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6636b6dcc3
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>
109 lines
2.5 KiB
C
109 lines
2.5 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* linux/fs/9p/vfs_dentry.c
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*
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* This file contians vfs dentry 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/pagemap.h>
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#include <linux/stat.h>
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#include <linux/string.h>
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#include <linux/inet.h>
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#include <linux/namei.h>
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#include <linux/idr.h>
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#include <linux/sched.h>
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#include <linux/slab.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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* v9fs_cached_dentry_delete - called when dentry refcount equals 0
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* @dentry: dentry in question
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*
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*/
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static int v9fs_cached_dentry_delete(const struct dentry *dentry)
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{
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p9_debug(P9_DEBUG_VFS, " dentry: %pd (%p)\n",
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dentry, dentry);
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/* Don't cache negative dentries */
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if (d_really_is_negative(dentry))
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return 1;
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return 0;
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}
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/**
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* v9fs_dentry_release - called when dentry is going to be freed
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* @dentry: dentry that is being release
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*
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*/
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static void v9fs_dentry_release(struct dentry *dentry)
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{
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struct hlist_node *p, *n;
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p9_debug(P9_DEBUG_VFS, " dentry: %pd (%p)\n",
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dentry, dentry);
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hlist_for_each_safe(p, n, (struct hlist_head *)&dentry->d_fsdata)
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p9_client_clunk(hlist_entry(p, struct p9_fid, dlist));
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dentry->d_fsdata = NULL;
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}
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static int v9fs_lookup_revalidate(struct dentry *dentry, unsigned int flags)
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{
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struct p9_fid *fid;
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struct inode *inode;
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struct v9fs_inode *v9inode;
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if (flags & LOOKUP_RCU)
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return -ECHILD;
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inode = d_inode(dentry);
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if (!inode)
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goto out_valid;
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v9inode = V9FS_I(inode);
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if (v9inode->cache_validity & V9FS_INO_INVALID_ATTR) {
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int retval;
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struct v9fs_session_info *v9ses;
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fid = v9fs_fid_lookup(dentry);
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if (IS_ERR(fid))
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return PTR_ERR(fid);
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v9ses = v9fs_inode2v9ses(inode);
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if (v9fs_proto_dotl(v9ses))
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retval = v9fs_refresh_inode_dotl(fid, inode);
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else
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retval = v9fs_refresh_inode(fid, inode);
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p9_client_clunk(fid);
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if (retval == -ENOENT)
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return 0;
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if (retval < 0)
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return retval;
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}
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out_valid:
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return 1;
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}
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const struct dentry_operations v9fs_cached_dentry_operations = {
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.d_revalidate = v9fs_lookup_revalidate,
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.d_weak_revalidate = v9fs_lookup_revalidate,
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.d_delete = v9fs_cached_dentry_delete,
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.d_release = v9fs_dentry_release,
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};
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const struct dentry_operations v9fs_dentry_operations = {
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.d_delete = always_delete_dentry,
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.d_release = v9fs_dentry_release,
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};
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