Re: fs: WARNING in locks_unlink_lock_ctx (not holding proper lock)

[Peter Zijlstra <peterz@infradead.org>]

On Fri, Oct 07, 2016 at 07:26:36PM -0400, Jeff Layton wrote:

> Well spotted. Yeah, I think you're right. The assertion is this:
> 
>     percpu_rwsem_assert_held(&file_rwsem);
> 
> I'm guessing this is probably fallout from the lglock to rwsem
> conversion (commit aba376607383).
> 
> From a quick glance, I think we probably just need to down_read the
> file_rwsem in locks_remove_lease, prior to taking the flc_lock, and
> release it just afterward.

Correct on all that.

> I do want to go over the code a little more
> closely though to make sure other codepaths aren't missing that lock
> though.

Urg, sorry for missing these, I went through it again and found the
below to be missing.

---
Subject: fs/locks: Add missing file_sem locks

I overlooked a few code-paths that can lead to
locks_delete_global_locks().

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---

diff --git a/fs/locks.c b/fs/locks.c
index 133fb2543d21..c623490863a9 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1604,6 +1604,7 @@ int fcntl_getlease(struct file *filp)
 
 	ctx = smp_load_acquire(&inode->i_flctx);
 	if (ctx && !list_empty_careful(&ctx->flc_lease)) {
+		percpu_down_read_preempt_disable(&file_rwsem);
 		spin_lock(&ctx->flc_lock);
 		time_out_leases(file_inode(filp), &dispose);
 		list_for_each_entry(fl, &ctx->flc_lease, fl_list) {
@@ -1613,6 +1614,8 @@ int fcntl_getlease(struct file *filp)
 			break;
 		}
 		spin_unlock(&ctx->flc_lock);
+		percpu_up_read_preempt_enable(&file_rwsem);
+
 		locks_dispose_list(&dispose);
 	}
 	return type;
@@ -2522,11 +2525,14 @@ locks_remove_lease(struct file *filp, struct file_lock_context *ctx)
 	if (list_empty(&ctx->flc_lease))
 		return;
 
+	percpu_down_read_preempt_disable(&file_rwsem);
 	spin_lock(&ctx->flc_lock);
 	list_for_each_entry_safe(fl, tmp, &ctx->flc_lease, fl_list)
 		if (filp == fl->fl_file)
 			lease_modify(fl, F_UNLCK, &dispose);
 	spin_unlock(&ctx->flc_lock);
+	percpu_up_read_preempt_enable(&file_rwsem);
+
 	locks_dispose_list(&dispose);
 }