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authorJianyong Wu <jianyong.wu@arm.com>2020-09-23 17:11:46 +0300
committerDominique Martinet <asmadeus@codewreck.org>2020-11-19 19:20:39 +0300
commit6636b6dcc3db2258cd0585b8078c1c225c4b6dde (patch)
tree00d30096cadaafcee0cd79206fa0f6da315aa445 /fs/9p/fid.c
parent478ba09edc1f2f2ee27180a06150cb2d1a686f9c (diff)
downloadlinux-6636b6dcc3db2258cd0585b8078c1c225c4b6dde.tar.xz
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: 478ba09edc1f ("fs/9p: search open fids first") Signed-off-by: Jianyong Wu <jianyong.wu@arm.com> Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
Diffstat (limited to 'fs/9p/fid.c')
-rw-r--r--fs/9p/fid.c22
1 files changed, 18 insertions, 4 deletions
diff --git a/fs/9p/fid.c b/fs/9p/fid.c
index 0b23b0fe6c51..89643dabcdae 100644
--- a/fs/9p/fid.c
+++ b/fs/9p/fid.c
@@ -28,6 +28,7 @@
static inline void __add_fid(struct dentry *dentry, struct p9_fid *fid)
{
+ atomic_set(&fid->count, 1);
hlist_add_head(&fid->dlist, (struct hlist_head *)&dentry->d_fsdata);
}
@@ -60,6 +61,8 @@ static struct p9_fid *v9fs_fid_find_inode(struct inode *inode, kuid_t uid)
break;
}
}
+ if (ret && !IS_ERR(ret))
+ atomic_inc(&ret->count);
spin_unlock(&inode->i_lock);
return ret;
}
@@ -74,6 +77,7 @@ static struct p9_fid *v9fs_fid_find_inode(struct inode *inode, kuid_t uid)
void v9fs_open_fid_add(struct inode *inode, struct p9_fid *fid)
{
spin_lock(&inode->i_lock);
+ atomic_set(&fid->count, 1);
hlist_add_head(&fid->ilist, (struct hlist_head *)&inode->i_private);
spin_unlock(&inode->i_lock);
}
@@ -106,6 +110,7 @@ static struct p9_fid *v9fs_fid_find(struct dentry *dentry, kuid_t uid, int any)
hlist_for_each_entry(fid, h, dlist) {
if (any || uid_eq(fid->uid, uid)) {
ret = fid;
+ atomic_inc(&ret->count);
break;
}
}
@@ -167,7 +172,10 @@ static struct p9_fid *v9fs_fid_lookup_with_uid(struct dentry *dentry,
fid = v9fs_fid_find(ds, uid, any);
if (fid) {
/* Found the parent fid do a lookup with that */
- fid = p9_client_walk(fid, 1, &dentry->d_name.name, 1);
+ struct p9_fid *ofid = fid;
+
+ fid = p9_client_walk(ofid, 1, &dentry->d_name.name, 1);
+ p9_client_clunk(ofid);
goto fid_out;
}
up_read(&v9ses->rename_sem);
@@ -192,8 +200,10 @@ static struct p9_fid *v9fs_fid_lookup_with_uid(struct dentry *dentry,
v9fs_fid_add(dentry->d_sb->s_root, fid);
}
/* If we are root ourself just return that */
- if (dentry->d_sb->s_root == dentry)
+ if (dentry->d_sb->s_root == dentry) {
+ atomic_inc(&fid->count);
return fid;
+ }
/*
* Do a multipath walk with attached root.
* When walking parent we need to make sure we
@@ -240,6 +250,7 @@ fid_out:
fid = ERR_PTR(-ENOENT);
} else {
__add_fid(dentry, fid);
+ atomic_inc(&fid->count);
spin_unlock(&dentry->d_lock);
}
}
@@ -290,11 +301,14 @@ struct p9_fid *v9fs_fid_lookup(struct dentry *dentry)
struct p9_fid *v9fs_writeback_fid(struct dentry *dentry)
{
int err;
- struct p9_fid *fid;
+ struct p9_fid *fid, *ofid;
- fid = clone_fid(v9fs_fid_lookup_with_uid(dentry, GLOBAL_ROOT_UID, 0));
+ ofid = v9fs_fid_lookup_with_uid(dentry, GLOBAL_ROOT_UID, 0);
+ if (ofid && !IS_ERR(ofid))
+ fid = clone_fid(ofid);
if (IS_ERR(fid))
goto error_out;
+ p9_client_clunk(ofid);
/*
* writeback fid will only be used to write back the
* dirty pages. We always request for the open fid in read-write