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![Jianyong Wu](/assets/img/avatar_default.png)
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>
237 lines
4.9 KiB
C
237 lines
4.9 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* linux/fs/9p/vfs_dir.c
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*
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* This file contains vfs directory ops for the 9P2000 protocol.
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*
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* Copyright (C) 2004 by Eric Van Hensbergen <ericvh@gmail.com>
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* Copyright (C) 2002 by Ron Minnich <rminnich@lanl.gov>
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*/
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#include <linux/module.h>
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#include <linux/errno.h>
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#include <linux/fs.h>
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#include <linux/file.h>
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#include <linux/stat.h>
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#include <linux/string.h>
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#include <linux/sched.h>
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#include <linux/inet.h>
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#include <linux/idr.h>
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#include <linux/slab.h>
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#include <linux/uio.h>
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#include <net/9p/9p.h>
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#include <net/9p/client.h>
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#include "v9fs.h"
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#include "v9fs_vfs.h"
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#include "fid.h"
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/**
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* struct p9_rdir - readdir accounting
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* @head: start offset of current dirread buffer
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* @tail: end offset of current dirread buffer
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* @buf: dirread buffer
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*
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* private structure for keeping track of readdir
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* allocated on demand
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*/
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struct p9_rdir {
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int head;
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int tail;
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uint8_t buf[];
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};
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/**
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* dt_type - return file type
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* @mistat: mistat structure
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*
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*/
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static inline int dt_type(struct p9_wstat *mistat)
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{
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unsigned long perm = mistat->mode;
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int rettype = DT_REG;
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if (perm & P9_DMDIR)
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rettype = DT_DIR;
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if (perm & P9_DMSYMLINK)
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rettype = DT_LNK;
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return rettype;
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}
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/**
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* v9fs_alloc_rdir_buf - Allocate buffer used for read and readdir
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* @filp: opened file structure
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* @buflen: Length in bytes of buffer to allocate
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*
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*/
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static struct p9_rdir *v9fs_alloc_rdir_buf(struct file *filp, int buflen)
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{
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struct p9_fid *fid = filp->private_data;
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if (!fid->rdir)
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fid->rdir = kzalloc(sizeof(struct p9_rdir) + buflen, GFP_KERNEL);
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return fid->rdir;
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}
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/**
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* v9fs_dir_readdir - iterate through a directory
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* @file: opened file structure
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* @ctx: actor we feed the entries to
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*
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*/
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static int v9fs_dir_readdir(struct file *file, struct dir_context *ctx)
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{
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bool over;
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struct p9_wstat st;
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int err = 0;
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struct p9_fid *fid;
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int buflen;
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struct p9_rdir *rdir;
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struct kvec kvec;
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p9_debug(P9_DEBUG_VFS, "name %pD\n", file);
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fid = file->private_data;
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buflen = fid->clnt->msize - P9_IOHDRSZ;
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rdir = v9fs_alloc_rdir_buf(file, buflen);
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if (!rdir)
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return -ENOMEM;
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kvec.iov_base = rdir->buf;
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kvec.iov_len = buflen;
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while (1) {
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if (rdir->tail == rdir->head) {
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struct iov_iter to;
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int n;
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iov_iter_kvec(&to, READ, &kvec, 1, buflen);
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n = p9_client_read(file->private_data, ctx->pos, &to,
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&err);
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if (err)
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return err;
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if (n == 0)
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return 0;
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rdir->head = 0;
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rdir->tail = n;
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}
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while (rdir->head < rdir->tail) {
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err = p9stat_read(fid->clnt, rdir->buf + rdir->head,
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rdir->tail - rdir->head, &st);
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if (err <= 0) {
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p9_debug(P9_DEBUG_VFS, "returned %d\n", err);
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return -EIO;
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}
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over = !dir_emit(ctx, st.name, strlen(st.name),
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v9fs_qid2ino(&st.qid), dt_type(&st));
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p9stat_free(&st);
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if (over)
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return 0;
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rdir->head += err;
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ctx->pos += err;
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}
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}
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}
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/**
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* v9fs_dir_readdir_dotl - iterate through a directory
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* @file: opened file structure
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* @ctx: actor we feed the entries to
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*
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*/
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static int v9fs_dir_readdir_dotl(struct file *file, struct dir_context *ctx)
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{
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int err = 0;
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struct p9_fid *fid;
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int buflen;
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struct p9_rdir *rdir;
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struct p9_dirent curdirent;
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p9_debug(P9_DEBUG_VFS, "name %pD\n", file);
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fid = file->private_data;
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buflen = fid->clnt->msize - P9_READDIRHDRSZ;
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rdir = v9fs_alloc_rdir_buf(file, buflen);
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if (!rdir)
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return -ENOMEM;
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while (1) {
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if (rdir->tail == rdir->head) {
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err = p9_client_readdir(fid, rdir->buf, buflen,
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ctx->pos);
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if (err <= 0)
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return err;
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rdir->head = 0;
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rdir->tail = err;
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}
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while (rdir->head < rdir->tail) {
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err = p9dirent_read(fid->clnt, rdir->buf + rdir->head,
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rdir->tail - rdir->head,
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&curdirent);
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if (err < 0) {
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p9_debug(P9_DEBUG_VFS, "returned %d\n", err);
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return -EIO;
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}
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if (!dir_emit(ctx, curdirent.d_name,
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strlen(curdirent.d_name),
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v9fs_qid2ino(&curdirent.qid),
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curdirent.d_type))
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return 0;
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ctx->pos = curdirent.d_off;
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rdir->head += err;
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}
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}
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}
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/**
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* v9fs_dir_release - close a directory
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* @inode: inode of the directory
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* @filp: file pointer to a directory
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*
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*/
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int v9fs_dir_release(struct inode *inode, struct file *filp)
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{
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struct p9_fid *fid;
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fid = filp->private_data;
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p9_debug(P9_DEBUG_VFS, "inode: %p filp: %p fid: %d\n",
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inode, filp, fid ? fid->fid : -1);
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if (fid) {
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spin_lock(&inode->i_lock);
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hlist_del(&fid->ilist);
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spin_unlock(&inode->i_lock);
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p9_client_clunk(fid);
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}
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return 0;
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}
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const struct file_operations v9fs_dir_operations = {
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.read = generic_read_dir,
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.llseek = generic_file_llseek,
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.iterate_shared = v9fs_dir_readdir,
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.open = v9fs_file_open,
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.release = v9fs_dir_release,
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};
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const struct file_operations v9fs_dir_operations_dotl = {
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.read = generic_read_dir,
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.llseek = generic_file_llseek,
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.iterate_shared = v9fs_dir_readdir_dotl,
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.open = v9fs_file_open,
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.release = v9fs_dir_release,
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.fsync = v9fs_file_fsync_dotl,
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};
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