linux-kernel - [PATCH v2] CAPI: Silence lockdep warning on get_capi_appl_by

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Message-ID: <4CBB13B7.8080705@web.de>
Date:	Sun, 17 Oct 2010 17:18:15 +0200
From:	Jan Kiszka <jan.kiszka@....de>
To:	"David S. Miller" <davem@...emloft.net>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	i4ldeveloper@...tserv.isdn4linux.de,
	Linux Netdev List <netdev@...r.kernel.org>,
	Karsten Keil <isdn@...ux-pingi.de>,
	Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH v2] CAPI: Silence lockdep warning on get_capi_appl_by_nr usage

As long as we hold capi_controller_lock, we can safely access
capi_applications without RCU protection as no one can modify the
application list underneath us. Introduce an RCU-free
__get_capi_appl_by_nr for this purpose. This silences lockdep warnings
on suspicious rcu_dereference usage.

Signed-off-by: Jan Kiszka <jan.kiszka@....de>
---

v2:
 - use lockdep_assert_held in favor of WARN_ON_ONCE(!mutex_is_locked)
   as suggested by Peter

 drivers/isdn/capi/kcapi.c |   19 ++++++++++++++-----
 1 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/drivers/isdn/capi/kcapi.c b/drivers/isdn/capi/kcapi.c
index 2648d39..2b33b26 100644
--- a/drivers/isdn/capi/kcapi.c
+++ b/drivers/isdn/capi/kcapi.c
@@ -99,6 +99,16 @@ static inline struct capi_ctr *get_capi_ctr_by_nr(u16 contr)
 	return capi_controller[contr - 1];
 }
 
+static inline struct capi20_appl *__get_capi_appl_by_nr(u16 applid)
+{
+	lockdep_assert_held(&capi_controller_lock);
+
+	if (applid - 1 >= CAPI_MAXAPPL)
+		return NULL;
+
+	return capi_applications[applid - 1];
+}
+
 static inline struct capi20_appl *get_capi_appl_by_nr(u16 applid)
 {
 	if (applid - 1 >= CAPI_MAXAPPL)
@@ -186,10 +196,9 @@ static void notify_up(u32 contr)
 		ctr->state = CAPI_CTR_RUNNING;
 
 		for (applid = 1; applid <= CAPI_MAXAPPL; applid++) {
-			ap = get_capi_appl_by_nr(applid);
-			if (!ap)
-				continue;
-			register_appl(ctr, applid, &ap->rparam);
+			ap = __get_capi_appl_by_nr(applid);
+			if (ap)
+				register_appl(ctr, applid, &ap->rparam);
 		}
 
 		wake_up_interruptible_all(&ctr->state_wait_queue);
@@ -216,7 +225,7 @@ static void ctr_down(struct capi_ctr *ctr, int new_state)
 	memset(ctr->serial, 0, sizeof(ctr->serial));
 
 	for (applid = 1; applid <= CAPI_MAXAPPL; applid++) {
-		ap = get_capi_appl_by_nr(applid);
+		ap = __get_capi_appl_by_nr(applid);
 		if (ap)
 			capi_ctr_put(ctr);
 	}
-- 
1.7.1
--
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