[PATCH] locks: fix possible infinite loop in posix deadlock detection

J. Bruce Fields
2007-10-28T17:32:18Z

From: J. Bruce Fields <bfields@citi.umich.edu>

I think the real solution is to remove deadlock detection completely;
it's hard to imaagine applications really depend on it anyway.

For now, though, just bail out after a few iterations.

Thanks to George Davis for reporting the problem.

Cc: "George G. Davis" <gdavis@mvista.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
---
fs/locks.c | 12 ++++++++++++
1 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/fs/locks.c b/fs/locks.c
index 0127a28..131aa88 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -696,17 +696,29 @@ EXPORT_SYMBOL(posix_test_lock);
* Note: the above assumption may not be true when handling lock requests
* from a broken NFS client. But broken NFS clients have a lot more to
* worry about than proper deadlock detection anyway... --okir
+ *
+ * However, the failure of this assumption (also possible in the case of
+ * multiple tasks sharing the same open file table) also means there's no
+ * guarantee that the loop below will terminate. As a hack, we give up
+ * after a few iterations. We don't bother returning EDEADLK in that case;
+ * the deadlock has probably already happened anyway.
*/
+
+#define MAX_DEADLK_ITERATIONS 10
+
static int posix_locks_deadlock(struct file_lock *caller_fl,
struct file_lock *block_fl)
{
struct file_lock *fl;
+ int i = 0;

next_task:
if (posix_same_owner(caller_fl, block_fl))
return 1;
list_for_each_entry(fl, &blocked_list, fl_link) {
if (posix_same_owner(fl, block_fl)) {
+ if (i++ > MAX_DEADLK_ITERATIONS)
+ return 0;
fl = fl->fl_next;
block_fl = fl;
goto next_task;
--
1.5.3.4.208.gc990