Messages in this thread Patch in this message | | | Date | Thu, 20 Apr 2006 21:39:20 -0700 | From | Greg KH <> | Subject | [patch 18/22] Fix file lookup without ref |
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From: Dipankar Sarma <dipankar@in.ibm.com>
[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> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- drivers/char/tty_io.c | 8 ++++++-- fs/locks.c | 9 +++++++-- fs/proc/base.c | 21 +++++++++++++++------ 3 files changed, 28 insertions(+), 10 deletions(-)
--- linux-2.6.16.9.orig/drivers/char/tty_io.c +++ linux-2.6.16.9/drivers/char/tty_io.c @@ -2706,7 +2706,11 @@ 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); @@ -2721,7 +2725,7 @@ static void __do_SAK(void *arg) break; } } - rcu_read_unlock(); + spin_unlock(&p->files->file_lock); } task_unlock(p); } while_each_task_pid(session, PIDTYPE_SID, p); --- linux-2.6.16.9.orig/fs/locks.c +++ linux-2.6.16.9/fs/locks.c @@ -2212,7 +2212,12 @@ 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; @@ -2230,7 +2235,7 @@ void steal_locks(fl_owner_t from) set >>= 1; } } - rcu_read_unlock(); + spin_unlock(&files->file_lock); unlock_kernel(); } EXPORT_SYMBOL(steal_locks); --- linux-2.6.16.9.orig/fs/proc/base.c +++ linux-2.6.16.9/fs/proc/base.c @@ -294,16 +294,20 @@ static int proc_fd_link(struct inode *in 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; @@ -1485,7 +1489,12 @@ static struct dentry *proc_lookupfd(stru 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; @@ -1493,7 +1502,7 @@ static struct dentry *proc_lookupfd(stru 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; @@ -1503,7 +1512,7 @@ static struct dentry *proc_lookupfd(stru return NULL; out_unlock2: - rcu_read_unlock(); + spin_unlock(&files->file_lock); put_files_struct(files); out_unlock: iput(inode); -- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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