[PATCH] fs/locks.c: Fix posix locking for threaded tasks

[Matthew Wilcox <willy@debian.org>]

Saurabh Desai believes that locks created by threads should not conflict
with each other.  I'm inclined to agree; I don't know why the test for
->fl_pid was added, but the comment suggests that whoever added it wasn't
sure either.

Frankly, I have no clue about the intended semantics for threads, and
SUS v3 does not offer any enlightenment.  But it seems reasonable that
processes which share a files_struct should share locks.  After all,
if one process closes the fd, they'll remove locks belonging to the
other process.

Here's a patch generated against 2.4; it also applies to 2.5.
Please apply.

===== fs/locks.c 1.9 vs edited =====
--- 1.9/fs/locks.c	Mon Jun  3 18:49:43 2002
+++ edited/fs/locks.c	Fri Jun  7 21:24:12 2002
@@ -380,15 +380,12 @@
 }
 
 /*
- * Check whether two locks have the same owner
- * N.B. Do we need the test on PID as well as owner?
- * (Clone tasks should be considered as one "owner".)
+ * Locks are deemed to have the same owner if the tasks share files_struct.
  */
 static inline int
 locks_same_owner(struct file_lock *fl1, struct file_lock *fl2)
 {
-	return (fl1->fl_owner == fl2->fl_owner) &&
-	       (fl1->fl_pid   == fl2->fl_pid);
+	return (fl1->fl_owner == fl2->fl_owner);
 }
 
 /* Remove waiter from blocker's block list.

-- 
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