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authorDipankar Sarma <dipankar@in.ibm.com>2006-04-18 22:21:46 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2006-04-19 09:13:51 -0700
commitca99c1da080345e227cfb083c330a184d42e27f3 (patch)
treee417b4c456ae31dc1dde8027b6be44a1a9f19395 /fs/proc
parentfb30d64568fd8f6a21afef987f11852a109723da (diff)
[PATCH] Fix file lookup without ref
There are places in the kernel where we look up files in fd tables and access the file structure without holding refereces to the file. So, we need special care to avoid the race between looking up files in the fd table and tearing down of the file in another CPU. Otherwise, one might see a NULL f_dentry or such torn down version of the file. This patch fixes those special places where such a race may happen. Signed-off-by: Dipankar Sarma <dipankar@in.ibm.com> Acked-by: "Paul E. McKenney" <paulmck@us.ibm.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'fs/proc')
-rw-r--r--fs/proc/base.c21
1 files changed, 15 insertions, 6 deletions
diff --git a/fs/proc/base.c b/fs/proc/base.c
index a3a3eecef68..6cc77dc3f3f 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -297,16 +297,20 @@ static int proc_fd_link(struct inode *inode, struct dentry **dentry, struct vfsm
files = get_files_struct(task);
if (files) {
- rcu_read_lock();
+ /*
+ * We are not taking a ref to the file structure, so we must
+ * hold ->file_lock.
+ */
+ spin_lock(&files->file_lock);
file = fcheck_files(files, fd);
if (file) {
*mnt = mntget(file->f_vfsmnt);
*dentry = dget(file->f_dentry);
- rcu_read_unlock();
+ spin_unlock(&files->file_lock);
put_files_struct(files);
return 0;
}
- rcu_read_unlock();
+ spin_unlock(&files->file_lock);
put_files_struct(files);
}
return -ENOENT;
@@ -1523,7 +1527,12 @@ static struct dentry *proc_lookupfd(struct inode * dir, struct dentry * dentry,
if (!files)
goto out_unlock;
inode->i_mode = S_IFLNK;
- rcu_read_lock();
+
+ /*
+ * We are not taking a ref to the file structure, so we must
+ * hold ->file_lock.
+ */
+ spin_lock(&files->file_lock);
file = fcheck_files(files, fd);
if (!file)
goto out_unlock2;
@@ -1531,7 +1540,7 @@ static struct dentry *proc_lookupfd(struct inode * dir, struct dentry * dentry,
inode->i_mode |= S_IRUSR | S_IXUSR;
if (file->f_mode & 2)
inode->i_mode |= S_IWUSR | S_IXUSR;
- rcu_read_unlock();
+ spin_unlock(&files->file_lock);
put_files_struct(files);
inode->i_op = &proc_pid_link_inode_operations;
inode->i_size = 64;
@@ -1541,7 +1550,7 @@ static struct dentry *proc_lookupfd(struct inode * dir, struct dentry * dentry,
return NULL;
out_unlock2:
- rcu_read_unlock();
+ spin_unlock(&files->file_lock);
put_files_struct(files);
out_unlock:
iput(inode);