linux-kernel - [PATCH v12 14/27] cpu/hotplug: Use a weaker annotation in AP thread

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Message-Id: <20240221094933.36348-15-byungchul@sk.com>
Date: Wed, 21 Feb 2024 18:49:20 +0900
From: Byungchul Park <byungchul@...com>
To: linux-kernel@...r.kernel.org
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Subject: [PATCH v12 14/27] cpu/hotplug: Use a weaker annotation in AP thread

cb92173d1f0 ("locking/lockdep, cpu/hotplug: Annotate AP thread") was
introduced to make lockdep_assert_cpus_held() work in AP thread.

However, the annotation is too strong for that purpose. We don't have to
use more than try lock annotation for that.

rwsem_acquire() implies:

   1. might be a waiter on contention of the lock.
   2. enter to the critical section of the lock.

All we need in here is to act 2, not 1. So trylock version of annotation
is sufficient for that purpose. Now that dept partially relies on
lockdep annotaions, dept interpets rwsem_acquire() as a potential wait
and might report a deadlock by the wait. So replaced it with trylock
version of annotation.

Signed-off-by: Byungchul Park <byungchul@...com>
---
 kernel/cpu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index a86972a91991..b708989f789f 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -535,7 +535,7 @@ int lockdep_is_cpus_held(void)
 
 static void lockdep_acquire_cpus_lock(void)
 {
-	rwsem_acquire(&cpu_hotplug_lock.dep_map, 0, 0, _THIS_IP_);
+	rwsem_acquire(&cpu_hotplug_lock.dep_map, 0, 1, _THIS_IP_);
 }
 
 static void lockdep_release_cpus_lock(void)
-- 
2.17.1