linux/fs/9p/vfs_super.c
Jianyong Wu 6636b6dcc3 9p: add refcount to p9_fid struct
Fix race issue in fid contention.

Eric's and Greg's patch offer a mechanism to fix open-unlink-f*syscall
bug in 9p. But there is race issue in fid parallel accesses.
As Greg's patch stores all of fids from opened files into according inode,
so all the lookup fid ops can retrieve fid from inode preferentially. But
there is no mechanism to handle the fid contention issue. For example,
there are two threads get the same fid in the same time and one of them
clunk the fid before the other thread ready to discard the fid. In this
scenario, it will lead to some fatal problems, even kernel core dump.

I introduce a mechanism to fix this race issue. A counter field introduced
into p9_fid struct to store the reference counter to the fid. When a fid
is allocated from the inode or dentry, the counter will increase, and
will decrease at the end of its occupation. It is guaranteed that the
fid won't be clunked before the reference counter go down to 0, then
we can avoid the clunked fid to be used.

tests:
race issue test from the old test case:
for file in {01..50}; do touch f.${file}; done
seq 1 1000 | xargs -n 1 -P 50 -I{} cat f.* > /dev/null

open-unlink-f*syscall test:
I have tested for f*syscall include: ftruncate fstat fchown fchmod faccessat.

Link: http://lkml.kernel.org/r/20200923141146.90046-5-jianyong.wu@arm.com
Fixes: 478ba09edc ("fs/9p: search open fids first")
Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
2020-11-19 17:20:39 +01:00

365 lines
8.0 KiB
C

// SPDX-License-Identifier: GPL-2.0-only
/*
* linux/fs/9p/vfs_super.c
*
* This file contians superblock ops for 9P2000. It is intended that
* you mount this file system on directories.
*
* Copyright (C) 2004 by Eric Van Hensbergen <ericvh@gmail.com>
* Copyright (C) 2002 by Ron Minnich <rminnich@lanl.gov>
*/
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/errno.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/stat.h>
#include <linux/string.h>
#include <linux/inet.h>
#include <linux/pagemap.h>
#include <linux/mount.h>
#include <linux/idr.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/statfs.h>
#include <linux/magic.h>
#include <net/9p/9p.h>
#include <net/9p/client.h>
#include "v9fs.h"
#include "v9fs_vfs.h"
#include "fid.h"
#include "xattr.h"
#include "acl.h"
static const struct super_operations v9fs_super_ops, v9fs_super_ops_dotl;
/**
* v9fs_set_super - set the superblock
* @s: super block
* @data: file system specific data
*
*/
static int v9fs_set_super(struct super_block *s, void *data)
{
s->s_fs_info = data;
return set_anon_super(s, data);
}
/**
* v9fs_fill_super - populate superblock with info
* @sb: superblock
* @v9ses: session information
* @flags: flags propagated from v9fs_mount()
*
*/
static int
v9fs_fill_super(struct super_block *sb, struct v9fs_session_info *v9ses,
int flags)
{
int ret;
sb->s_maxbytes = MAX_LFS_FILESIZE;
sb->s_blocksize_bits = fls(v9ses->maxdata - 1);
sb->s_blocksize = 1 << sb->s_blocksize_bits;
sb->s_magic = V9FS_MAGIC;
if (v9fs_proto_dotl(v9ses)) {
sb->s_op = &v9fs_super_ops_dotl;
sb->s_xattr = v9fs_xattr_handlers;
} else {
sb->s_op = &v9fs_super_ops;
sb->s_time_max = U32_MAX;
}
sb->s_time_min = 0;
ret = super_setup_bdi(sb);
if (ret)
return ret;
if (!v9ses->cache) {
sb->s_bdi->ra_pages = 0;
sb->s_bdi->io_pages = 0;
}
sb->s_flags |= SB_ACTIVE | SB_DIRSYNC;
if (!v9ses->cache)
sb->s_flags |= SB_SYNCHRONOUS;
#ifdef CONFIG_9P_FS_POSIX_ACL
if ((v9ses->flags & V9FS_ACL_MASK) == V9FS_POSIX_ACL)
sb->s_flags |= SB_POSIXACL;
#endif
return 0;
}
/**
* v9fs_mount - mount a superblock
* @fs_type: file system type
* @flags: mount flags
* @dev_name: device name that was mounted
* @data: mount options
*
*/
static struct dentry *v9fs_mount(struct file_system_type *fs_type, int flags,
const char *dev_name, void *data)
{
struct super_block *sb = NULL;
struct inode *inode = NULL;
struct dentry *root = NULL;
struct v9fs_session_info *v9ses = NULL;
umode_t mode = S_IRWXUGO | S_ISVTX;
struct p9_fid *fid;
int retval = 0;
p9_debug(P9_DEBUG_VFS, "\n");
v9ses = kzalloc(sizeof(struct v9fs_session_info), GFP_KERNEL);
if (!v9ses)
return ERR_PTR(-ENOMEM);
fid = v9fs_session_init(v9ses, dev_name, data);
if (IS_ERR(fid)) {
retval = PTR_ERR(fid);
goto free_session;
}
sb = sget(fs_type, NULL, v9fs_set_super, flags, v9ses);
if (IS_ERR(sb)) {
retval = PTR_ERR(sb);
goto clunk_fid;
}
retval = v9fs_fill_super(sb, v9ses, flags);
if (retval)
goto release_sb;
if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
sb->s_d_op = &v9fs_cached_dentry_operations;
else
sb->s_d_op = &v9fs_dentry_operations;
inode = v9fs_get_inode(sb, S_IFDIR | mode, 0);
if (IS_ERR(inode)) {
retval = PTR_ERR(inode);
goto release_sb;
}
root = d_make_root(inode);
if (!root) {
retval = -ENOMEM;
goto release_sb;
}
sb->s_root = root;
if (v9fs_proto_dotl(v9ses)) {
struct p9_stat_dotl *st = NULL;
st = p9_client_getattr_dotl(fid, P9_STATS_BASIC);
if (IS_ERR(st)) {
retval = PTR_ERR(st);
goto release_sb;
}
d_inode(root)->i_ino = v9fs_qid2ino(&st->qid);
v9fs_stat2inode_dotl(st, d_inode(root), 0);
kfree(st);
} else {
struct p9_wstat *st = NULL;
st = p9_client_stat(fid);
if (IS_ERR(st)) {
retval = PTR_ERR(st);
goto release_sb;
}
d_inode(root)->i_ino = v9fs_qid2ino(&st->qid);
v9fs_stat2inode(st, d_inode(root), sb, 0);
p9stat_free(st);
kfree(st);
}
retval = v9fs_get_acl(inode, fid);
if (retval)
goto release_sb;
v9fs_fid_add(root, fid);
p9_debug(P9_DEBUG_VFS, " simple set mount, return 0\n");
return dget(sb->s_root);
clunk_fid:
p9_client_clunk(fid);
v9fs_session_close(v9ses);
free_session:
kfree(v9ses);
return ERR_PTR(retval);
release_sb:
/*
* we will do the session_close and root dentry release
* in the below call. But we need to clunk fid, because we haven't
* attached the fid to dentry so it won't get clunked
* automatically.
*/
p9_client_clunk(fid);
deactivate_locked_super(sb);
return ERR_PTR(retval);
}
/**
* v9fs_kill_super - Kill Superblock
* @s: superblock
*
*/
static void v9fs_kill_super(struct super_block *s)
{
struct v9fs_session_info *v9ses = s->s_fs_info;
p9_debug(P9_DEBUG_VFS, " %p\n", s);
kill_anon_super(s);
v9fs_session_cancel(v9ses);
v9fs_session_close(v9ses);
kfree(v9ses);
s->s_fs_info = NULL;
p9_debug(P9_DEBUG_VFS, "exiting kill_super\n");
}
static void
v9fs_umount_begin(struct super_block *sb)
{
struct v9fs_session_info *v9ses;
v9ses = sb->s_fs_info;
v9fs_session_begin_cancel(v9ses);
}
static int v9fs_statfs(struct dentry *dentry, struct kstatfs *buf)
{
struct v9fs_session_info *v9ses;
struct p9_fid *fid;
struct p9_rstatfs rs;
int res;
fid = v9fs_fid_lookup(dentry);
if (IS_ERR(fid)) {
res = PTR_ERR(fid);
goto done;
}
v9ses = v9fs_dentry2v9ses(dentry);
if (v9fs_proto_dotl(v9ses)) {
res = p9_client_statfs(fid, &rs);
if (res == 0) {
buf->f_type = rs.type;
buf->f_bsize = rs.bsize;
buf->f_blocks = rs.blocks;
buf->f_bfree = rs.bfree;
buf->f_bavail = rs.bavail;
buf->f_files = rs.files;
buf->f_ffree = rs.ffree;
buf->f_fsid = u64_to_fsid(rs.fsid);
buf->f_namelen = rs.namelen;
}
if (res != -ENOSYS)
goto done;
}
res = simple_statfs(dentry, buf);
done:
p9_client_clunk(fid);
return res;
}
static int v9fs_drop_inode(struct inode *inode)
{
struct v9fs_session_info *v9ses;
v9ses = v9fs_inode2v9ses(inode);
if (v9ses->cache == CACHE_LOOSE || v9ses->cache == CACHE_FSCACHE)
return generic_drop_inode(inode);
/*
* in case of non cached mode always drop the
* the inode because we want the inode attribute
* to always match that on the server.
*/
return 1;
}
static int v9fs_write_inode(struct inode *inode,
struct writeback_control *wbc)
{
int ret;
struct p9_wstat wstat;
struct v9fs_inode *v9inode;
/*
* send an fsync request to server irrespective of
* wbc->sync_mode.
*/
p9_debug(P9_DEBUG_VFS, "%s: inode %p\n", __func__, inode);
v9inode = V9FS_I(inode);
if (!v9inode->writeback_fid)
return 0;
v9fs_blank_wstat(&wstat);
ret = p9_client_wstat(v9inode->writeback_fid, &wstat);
if (ret < 0) {
__mark_inode_dirty(inode, I_DIRTY_DATASYNC);
return ret;
}
return 0;
}
static int v9fs_write_inode_dotl(struct inode *inode,
struct writeback_control *wbc)
{
int ret;
struct v9fs_inode *v9inode;
/*
* send an fsync request to server irrespective of
* wbc->sync_mode.
*/
v9inode = V9FS_I(inode);
p9_debug(P9_DEBUG_VFS, "%s: inode %p, writeback_fid %p\n",
__func__, inode, v9inode->writeback_fid);
if (!v9inode->writeback_fid)
return 0;
ret = p9_client_fsync(v9inode->writeback_fid, 0);
if (ret < 0) {
__mark_inode_dirty(inode, I_DIRTY_DATASYNC);
return ret;
}
return 0;
}
static const struct super_operations v9fs_super_ops = {
.alloc_inode = v9fs_alloc_inode,
.free_inode = v9fs_free_inode,
.statfs = simple_statfs,
.evict_inode = v9fs_evict_inode,
.show_options = v9fs_show_options,
.umount_begin = v9fs_umount_begin,
.write_inode = v9fs_write_inode,
};
static const struct super_operations v9fs_super_ops_dotl = {
.alloc_inode = v9fs_alloc_inode,
.free_inode = v9fs_free_inode,
.statfs = v9fs_statfs,
.drop_inode = v9fs_drop_inode,
.evict_inode = v9fs_evict_inode,
.show_options = v9fs_show_options,
.umount_begin = v9fs_umount_begin,
.write_inode = v9fs_write_inode_dotl,
};
struct file_system_type v9fs_fs_type = {
.name = "9p",
.mount = v9fs_mount,
.kill_sb = v9fs_kill_super,
.owner = THIS_MODULE,
.fs_flags = FS_RENAME_DOES_D_MOVE,
};
MODULE_ALIAS_FS("9p");