Commit 81be24d2 authored Jun 03, 2017 by Al Viro Committed by Al Viro Jun 15, 2017

Hang/soft lockup in d_invalidate with simultaneous calls



It's not hard to trigger a bunch of d_invalidate() on the same
dentry in parallel.  They end up fighting each other - any
dentry picked for removal by one will be skipped by the rest
and we'll go for the next iteration through the entire
subtree, even if everything is being skipped.  Morevoer, we
immediately go back to scanning the subtree.  The only thing
we really need is to dissolve all mounts in the subtree and
as soon as we've nothing left to do, we can just unhash the
dentry and bugger off.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

parent 32c1431e

fs/dcache.c

+4 −6

Original line number	Diff line number	Diff line
		@@ -1494,7 +1494,7 @@ static void check_and_drop(void *_data)
		{
		struct detach_data *data = _data;

		if (!data->mountpoint && !data->select.found)
		if (!data->mountpoint && list_empty(&data->select.dispose))
		__d_drop(data->select.start);
		}

		@@ -1536,17 +1536,15 @@ void d_invalidate(struct dentry *dentry)

		d_walk(dentry, &data, detach_and_collect, check_and_drop);

		if (data.select.found)
		if (!list_empty(&data.select.dispose))
		shrink_dentry_list(&data.select.dispose);
		else if (!data.mountpoint)
		return;

		if (data.mountpoint) {
		detach_mounts(data.mountpoint);
		dput(data.mountpoint);
		}

		if (!data.mountpoint && !data.select.found)
		break;

		cond_resched();
		}
		}

Admin message