfs_fscache_invalidate_page(struct page *page,
struct inode *inode) {}
static inline void nfs_fscache_wait_on_page_write(struct nfs_inode *nfsi,
struct page *page) {}
static inline int nfs_readpage_from_fscache(struct nfs_open_context *ctx,
struct inode *inode,
struct page *page)
{
return -ENOBUFS;
}
static inline int nfs_readpages_from_fscache(struct nfs_open_context *ctx,
struct inode *inode,
struct address_space *mapping,
struct list_head *pages,
unsigned *nr_pages)
{
return -ENOBUFS;
}
static inline void nfs_readpage_to_fscache(struct inode *inode,
struct page *page, int sync) {}
static inline void nfs_fscache_invalidate(struct inode *inode) {}
static inline void nfs_fscache_wait_on_invalidate(struct inode *inode) {}
static inline const char *nfs_server_fscache_state(struct nfs_server *server)
{
return "no ";
}
#endif /* CONFIG_NFS_FSCACHE */
#endif /* _NFS_FSCACHE_H */