linux-ext4 - [PATCH v15 30/43] cpu/hotplug: use a weaker annotation in AP thread

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Message-Id: <20250513100730.12664-31-byungchul@sk.com>
Date: Tue, 13 May 2025 19:07:17 +0900
From: Byungchul Park <byungchul@...com>
To: linux-kernel@...r.kernel.org
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Subject: [PATCH v15 30/43] 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.

Replace 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 b08bb34b1718..3eecd0a7b5b3 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -537,7 +537,7 @@ 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