Messages in this thread Patch in this message | | | Date | Thu, 15 Dec 2005 04:09:13 +0530 | From | Dinakar Guniguntala <> | Subject | Recursion bug in -rt |
| |
Hi David,
I hit this bug with -rt22-rf11
========================================== [ BUG: lock recursion deadlock detected! | ------------------------------------------ already locked: [f7abbc94] {futex} .. held by: testpi-3: 4595 [f7becdd0, 59] ... acquired at: futex_wait_robust+0x142/0x1f3 ------------------------------ | showing all locks held by: | (testpi-3/4595 [f7becdd0, 59]): ------------------------------
#001: [f7abbc94] {futex} ... acquired at: futex_wait_robust+0x142/0x1f3
-{current task's backtrace}-----------------> [<c0103e04>] dump_stack+0x1e/0x20 (20) [<c0136bc2>] check_deadlock+0x2d7/0x334 (44) [<c01379bc>] task_blocks_on_lock+0x2c/0x224 (36) [<c03f29c5>] __down_interruptible+0x37c/0x95d (160) [<c013aebf>] down_futex+0xa3/0xe7 (40) [<c013ebc5>] futex_wait_robust+0x142/0x1f3 (72) [<c013f35c>] do_futex+0x9a/0x109 (40) [<c013f4dd>] sys_futex+0x112/0x11e (68) [<c0102f03>] sysenter_past_esp+0x54/0x75 (-8116) ------------------------------ | showing all locks held by: | (testpi-3/4595 [f7becdd0, 59]): ------------------------------
#001: [f7abbc94] {futex} ... acquired at: futex_wait_robust+0x142/0x1f3
---------------------------------------------------------------------
futex.c -> futex_wait_robust
if ((curval & FUTEX_PID) == current->pid) { ret = -EAGAIN; goto out_unlock; }
rt.c -> down_futex
if (!owner_task || owner_task == current) { up(sem); up_read(¤t->mm->mmap_sem); return -EAGAIN; }
I noticed that both the above checks below have been removed in your patch. I do understand that the futex_wait_robust path has been made similar to the futex_wait path, but I think we are not taking PI into consideration. Basically it looks like we still need to check if the current task has become owner. or are we missing a lock somewhere ?
I added the down_futex check above and my test has been running for hours without the oops. Without this check it used to oops within minutes.
Patch that works for me attached below. Thoughts?
-Dinakar
Index: linux-2.6.14-rt22-rayrt5/kernel/rt.c =================================================================== --- linux-2.6.14-rt22-rayrt5.orig/kernel/rt.c 2005-12-15 02:15:13.000000000 +0530 +++ linux-2.6.14-rt22-rayrt5/kernel/rt.c 2005-12-15 02:18:29.000000000 +0530 @@ -3001,7 +3001,7 @@ * if the owner can't be found return try again. */ - if (!owner_task) { + if (!owner_task || owner_task == current) { up(sem); up_read(¤t->mm->mmap_sem); return -EAGAIN; | |