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[PATCH] Fix file lookup without ref

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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>
This commit is contained in:
Dipankar Sarma 2006-04-18 22:21:46 -07:00 committed by Linus Torvalds
parent fb30d64568
commit ca99c1da08
3 changed files with 28 additions and 10 deletions
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8
drivers/char/tty_io.c
View File

@ -2723,7 +2723,11 @@ static void __do_SAK(void *arg)
}
task_lock(p);
if (p->files) {
rcu_read_lock();
/*
* We don't take a ref to the file, so we must
* hold ->file_lock instead.
*/
spin_lock(&p->files->file_lock);
fdt = files_fdtable(p->files);
for (i=0; i < fdt->max_fds; i++) {
filp = fcheck_files(p->files, i);
@ -2738,7 +2742,7 @@ static void __do_SAK(void *arg)
break;
}
}
rcu_read_unlock();
spin_unlock(&p->files->file_lock);
}
task_unlock(p);
} while_each_thread(g, p);

9
fs/locks.c
View File

@ -2230,7 +2230,12 @@ void steal_locks(fl_owner_t from)
lock_kernel();
j = 0;
rcu_read_lock();
/*
* We are not taking a ref to the file structures, so
* we need to acquire ->file_lock.
*/
spin_lock(&files->file_lock);
fdt = files_fdtable(files);
for (;;) {
unsigned long set;
@ -2248,7 +2253,7 @@ void steal_locks(fl_owner_t from)
set >>= 1;
}
}
rcu_read_unlock();
spin_unlock(&files->file_lock);
unlock_kernel();
}
EXPORT_SYMBOL(steal_locks);

21
fs/proc/base.c
View File

@ -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);