+ kfence-test-try-to-avoid-test_gfpzero-trigger-rcu_stall.patch added to -mm tree

+ kfence-test-try-to-avoid-test_gfpzero-trigger-rcu_stall.patch added to -mm tree

[Andrew Morton]

The patch titled
     Subject: kfence: test: try to avoid test_gfpzero trigger rcu_stall
has been added to the -mm tree.  Its filename is
     kfence-test-try-to-avoid-test_gfpzero-trigger-rcu_stall.patch

This patch should soon appear at
    https://ozlabs.org/~akpm/mmots/broken-out/kfence-test-try-to-avoid-test_gfpzero-trigger-rcu_stall.patch
and later at
    https://ozlabs.org/~akpm/mmotm/broken-out/kfence-test-try-to-avoid-test_gfpzero-trigger-rcu_stall.patch

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------------------------------------------------------
From: Peng Liu <liupeng256@huawei.com>
Subject: kfence: test: try to avoid test_gfpzero trigger rcu_stall

When CONFIG_KFENCE_NUM_OBJECTS is set to a big number, kfence
kunit-test-case test_gfpzero will eat up nearly all the CPU's resources
and rcu_stall is reported as the following log which is cut from a
physical server.

  rcu: INFO: rcu_sched self-detected stall on CPU
  rcu: 	68-....: (14422 ticks this GP) idle=6ce/1/0x4000000000000002
  softirq=592/592 fqs=7500 (t=15004 jiffies g=10677 q=20019)
  Task dump for CPU 68:
  task:kunit_try_catch state:R  running task
  stack:    0 pid: 9728 ppid:     2 flags:0x0000020a
  Call trace:
   dump_backtrace+0x0/0x1e4
   show_stack+0x20/0x2c
   sched_show_task+0x148/0x170
   ...
   rcu_sched_clock_irq+0x70/0x180
   update_process_times+0x68/0xb0
   tick_sched_handle+0x38/0x74
   ...
   gic_handle_irq+0x78/0x2c0
   el1_irq+0xb8/0x140
   kfree+0xd8/0x53c
   test_alloc+0x264/0x310 [kfence_test]
   test_gfpzero+0xf4/0x840 [kfence_test]
   kunit_try_run_case+0x48/0x20c
   kunit_generic_run_threadfn_adapter+0x28/0x34
   kthread+0x108/0x13c
   ret_from_fork+0x10/0x18

To avoid rcu_stall and unacceptable latency, a schedule point is
added to test_gfpzero.

Link: https://lkml.kernel.org/r/20220309083753.1561921-4-liupeng256@huawei.com
Signed-off-by: Peng Liu <liupeng256@huawei.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Brendan Higgins <brendanhiggins@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Wang Kefeng <wangkefeng.wang@huawei.com>
Cc: Daniel Latypov <dlatypov@google.com>
Cc: David Gow <davidgow@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/kfence/kfence_test.c |    1 +
 1 file changed, 1 insertion(+)

--- a/mm/kfence/kfence_test.c~kfence-test-try-to-avoid-test_gfpzero-trigger-rcu_stall
+++ a/mm/kfence/kfence_test.c
@@ -627,6 +627,7 @@ static void test_gfpzero(struct kunit *t
 			kunit_warn(test, "giving up ... cannot get same object back\n");
 			return;
 		}
+		cond_resched();
 	}
 
 	for (i = 0; i < size; i++)
_

Patches currently in -mm which might be from liupeng256@huawei.com are

kunit-fix-uaf-when-run-kfence-test-case-test_gfpzero.patch
kunit-make-kunit_test_timeout-compatible-with-comment.patch
kfence-test-try-to-avoid-test_gfpzero-trigger-rcu_stall.patch