From: John Stultz <jstultz@google.com>
Date: Fri, 22 Sep 2023 04:36:01 +0000 (+0000)
Subject: locking/ww_mutex/test: Make sure we bail out instead of livelock
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=cfa92b6d52071aaa8f27d21affdcb14e7448fbc1;p=linux.git

locking/ww_mutex/test: Make sure we bail out instead of livelock

I've seen what appears to be livelocks in the stress_inorder_work()
function, and looking at the code it is clear we can have a case
where we continually retry acquiring the locks and never check to
see if we have passed the specified timeout.

This patch reworks that function so we always check the timeout
before iterating through the loop again.

I believe others may have hit this previously here:

  https://lore.kernel.org/lkml/895ef450-4fb3-5d29-a6ad-790657106a5a@intel.com/

Reported-by: Li Zhijian <zhijianx.li@intel.com>
Signed-off-by: John Stultz <jstultz@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20230922043616.19282-4-jstultz@google.com
---

diff --git a/kernel/locking/test-ww_mutex.c b/kernel/locking/test-ww_mutex.c
index 358d661504269..78719e1ef1b11 100644
--- a/kernel/locking/test-ww_mutex.c
+++ b/kernel/locking/test-ww_mutex.c
@@ -465,17 +465,18 @@ retry:
 			ww_mutex_unlock(&locks[order[n]]);
 
 		if (err == -EDEADLK) {
-			ww_mutex_lock_slow(&locks[order[contended]], &ctx);
-			goto retry;
+			if (!time_after(jiffies, stress->timeout)) {
+				ww_mutex_lock_slow(&locks[order[contended]], &ctx);
+				goto retry;
+			}
 		}
 
+		ww_acquire_fini(&ctx);
 		if (err) {
 			pr_err_once("stress (%s) failed with %d\n",
 				    __func__, err);
 			break;
 		}
-
-		ww_acquire_fini(&ctx);
 	} while (!time_after(jiffies, stress->timeout));
 
 	kfree(order);