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From:   Qian Cai <cai@lca.pw>
To:     peterz@infradead.org
Cc:     mark.rutland@arm.com, akpm@linux-foundation.org,
        linux-kernel@vger.kernel.org, Qian Cai <cai@lca.pw>
Subject: [PATCH -next] fork: silence a false postive warning in __mmdrop
Date:   Thu,  4 Jun 2020 11:03:44 -0400
Message-Id: <20200604150344.1796-1-cai@lca.pw>
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Sender: linux-kernel-owner@vger.kernel.org
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The linux-next commit bf2c59fce407 ("sched/core: Fix illegal RCU from
offline CPUs") delayed,

idle->active_mm = &init_mm;

into finish_cpu() instead of idle_task_exit() which results in a false
positive warning that was originally designed in the commit 3eda69c92d47
("kernel/fork.c: detect early free of a live mm").

 WARNING: CPU: 127 PID: 72976 at kernel/fork.c:697
 __mmdrop+0x230/0x2c0
 do_exit+0x424/0xfa0
 Call Trace:
 do_exit+0x424/0xfa0
 do_group_exit+0x64/0xd0
 sys_exit_group+0x24/0x30
 system_call_exception+0x108/0x1d0
 system_call_common+0xf0/0x278

Fixes: bf2c59fce407 ("sched/core: Fix illegal RCU from offline CPUs")
Signed-off-by: Qian Cai <cai@lca.pw>
---
 kernel/fork.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index 142b23645d82..5334efd2a680 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -694,7 +694,6 @@ void __mmdrop(struct mm_struct *mm)
 {
 	BUG_ON(mm == &init_mm);
 	WARN_ON_ONCE(mm == current->mm);
-	WARN_ON_ONCE(mm == current->active_mm);
 	mm_free_pgd(mm);
 	destroy_context(mm);
 	mmu_notifier_subscriptions_destroy(mm);
-- 
2.21.0 (Apple Git-122.2)