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Commit 57b65325 authored by Jeff Layton's avatar Jeff Layton
Browse files

locks: skip deadlock detection on FL_FILE_PVT locks 



It's not really feasible to do deadlock detection with FL_FILE_PVT
locks since they aren't owned by a single task, per-se. Deadlock
detection also tends to be rather expensive so just skip it for
these sorts of locks.

Also, add a FIXME comment about adding more limited deadlock detection
that just applies to ro -> rw upgrades, per Andy's request.

Cc: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: default avatarJeff Layton <jlayton@redhat.com>
parent c1e62b8f

fs/locks.c

+17 −2
Original line number Diff line number Diff line
@@ -564,7 +564,7 @@ static void __locks_insert_block(struct file_lock *blocker, 
	BUG_ON(!list_empty(&waiter->fl_block));

	waiter->fl_next = blocker;

	list_add_tail(&waiter->fl_block, &blocker->fl_block);

	if (IS_POSIX(blocker))

	if (IS_POSIX(blocker) && !IS_FILE_PVT(blocker))

		locks_insert_global_blocked(waiter);

}
@@ -757,8 +757,16 @@ EXPORT_SYMBOL(posix_test_lock); 
 * Note: the above assumption may not be true when handling lock

 * requests from a broken NFS client. It may also fail in the presence

 * of tasks (such as posix threads) sharing the same open file table.

 *

 * To handle those cases, we just bail out after a few iterations.

 *

 * For FL_FILE_PVT locks, the owner is the filp, not the files_struct.

 * Because the owner is not even nominally tied to a thread of

 * execution, the deadlock detection below can't reasonably work well. Just

 * skip it for those.

 *

 * In principle, we could do a more limited deadlock detection on FL_FILE_PVT

 * locks that just checks for the case where two tasks are attempting to

 * upgrade from read to write locks on the same inode.

 */



#define MAX_DEADLK_ITERATIONS 10
@@ -781,6 +789,13 @@ static int posix_locks_deadlock(struct file_lock *caller_fl, 
{

	int i = 0;



	/*

	 * This deadlock detector can't reasonably detect deadlocks with

	 * FL_FILE_PVT locks, since they aren't owned by a process, per-se.

	 */

	if (IS_FILE_PVT(caller_fl))

		return 0;



	while ((block_fl = what_owner_is_waiting_for(block_fl))) {

		if (i++ > MAX_DEADLK_ITERATIONS)

			return 0;