Andrey Borzenkov <arvidjaar@xxxxxxx> wrote:
>
> When devfs_lookup needs to call devfsd it arranges for other lookups for the
> same name to wait. It is using local variable as wait queue head. After
> devfsd returns devfs_lookup wakes up all waiters and returns. Unfortunately
> there is no garantee all waiters will actually get chance to run and clean
> up
> before devfs_lookup returns. so some of them attempt to access already freed
> storage on stack.
OK, but I think there is a simpler fix. We can rely on the side-effects of
prepare_to_wait() and finish_wait().
The wakeup() will remove all wait_queue_t's from the wait_queue_head, and
so when the waiters wake up and call finish_wait(), they will never touch
the now-out-of-scope waitqueue head.
It is a little faster than the currentcode, too.
Could you please test this?
diff -puN fs/devfs/base.c~devfs-oops-fix-2 fs/devfs/base.c
--- 25/fs/devfs/base.c~devfs-oops-fix-2 2003-07-06 11:55:38.000000000 -0700
+++ 25-akpm/fs/devfs/base.c 2003-07-06 11:59:23.000000000 -0700
@@ -2218,7 +2218,6 @@ static int devfs_d_revalidate_wait (stru
struct fs_info *fs_info = dir->i_sb->s_fs_info;
devfs_handle_t parent = get_devfs_entry_from_vfs_inode (dir);
struct devfs_lookup_struct *lookup_info = dentry->d_fsdata;
- DECLARE_WAITQUEUE (wait, current);
if ( is_devfsd_or_child (fs_info) )
{
@@ -2252,11 +2251,12 @@ static int devfs_d_revalidate_wait (stru
read_lock (&parent->u.dir.lock);
if (dentry->d_fsdata)
{
- set_current_state (TASK_UNINTERRUPTIBLE);
- add_wait_queue (&lookup_info->wait_queue, &wait);
- read_unlock (&parent->u.dir.lock);
- schedule ();
- remove_wait_queue (&lookup_info->wait_queue, &wait);
+ DEFINE_WAIT(wait);
+
+ prepare_to_wait(&lookup_info->wait_queue, &wait, TASK_UNINTERRUPTIBLE);
+ read_unlock(&parent->u.dir.lock);
+ schedule();
+ finish_wait(&lookup_info->wait_queue, &wait);
}
else read_unlock (&parent->u.dir.lock);
return 1;
@@ -2336,6 +2336,12 @@ out:
dentry->d_op = &devfs_dops;
dentry->d_fsdata = NULL;
write_lock (&parent->u.dir.lock);
+ /*
+ * This wakeup will remove all waiters' wait_queue_t's from the waitqueue
+ * head, because the waiters use prepare_to_wait()/finished_wait().
+ * Hence it is OK that the waitqueue_head goes out of scope immediately
+ * after the wakeup is delivered
+ */
wake_up (&lookup_info.wait_queue);
write_unlock (&parent->u.dir.lock);
devfs_put (de);
_
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