[PATCH] autofs4 deadlock during expire - kernel 2.6

Ian Kent
2003-09-23T13:41:37Z

I have noticed that a deadlock can occur in the autofs4 module in the 2.6
kernel and RedHat kernels with the O(1) scheduler patch. The easiest way
to reproduce it is with an autofs-4.0.0 tree mount with at least 10 mounts
within a Nautilus desktop environment with the module debug flag set.
Perhaps this is because of the longish amount of time spent in the expire
state.

The scenario:

1) An expire locates an expirable dentry and signals the user space
daemon to umount it.
2) During the umount operation Nautilus notices and scans entries in the
directory tree triggering a revalidate/lookup.
3) autofs4 places the requesting process on the umount wait queue.
4) At completion of the expire both process are released from the wait
queue.
5) If the lookup gets a quantum first deadlock occurs and expiration stops
leaving an autofs mount that is permanently busy.

The following patch fixes this by ensuring that the expire gets a lookin
before the revalidate/lookup continues.

The problem of the remount that this causes remains and I an not sure how
to deal with that at this stage.

Comments and suggestions please.

Is this acceptable for inclusion in the kernel?
If so what should I do to make this happen?

diff -Nur autofs4-2.6.orig/fs/autofs4/autofs_i.h autofs4-2.6.deadlock/fs/autofs4/autofs_i.h
--- autofs4-2.6.orig/fs/autofs4/autofs_i.h 2003-09-09 03:50:14.000000000 +0800
+++ autofs4-2.6.deadlock/fs/autofs4/autofs_i.h 2003-09-22 22:48:11.000000000 +0800
@@ -82,6 +82,7 @@
char *name;
/* This is for status reporting upon return */
int status;
+ struct task_struct *owner;
int wait_ctr;
};

diff -Nur autofs4-2.6.orig/fs/autofs4/waitq.c autofs4-2.6.deadlock/fs/autofs4/waitq.c
--- autofs4-2.6.orig/fs/autofs4/waitq.c 2003-09-09 03:50:31.000000000 +0800
+++ autofs4-2.6.deadlock/fs/autofs4/waitq.c 2003-09-23 00:02:29.209789432 +0800
@@ -206,6 +206,11 @@

interruptible_sleep_on(&wq->queue);

+ if (waitqueue_active(&wq->queue) && current != wq->owner) {
+ set_current_state(TASK_INTERRUPTIBLE);
+ schedule_timeout(wq->wait_ctr * (HZ/10));
+ }
+
spin_lock_irqsave(&current->sighand->siglock, irqflags);
current->blocked = oldset;
recalc_sigpending();